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Old 02-10-2010, 02:29 PM   #1
Essex_29
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Default Proportioning valve delete

I have a GM brake system From a 1975 Olds Cutlass (Main cylinder, front disc brakes and proportioning valve). The rear axle is a 9" Ford and the drum brakes are very inefficient, though everything's new. The rear brakes work, but seem to need more pressure than the GM drum brakes did. I'd like to get the innards out of the prop valve and reconnect the lines.

When I open the screw on plug on the rear of the prop valve, where the rear line goes in the center, there's just a round thingy inside with a small hole in it...

Does anybody know how to disassemble this thing?
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Old 02-10-2010, 03:39 PM   #2
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Default Re: Proportioning valve delete

The smart thing to do is remove the 35 year old GM valve and install a NEW adjustable prop valve. I hope the rest of the system is new or rebuilt, and not also 35 years old.
Bob
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Old 02-10-2010, 05:31 PM   #3
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Default Re: Proportioning valve delete

V8 Bob beat me to the punch! An adjustable proportioning valve is better than none at all.
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Old 02-10-2010, 06:03 PM   #4
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Default Re: Proportioning valve delete

X3 - New adjustable valve
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Old 02-10-2010, 06:05 PM   #5
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Default Re: Proportioning valve delete

x4 here.
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Old 02-10-2010, 06:46 PM   #6
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Default Re: Proportioning valve delete

May I dissent?
At the moment, you don't even know if you need a proportioning valve. Take it out and try a couple of panic stops, preferably while someone is watching. I did that, the Wife said the rears did not lock up. The very slightly used proportioning valve is resting comfortably in a drawer.

That was in an extreme lash up - Pontiac Grand Prix front rotors, squeezed by GM "metric' calipers and Saturn disc's in the rear, all in a Sunbeam Alpine. Who woulda thought it would be about perfect?

But to answer your question, don't have a clue about taking the proportioning valve apart.
Bill
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Old 02-10-2010, 06:59 PM   #7
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Default Re: Proportioning valve delete

i cant imagine there would be that much difference in the wheel cylinders of the ford and gm.i would at least make sure they are working right and the shoes are mounted correctly.as in the front shoe is mounted in the front location...and adjusted......
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Old 02-10-2010, 07:06 PM   #8
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Default Re: Proportioning valve delete

I agree with B Blue..............a proportioning valve is not always necessary......in fact, probably seldom necessary on most rods. There are numerous variables when rod systems are put together and the only way to know if you need a prop valve is to leave it out and test the brake performance. The goal is, if any brakes lock in a "panic" stop, it should be the front brakes not the rears. Be sure when testing you have tire pressures set to normal levels.

Ray
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Old 02-10-2010, 08:02 PM   #9
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Default Re: Proportioning valve delete

I have had similar probs and its never the proportioning valve. And there is a reason cars have them. First off are you using silicone brake fluid it entraps air and is a pain to bleed. Bleed the brakes really well make sure the shoes are adjusted up. Try the basics first before you shit can the prop. valve.

Pat
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Old 02-10-2010, 08:20 PM   #10
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Default Re: Proportioning valve delete

What you have is a combination valve. Th proportioning valve is part of it. Are you sure you have the valve plumbed right? I think the part you are looking at inside works like a residual valve. A friend hooked his up wrong and was having the same problem. The residual valve would not allow enough fluid to pass to the rear to operate the drum brakes. He removed the residual and viola! rear brakes.
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Old 02-10-2010, 08:32 PM   #11
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Default Re: Proportioning valve delete

The combo valve is designed to trip and limit brake pressure to the rear (or the front) if you get a line torn open. If there's not enough pressure in that side of the system, it trips - for instance if there's air in the lines. That way you can actually stop and maybe even nurse your car to a garage, if you have a problem, without killing yourself or others.

So how about just bleeding the brakes and see how it is then? And make sure it's plumbed right, too. I just did a rear line and wheel cylinder in a late model van and all I had to do was let the fluid run gravity bleeding it for a while and it stops fine.

Disc front, drum rear needs a prop valve. Only all drum or all disc systems don't require one.
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Old 02-10-2010, 09:14 PM   #12
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Default Re: Proportioning valve delete

Quote:
Originally Posted by rustynewyorker View Post

Disc front, drum rear needs a prop valve. Only all drum or all disc systems don't require one.
Simply not the case. I know, I know, all the "factory" systems use them with disc/drum. But, as I alluded to in post above, when a hobbyist puts together a hot rod usually it is a combination of parts from several sources, not a complete and engineered system, not to mention the varying weight distribution, big & little tires, mismatched calipers to master cylinder bore and so on.

This is not just my theory.......but my experience in practice. My last build was a '47 Ford Coupe, flathead, 3 speed '50 Merc trans, 8" ford rear axle. stock I beam front axle with Speedway disc kit. The rotors were 12" F-100/150 and full size '71/'76 GM calipers. Rear brakes were 10"x 1 3/4 stock Ford drums. Stock brake pedal with master cylinder from a '67/'72 Mustang. NO brake booster. Had residual valves, 2# frt/ 10# rear. No proportioning valve. 205/70-15 frt, 235/70-15 rear tires

With the large rotors and big calipers I had excellent brakes with very moderate pedal pressure with no lock up on rear when making maximum braking effort. A different combination of rotor and/or caliper size, M/C bore, tire size, brake lining friction coefficient and so on may produce different results.

Ray
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Old 02-10-2010, 09:25 PM   #13
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Default Re: Proportioning valve delete

Quote:
Originally Posted by Hnstray View Post
Simply not the case. I know, I know, all the "factory" systems use them with disc/drum. But, as I alluded to in post above, when a hobbyist puts together a hot rod usually it is a combination of parts from several sources, not a complete and engineered system, not to mention the varying weight distribution, big & little tires, mismatched calipers to master cylinder bore and so on.

This is not just my theory.......but my experience in practice. My last build was a '47 Ford Coupe, flathead, 3 speed '50 Merc trans, 8" ford rear axle. stock I beam front axle with Speedway disc kit. The rotors were 12" F-100/150 and full size '71/'76 GM calipers. Rear brakes were 10"x 1 3/4 stock Ford drums. Stock brake pedal with master cylinder from a '67/'72 Mustang. NO brake booster. Had residual valves, 2# frt/ 10# rear. No proportioning valve. 205/70-15 frt, 235/70-15 rear tires

With the large rotors and big calipers I had excellent brakes with very moderate pedal pressure with no lock up on rear when making maximum braking effort. A different combination of rotor and/or caliper size, M/C bore, tire size, brake lining friction coefficient and so on may produce different results.

Ray
x 2

I have a very similar set up on my '40 pickup, and no prop valve. Seems to work just fine.
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Old 02-10-2010, 10:14 PM   #14
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Default Re: Proportioning valve delete

So after reading these posts - one would be led to believe that IF the rears don't lock up in a panic stop then you are fine - no proportioning valve needed!!!!

But, I'm afraid it's more complicated than that - otherwise the "factory" would have simply found the smallest least effective rear brake set up possible and eliminated the proportioning valve and it's associated cost as well.

The factory was trying to optimize the braking under various conditions - I even recall some pickups having a variable proportioning valve based on the load in the truck bed!

YMMV
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Old 02-10-2010, 11:10 PM   #15
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Default Re: Proportioning valve delete

So many people are quick to jump on the "you need an adjustable proportioning valve" bandwagon...if your rear brakes are innefficient now, why would you want to decrease the line pressure to them?
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Old 02-11-2010, 07:10 AM   #16
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Default Re: Proportioning valve delete

When I switched to front discs on my 55 DeSoto with Kelsey-Hayes power brakes, I did NOTHING to anything else on the brake system...no proportioning valve, residual valve, daul master cylinder, etc. There was NO change in the pedal travel and pressure was the same. The car now stops straight, and if necessary I can lock up all 4 wheels...and I use Silicone brake fluid...
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Old 02-11-2010, 07:26 AM   #17
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Smile Re: Proportioning valve delete

Quote:
Originally Posted by HemiRambler View Post
So after reading these posts - one would be led to believe that IF the rears don't lock up in a panic stop then you are fine - no proportioning valve needed!!!!

But, I'm afraid it's more complicated than that - otherwise the "factory" would have simply found the smallest least effective rear brake set up possible and eliminated the proportioning valve and it's associated cost as well.

The factory was trying to optimize the braking under various conditions - I even recall some pickups having a variable proportioning valve based on the load in the truck bed!

YMMV

You are correct "it is more complicated than that".............which is precisely the point I tried to make. So we agree!

The thing is, unless one fully understands all the factors and variables and the engineering principles involved, anything we cobble together is probably not going to be optimum. May be close, may be far from it it. That said, it is ridiculous to say "anytime you install a disc/drum system you MUST HAVE a proportioning valve". Sometimes you need one...sometimes you don't.

The pickups you talk about with the pro valve were certainly warranted.
A pickup, when unloaded, is obviously much lighter weight on the rear wheels, and more prone to lock up, than when loaded and greater weight increases tire traction.......reducing the tendency to lock up. Most of our cars do not get the wide range of weight distribution change that a pickup encounters.

Ray
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Old 02-11-2010, 07:43 AM   #18
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Default Re: Proportioning valve delete

how good are you at steering doing 65 with no brakes
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Old 02-11-2010, 07:48 AM   #19
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Default Re: Proportioning valve delete

Since we're talking proportioning valve.......... Sorry to be so dumb, but i gotta know!

Mine has the knob on the side and it has an arrow that says " LESS BRAKE" in the direction of the arrow, WHAT DOES IT MEAN? Less brake in the front or rear? what's the best adjustment. I have rear drums and front discs. My brakes are fine right now, but i want them to be the best they can!! Thanx!!
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Old 02-11-2010, 08:22 AM   #20
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Default Re: Proportioning valve delete

I have to agree with Hnstray, it seems like proportioning valves are used as a cure all for all brake problems, and they rarely do anything at all. I DO NOT install them on any of the brake systems I build whether they be disc/drum or disc/disc, because they limit the rear brakes so little that they are ineffective. There is more to be gained altering M/C bore diameters, wheel cylinder diameters and pedal ratios than any valve could offer.
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Old 02-11-2010, 08:50 AM   #21
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Default Re: Proportioning valve delete

Quote:
Originally Posted by chop32 View Post
So many people are quick to jump on the "you need an adjustable proportioning valve" bandwagon...if your rear brakes are innefficient now, why would you want to decrease the line pressure to them?
You may want to consider that the combo valve he's using is reducing the pressure to the rear too much. An adjustable would allow the bias on the the rear brakes to be increased over what the combo valve is doing.
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Old 02-11-2010, 09:07 AM   #22
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Default Re: Proportioning valve delete

I had to add a prop valve in my 68 F100 that the P.O had converted to discs from a 72. It had a 351W and T-5 and I picked it up cheap because of brake problems. Just the weight of the pedal would lock up the rear brakes. I added a junkyard prop valve, and suddenly everything worked great, so I would think they do some good.
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Old 02-11-2010, 09:23 AM   #23
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Default Re: Proportioning valve delete

Quote:
Originally Posted by B Blue View Post
May I dissent?
At the moment, you don't even know if you need a proportioning valve. Take it out and try a couple of panic stops, preferably while someone is watching. I did that, the Wife said the rears did not lock up. The very slightly used proportioning valve is resting comfortably in a drawer.
Bill
For one, I agree. If you don't have problems with the rears locking prematurely, you don't need a proportioning valve. BTW, they're gonna lock because of weight bias in a panic stop, but they can't lock at the slightest touch of the pedal.
Two, and maybe more important, you say you may not be getting enough out of the rears? A proportioning valve isn't gonna ADD pressure to the rears.
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Old 02-11-2010, 12:10 PM   #24
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Default Re: Proportioning valve delete

Quote:
Originally Posted by Groucho View Post
...Two, and maybe more important, you say you may not be getting enough out of the rears? A proportioning valve isn't gonna ADD pressure to the rears.
Thats what I was trying to get accross about the adjustable proportioning valve...Ive had people say that it says more/less so it must increase your pressure...WRONG!
Its function is to lessen the pressure you have available.

Quote:
Originally Posted by Ian Berky View Post
Since we're talking proportioning valve.......... Sorry to be so dumb, but i gotta know!

Mine has the knob on the side and it has an arrow that says " LESS BRAKE" in the direction of the arrow, WHAT DOES IT MEAN? Less brake in the front or rear? what's the best adjustment. I have rear drums and front discs. My brakes are fine right now, but i want them to be the best they can!! Thanx!!
Sounds like you havent installed the valve yet? The valve should be installed in the rear brake line before the "T". If your rears dont lock up now you dont need it!
If your rears lock up easily, install the valve and turn it to the highest setting...do some panic stops as said earlier...adjust it down (less brake) until your rears dont lock up easily. As Groucho said, they will lock up a bit earlier due the the sudden shift in weight bias...the trick is to not limit them so much that they are innefective! Trial and error!
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Old 02-11-2010, 12:38 PM   #25
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Default Re: Proportioning valve delete

The goal is, if any brakes lock in a "panic" stop, it should be the front brakes not the rears

Nooooooooooooo!
That's only a test to see how well proportioned the systems are.
Locked front brakes: stops badly, and arrive sideways or backwards.
The moment the front tires skid, they have less traction than the other axle, and try to follow them - see where this goes?
If you have to lose 1 brake line - keep the rears. Been there, done that.

The amount of front vs. rear is complicated, because too many factors contribute:
wheelbase (short = more weight transfers forward)
tire radius (tall needs more brake)
suspension squat under braking
center of gravity (high = more weight transfers forward)
drum or rotor diameter
drum shoe width or caliper pad area
diameter of drum wheel cylinder or caliper cylinder

The reason a valve is used is because the much higher hydraulic pressure needed to move a caliper has already locked the rear drum, but any of these can be fudged to change front/rear, including drum+drum and disc-disc. A proportioning valve is just another tool.
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Old 02-11-2010, 01:28 PM   #26
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Default Re: Proportioning valve delete

Yes, if the fronts lock up, it stops badly and arrives sideways, but hardly every backwards. That's what happens when the rears lock up. When the rears lock up, you can do two things: let off the brake and/or steer into the resulting skid. Nether strategy has a desirable outcome.

So yes, the idea is for the fronts to lock up before the rears.

Bill
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Old 02-11-2010, 02:56 PM   #27
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Default Re: Proportioning valve delete

Thanks guys for all the thoughts and suggestions!

Firstly I already have a prop (combination) valve, plumbed just as it was from factory, only with new lines. The brakes are bled and adjusted, and they use oldfashioned paint removing brake fluid. And everything is new, not 35 years old, save for the main brake cylinder and combination valve.

The front brakes work just fine.
The rears can't be made to lock up on a brake dyno without help from the e-brake.

As this is the case, I was thinking that I may (with a lot of luck) get good brakes with the prop valve deleted. And after testing, if I don't I'll install an adjustable one. I'm on a budget, and any way, buying parts just to fill drawers, or in this case, a prop valve that may be used adjusted fully open is not what I want or need.

As for why car manufacturers use prop valves, I think that it must be more cost efficient to use a couple standard rear brake sizes, and adjust them for different needs with a prop valve.
This by the way is the beauty of american car parts: You need new rear brake shoes for a '70 LeMans, and you can by brake shoes for an '84 Caprice Station wagon! Of course they need prop valves!

And the original question is still unanwered
"Does anybody know how to disassemble this thing?"

Oh, and I can't resist writing about the skidding tires:
The axle with the skidding tires will always want to come first. That's why we'll want the front's to lock up a bit before the rears. Locking up the rears first will result in wide slides or worse in a bad case.
Test it yourself with a toy car. Tape two wheels so thet they can't move and push the car over the floor. If the front wheels are stationary, the car will continue in a straight line. If the rears are locked up, the car will turn, and continue backwards.
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Old 02-11-2010, 03:14 PM   #28
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Default Re: Proportioning valve delete

Quote:
Originally Posted by panic View Post
The goal is, if any brakes lock in a "panic" stop, it should be the front brakes not the rears

Nooooooooooooo!
That's only a test to see how well proportioned the systems are.
Locked front brakes: stops badly, and arrive sideways or backwards.
The moment the front tires skid, they have less traction than the other axle, and try to follow them - see where this goes?
If you have to lose 1 brake line - keep the rears. Been there, done that.


.

I must respectfully totally disagree with your stated opinion. It is the REAR brake lock up that will spin you sideways and/or backward, not the fronts.

Locked fronts do interfere with steering too some degree.....but that is a MUCH more stable condition than locked rears, you just 'plow' straight ahead. Think about the "bootleg turn".........crank the front wheels in direction of choice, usually left, and stab the brakes HARD to lock the rears and bring the back end around...
still not persuaded ..............take you car/truck onto a relatively slick surface, wet ot icy, and jam on the parking brake....and hang on!

Ray
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Old 02-11-2010, 06:04 PM   #29
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Default Re: Proportioning valve delete

Studebaker Avanti came from the factory with front disc - rear drum, single M/Cyl and no proportioning valve. Go figure. I think residual valves are more important. If stopping is a problem, install a midland booster on the front brakes. Remember, the front brakes do 70% of the stopping.
Not going is an inconvience- Not stopping is a problem!
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Old 02-11-2010, 08:47 PM   #30
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Default Re: Proportioning valve delete

Quote:
Originally Posted by Hnstray View Post
I must respectfully totally disagree with your stated opinion. It is the REAR brake lock up that will spin you sideways and/or backward, not the fronts.

Locked fronts do interfere with steering too some degree.....but that is a MUCH more stable condition than locked rears, you just 'plow' straight ahead. Think about the "bootleg turn".........crank the front wheels in direction of choice, usually left, and stab the brakes HARD to lock the rears and bring the back end around...
still not persuaded ..............take you car/truck onto a relatively slick surface, wet ot icy, and jam on the parking brake....and hang on!

Ray
Ray, you are 100 percent correct. Not only were anti lock brakes put on newer cars to shorten the stopping distance, they also allow, and most importantly, let you be able to still maintain steering the car in which ever direction you point it without cutting cookies. On most stock disc/drum brake set ups the front brakes do 65-75% of the brakeing so you can control the direction of the vehicle even if lockup occurs.
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Old 02-11-2010, 09:35 PM   #31
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Default Re: Proportioning valve delete

Apologies - engaged mouth before putting brain in gear.
My memory was "which brake of ONLY ONE would you rather have".

Duh!
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Old 02-11-2010, 09:59 PM   #32
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Default Re: Proportioning valve delete

So let me understand this - proportioning valves are junk - often not needed because those "in the know" will match the components - meaning tire size, m/c bore size, wheel cylinder size etc etc. Smells fishy to me. Are you guys suggesting that the "factory" with all their resources DIDN'T do this and used a proportioning valve as some sort of catch all fix it - and therefore "we" can engineer a system better thus scrapping this useless item???? I know no one said that exactly but that is what is being implied. BTW I am NOT taking any design cues from the Avante - sorry no sale.

Guys I surely agree that component matching is a great idea - I further suggest that "Detroit" did the SAME THING and still determined that they needed a proportioning valve. Keep in mind they were trying to OPTIMIZE the brake system under varying conditions - calling your system "good enough" as a result of a seat of your pants test is fine, but suggesting it is "as good" or even "better" is like saying Horrible Fright tools are as good as any others - sorry - like most things - you get what you pay for. A well designed brake system is no different.

I'd LOVE to hear some real experts from Bendix chime in - until then call me jaded.
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Old 02-11-2010, 10:25 PM   #33
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Default Re: Proportioning valve delete

Dear Jaded,

I don't think anyone has suggested they can engineer better than the factory boys...but that any particular combination of parts may or may not produce favorable braking characteristics. The de riguer installation of a proportioning valve is overdone. At least until one has tried out the brakes they installed under normal operating parameters.

I'll go further, though, and question whether or not all these factory jobs actually have "proportioning valves" at all............they certainly all have combination valves, as they are most correctly known, I believe. Their primary function is to close off flow of brake fluid to either the front or rear brake system (in some vehicles it's diagonal) in the event of a leak that produces a pressure differential sufficient to displace the 'shuttle valve' inside the comb valve. the comb valve also contains an electrical switch that turns on the brake warning light should such a failure occur. As for Avantis not having a pro valve.....hmm Avantis came out in '62 or '63 as I recall and dual circuit brake systems weren't intro'd until '67 on most cars..........so the early Avantis probably didn't have a Combination Valve/pro valve....whatever they really are.

Maybe on something besides pickup trucks there are combination valves that also act as proportioning valves, but I'll bet fewer than we all seem to think is the case.

I agree, be great to hear from a genuine brake engineer............

Regards,
ray
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Old 02-11-2010, 10:34 PM   #34
THE SPEED ADDICT
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Default Re: Proportioning valve delete

[QUOTE=Essex_29;4898049]Thanks guys for all the thoughts and suggestions!

The front brakes work just fine.
The rears can't be made to lock up on a brake dyno without help from the e-brake.



By pulling on the e-brake, your taking up the space between the brake shoe and the drum. If that's the case, it sounds like you'll need to adjust the brake shoes out farther so there in contact with the drum before the brake pedal is applied. If brake shoes are set correctly, the drum should barely slide on the assembly and there should be some drag on the drum when it's rotated.

Two symtoms of this are; low brake pedal, and low or no brake pressure at the wheels.
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Old 02-11-2010, 10:50 PM   #35
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Default Re: Proportioning valve delete

Lot's of commercial vehicles and some cars have a variable ride height sensitive prop valve to get optimal rear braking, that should tell you something about bias.
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Old 02-11-2010, 11:33 PM   #36
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Default Re: Proportioning valve delete

Quote:
Originally Posted by Hnstray View Post
Dear Jaded,

I don't think anyone has suggested they can engineer better than the factory boys...but that any particular combination of parts may or may not produce favorable braking characteristics. The de riguer installation of a proportioning valve is overdone. At least until one has tried out the brakes they installed under normal operating parameters.

I'll go further, though, and question whether or not all these factory jobs actually have "proportioning valves" at all............they certainly all have combination valves, as they are most correctly known, I believe. Their primary function is to close off flow of brake fluid to either the front or rear brake system (in some vehicles it's diagonal) in the event of a leak that produces a pressure differential sufficient to displace the 'shuttle valve' inside the comb valve. the comb valve also contains an electrical switch that turns on the brake warning light should such a failure occur. As for Avantis not having a pro valve.....hmm Avantis came out in '62 or '63 as I recall and dual circuit brake systems weren't intro'd until '67 on most cars..........so the early Avantis probably didn't have a Combination Valve/pro valve....whatever they really are.

Maybe on something besides pickup trucks there are combination valves that also act as proportioning valves, but I'll bet fewer than we all seem to think is the case.

I agree, be great to hear from a genuine brake engineer............

Regards,
ray
I agree 100% with everything you have said. I have dis-assembled the brass combo valve/ prop valve or whatever it is called, and I cannot figure out where the proportioning comes from. I can see the pressure differential valve, as well as the brake warning light, but as far as I can tell there is no proportioning going on. Can someone prove me wrong with a cut away?
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Old 02-11-2010, 11:48 PM   #37
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Default Re: Proportioning valve delete

If the prop valve doesn't need to be reset, then you just need to adjust the shoes out further. Although if they work to slow you down well, I'm not sure there's a problem. GM even put rear anti-lock systems into some of it's light trucks in the late 80s-early 90s, I have one, and it seems like a useless waste to me - same truck without I could never get the rears to lock, but I could make the fronts lock any time on snow or mud.

Proportioning valves exist because disc brakes require more pressure to operate than drum. Perhaps Studebaker used some other trick to acheive the same effect on the Avanti. Carmakers added the combo valve to them so you'd have some kind of brakes in the event of a failure resulting in a heavy leak, beyond the couple extra pumps a dual-chamber master gets you. I wouldn't run without one.
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Old 02-12-2010, 12:38 AM   #38
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Default Re: Proportioning valve delete

Quote:
Originally Posted by rustynewyorker View Post
Proportioning valves exist because disc brakes require more pressure to operate than drum..
Fronts can stand more pressure regardless of the type of brake

Quote:
Originally Posted by rustynewyorker View Post
GM even put rear anti-lock systems into some of it's light trucks in the late 80s-early 90s, I have one, and it seems like a useless waste to me - same truck without I could never get the rears to lock, but I could make the fronts lock any time on snow or mud.
The more weight on the wheel the more pressure can be applied without locking so with a variable valve the gain is improved braking with a load.
If you think about the nose down ass up weight transfer and how the way you apply the brake effects it you should be able to see any vehicle can theoretically benefit from variable pressure.

as for the original question which seems to have been sorta answered as I understand it if everything is installed and adjusted properly and isn't being throttled by a valve the next step is to look at the wheel cylinder diameter, here's a good explanation from aussie PeterR in another forum...

Quote:
Smaller piston diameter = smaller piston area = smaller force

With same diameter drum and same lining material, change in braking due to different cylinder diameter is:-

(NEW DIAM)X(NEW DIAM)
(OLD DIAM)X(OLD DIAM)

this means
if you go from 15/16 to 1, the braking will go up to 1.14 which is 14% more
if you go from 15/16 to 7/8, the braking will go down to .87 which is 13% less

If you know the proportion you want to change by, the formula can be reversed

(New diam) = (old diam) x square root(proportion)

say you want to reduce braking to .75

(new diam) = (15/16) x square root (.75)
= .812
which is very close to 13/16
plenty of good info here... http://www.stoptech.com/tech_info/te...e_papers.shtml

Last edited by ehdubya; 02-12-2010 at 02:15 AM. Reason: mo'info
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Old 02-12-2010, 01:42 AM   #39
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Default Re: Proportioning valve delete

The dics have stright brake curve but the drums is have a brake curve thats is not proposonal to the hydralic pressure
The brake capacity will rise more then the pressure in the brake system on drums but the disc it is proposanal to the pressure
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Old 02-12-2010, 03:36 AM   #40
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Default Re: Proportioning valve delete

For years, American cars had brakes with considerable servo action built in. That was so the 90 pound cutie down the street could stop a 4,000 pound car. That's also why they did not stop worth a crap when going backwards. The brake design was not changed when power brakes became available, even though the need for servo was greatly reduced. When US car makers first went to disc front, drum rear, they retained the servo style brakes and needed prop valves. Studebaker did not. Same with the British cars. They never had servo action and their disc/drum brakes worked fine with no prop valve.

Prop valves are not crap. They allow manufacturers to fine tune the front/ rear brake balance with a very minor change in the valve instead of modifying brake hardware. But they are not magic and are not required in all braking systems.

Bill
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Old 02-12-2010, 04:22 AM   #41
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Default Re: Proportioning valve delete

Quote:
Originally Posted by panic View Post
The goal is, if any brakes lock in a "panic" stop, it should be the front brakes not the rears

Nooooooooooooo!
That's only a test to see how well proportioned the systems are.
Locked front brakes: stops badly, and arrive sideways or backwards.
The moment the front tires skid, they have less traction than the other axle, and try to follow them - see where this goes?
If you have to lose 1 brake line - keep the rears. Been there, done that.

The amount of front vs. rear is complicated, because too many factors contribute:
wheelbase (short = more weight transfers forward)
tire radius (tall needs more brake)
suspension squat under braking
center of gravity (high = more weight transfers forward)
drum or rotor diameter
drum shoe width or caliper pad area
diameter of drum wheel cylinder or caliper cylinder

The reason a valve is used is because the much higher hydraulic pressure needed to move a caliper has already locked the rear drum, but any of these can be fudged to change front/rear, including drum+drum and disc-disc. A proportioning valve is just another tool.

Not true if the rears lock you get a loss of stability and more then likely a loose rear spin.

It's easy to prove just look at all the training cars used by police departments and driving schools for teaching spin and skid control and they all use a second brake pedal to lock the rears and cause spins bar none.
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Old 02-12-2010, 05:24 AM   #42
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Default Re: Proportioning valve delete

Yes,the Brit cars had non servo rear brakes....Early disc brake MG's stop well with little rear lock up,no valves of any kind,single chamber master cylinder.From what I see,Bendix servo brakes used on almost all US cars from the 1950 or so are prone to lock up and can be difficult to control at the verge of lock up compared to lets say earlier GM Huck brakes.The only Bendix adavnatage is less pedal pressure as mention in a previous post.
Not only avoiding lock up in panic stops,but during "normal" hard stops like when on a rural hiway and the light goes red .I had cars that would lock up during stops like this.
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Old 02-12-2010, 02:19 PM   #43
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Default Re: Proportioning valve delete

Quote:
Prop valves are not crap. They allow manufacturers to fine tune the front/ rear brake balance with a very minor change in the valve instead of modifying brake hardware. But they are not magic and are not required in all braking systems.
B Blue hit the nail here, I beleive this is why prop valves were (are?) used.

The original question in this thread was:

Does anybody know how to disassemble my 1975 Olds proportioning/ combination valve?

And the rear brakes are adjusted. They work, but are weak. The pedal isn't soft or bottoming out. I think they need more pressure. I can get more brake power with the e-brake, than the brake pedal, which make me think the brakes need more pressure, hence the idea of deliging the proportioning function of the combo valve.
If this works, I can retain the one circuit failure warning light.
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Old 02-12-2010, 04:42 PM   #44
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Default Re: Proportioning valve delete

Sorry, you've both missed the point of using a proportioning valve. It is NOT about adjusting the balance between the front and rear brakes to match components. I will explain but first lets understand some of the dynamics of car braking.

For the purpose of the explanation let's look at 2 tires - identical front and rear. Vehicle weight bias a "perfect" 50/50 split. Brakes the same front and rear. The front and rear are balanced in both load and braking ability. Life is good! Until we get to the dreaded WEIGHT TRANSFER. As you brake more the weight "shifts" towards the front of the car. So now our 50/50 split is lets' say 75/25. So now that those identical front tires are carrying more load they are also capable of stopping better too! But as those fronts stop BETTER the rears loose weight and with it ability to stop and therefore will lock up prematurely and skid - not good. So we add in a proportioning valve. the valve reduces the pressure to the rear - but it DOES NOT do this at some static value - it is DYNAMIC - there is a relationship involved that trys to mimick the weight transfer so that all wheels are carrying the OPTIMAL ability to brake. So considering this the statement that since "my rears don't lock up under a panic stop I am fine" ah not quite!!! First problem - since they didn't lock up you have no idea whether or not you are even CLOSE to maximum capacity - so they could be disconnected for that matter and you'd call it "good" . Yeah that's a problem. Next - what about all those conditions INBETWEEN max braking and normal driving - the stuff when raod conditions change - like rain or snow or loose gravel - whatever. Yeah the proportioning valve is trying to maximize your bias front to back at ALL PRESSURE RANGES not just at panic stop levels.
I understand a tiny teeny bit of this - but one thing I know for certain - BENDIX understands it better than I do and they say you need one so until you can prove better results without it - I'm gonna stick with them!!!

I would venture a guess that most people who toss them don't really understand what they even do.

Carry on !!!

Signed Jaded

Quote:
Originally Posted by Essex_29 View Post
B Blue hit the nail here, I beleive this is why prop valves were (are?) used.

The original question in this thread was:

Does anybody know how to disassemble my 1975 Olds proportioning/ combination valve?

And the rear brakes are adjusted. They work, but are weak. The pedal isn't soft or bottoming out. I think they need more pressure. I can get more brake power with the e-brake, than the brake pedal, which make me think the brakes need more pressure, hence the idea of deliging the proportioning function of the combo valve.
If this works, I can retain the one circuit failure warning light.
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Old 02-12-2010, 06:11 PM   #45
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Default Re: Proportioning valve delete

Essex 29, this is a bit wild, but worth considering. Guys with Sunbeam Alpines have been complaining about the same thing, but usually on the front. The problem has been old brake hose. They deteriorate internally and form flap valves under pressure. Are your rear hose(s) in good shape?

HemiRambler, what have you been smoking?

Bill
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Old 02-12-2010, 10:00 PM   #46
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Default Re: Proportioning valve delete

Oh please enlighten me oh wise one! I am all ears.

And BTW - ALL drum brakes have servo action - nature of the beast. What you tried to describe was the difference between SINGLE servo and DUAL Servo - but I'm sure according to you I have that wrong as well so please feel free to explain it - I can't wait.

Quote:
Originally Posted by B Blue View Post

HemiRambler, what have you been smoking?

Bill
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Old 02-13-2010, 06:45 AM   #47
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Default Re: Proportioning valve delete

No, you seem to be the only one that understands brakes, especially proportioning valves. Instead of me educating you, YOU need to educate US as 29 Essex also appears to not understand. A couple of links explaining the dynamic action of non suspension-linked proportioning valves would be a tremendous help.

Bill
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Old 02-13-2010, 06:58 AM   #48
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Default Re: Proportioning valve delete

Sorry I don't have any links handy or a scanner but I will see if these pics may help.

Read the text carefully - notice it doesn't say a proportioning valves reduces pressure - instead it says it REDUCES the pressure RISE. There is a distinct difference.

One of the points I am trying to make - is that the factory CAN & did match components - and yet they still chose to use a proportioning valve. The reason being WEIGHT transfer. One reason why CG affects the proportioning valve.
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Old 02-13-2010, 07:35 AM   #49
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Default Re: Proportioning valve delete

My 37 Ford has 72 Chevy half ton tk. master cylinder no power sys. 72 Monte Carlo frt. disc and 72 Impala sta. wag. rear drums. I used the 72 Monte prop. valve. Also use silicone brake fluid. The brakes have a solid hi pedal and you don't need much pressure on the pedal to stop. Almost feels like power brakes. I installed this system in 1986 and to date have never had any leaks in system and still have over half of the lining thickness.
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Old 02-13-2010, 07:46 AM   #50
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Default Re: Proportioning valve delete

Hey Guys what about a system that is used on race cars. 2 separate M/C and

a adjustable pivot point at the brake clevis?



Ago
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Old 02-13-2010, 09:03 AM   #51
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Default Re: Proportioning valve delete

And another question:

What's a better choice for a hot rod (4 wheel disc in my case) - late model OEM proportioning valve or Wilwood style adjustable type that goes in the rear line?

The OEM valve can influence both front and rear pressure (or the balance thereof) while the Wilwood can only lower pressure to the rear. I like the adjustability that the Wilwood provides, but can it work as well for brake balance without any reference to the front line pressure?
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Old 02-13-2010, 10:29 AM   #52
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Default Re: Proportioning valve delete

This thread/discussion has grown so large, with so much bad or incorrect brake info that it would be hard to know where to begin to explain, correct or discuss each item. Maybe if we took one subject at a time, i.e. drum brakes, disc brakes, combo valves, prop valves, dual masters, etc, we all might learn some facts, and dispel myths, rumors, bad magazine articles (that’s my favorite!), etc. I know many/most of you have not had the opportunity to learn first hand about vehicle brake systems, and that is very understandable. But it's amazing what some believe to be fact, in this day and age, with all the correct info and shop manuals available, and the fact modern brake systems have been out there for over 40 years! The brake system should be understood much better, because it is a very (most?) important system on a vehicle. JMO.
Bob

PS-I am NOT an expert, or an engineer, just a lowly technition that spent 35 years performing hands-on vehicle brake and chassis testing. JFYI.

Last edited by V8 Bob; 02-13-2010 at 10:46 AM. Reason: Adding personal info
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Old 02-13-2010, 11:26 AM   #53
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Default Re: Proportioning valve delete

Balance bar systems are a bird of a different feather! They do not have the dynamic ability that a proportioning valve offer - they do however work very well. In the race cars set up for "normal" road conditions they can set 'em for optimal road conditions & forget 'em - but the guys who race in the rain will change the braking bias via the adjustability feature to again maximize the braking for THOSE conditions. The driver learns his car's brakes and road conditions and can make adjustments optmizing for the conditions. I run a static balance bar on one of my hot rods and it works GREAT. However it is static - which means I highly doubt it fares as well compared to a similar setup that had a proportioning valve that is in non-optimum conditions - like rain. In my case I don't run this particular car in the rain (at least not very often) so I live with that downside - although I recognize it is there and am aware of it when conditions aren't optimal. The rest of my rides I run proportioning valves - they are more likely to get caught in the rain and therefore it makes more sense to me.

Quote:
Originally Posted by ago View Post
Hey Guys what about a system that is used on race cars. 2 separate M/C and

a adjustable pivot point at the brake clevis?



Ago
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Old 02-13-2010, 11:31 AM   #54
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Default Re: Proportioning valve delete

Adjustable is probably best in your case. I don't believe the factory proportioning valve influences the front pressure unless you're talking about the holdoff valve in a disc drum setup - and that is out of the equation after 200 psi anyways so it is YOU the driver setting the front brake pressure via your foot - the proportioning valve changes the rate of pressur edrop to the rears to compensate for changing tire load (as a result of weight transfer) - this rate is calculateds by the factory as they consider all the variables - so unless you can find a factory set up that is VERY close to your own - the prest value is probably not right for you. That is why the aftermarket ones are adjustable - you can ideally dial it in to optimize your particular set of conditions.

Quote:
Originally Posted by henryj429 View Post
And another question:

What's a better choice for a hot rod (4 wheel disc in my case) - late model OEM proportioning valve or Wilwood style adjustable type that goes in the rear line?

The OEM valve can influence both front and rear pressure (or the balance thereof) while the Wilwood can only lower pressure to the rear. I like the adjustability that the Wilwood provides, but can it work as well for brake balance without any reference to the front line pressure?
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Old 02-13-2010, 05:15 PM   #55
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Default Re: Proportioning valve delete

Essex 29 it doesn't look like you can simply disable the OEM valve without losing the the pressure differential switch as well so you'll only be left with the metering function

HemiRambler the point which the valve begins to throttle pressure is static on this type and dynamic on height sensitive types.

Bill vacuum diaphragms are sometimes called servos so I don't know what you mean by servo brakes or differentiate between them and power brakes.

-another hobbyist

Last edited by ehdubya; 02-13-2010 at 05:19 PM. Reason: typo
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Old 02-13-2010, 06:08 PM   #56
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Default Re: Proportioning valve delete

Quote:
Originally Posted by ehdubya View Post
Bill vacuum diaphragms are sometimes called servos so I don't know what you mean by servo brakes or differentiate between them and power brakes.

-another hobbyist
"Servo" brakes are the self energizing design introduced in the '30's (I think) that allowed for more self energizing than inherit in drum brakes. I think they allowed for a 4:1 increase, meaning they increased the braking effort 4 times over the effort put into the pedal. They were very effective for a stop or two and allowed big cars to be stopped by little people, but they had problems. Because the servo increase depended on friction between the shoe and drum, as the brakes got hot and lost effectiveness, the servo went away. Just when you really needed it! Also, when backing, the servo function reversed, so you had 1/4 the braking power or 1/16 of that when going forward.

When vacuum assist power brakes came along, there was no longer a need for the servo, but the industry stayed with it, I think mostly for parts interchangability. Then power front disc brakes came along and some manufacturers (GM, at least) kept the servo brakes on the rear, leading to the stepped pressure proportioning valve and the myth that proportioning valves are needed for any good disc/drum system.

Bill
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Old 02-13-2010, 06:38 PM   #57
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Default Re: Proportioning valve delete

thanks, I found this explanation
Quote:
Drum brakes are divided into two main categories

1. Simplex brakes

The brakes consist of a primary and a secondary brake shoe. Which shoe is which depends on the braking direction. The primary shoe takes up most of the torque and its lining therefore wears fastest. Braking often in one direction results in different degrees of wear to the brake shoes.
Each brake shoe is attached at its bottom end to a separate fixed pivot attached to the backing plate.
99% per cent of mechanical brakes are simplex brakes.
The wheel cylinder is bolted in place, but does not take up any forces.
One way of transferring force at the top of the shoes is to use a wheel cylinder with two separate pistons, each pushing outwards on its own brake shoe.
One or more external return springs pull back the shoes to release the applied braking torque.
Simplex brakes are cheaper to manufacture than servo brakes, the design is lighter and changes in friction are not amplified.

DUPLEX – a variant of Simplex brakes

DUPLEX brakes are able to handle a slightly higher braking torque.
In principle there are two primary brake shoes.
There is a separate wheel cylinder for each shoe, and the rear of the wheel cylinder acts as a stop. Each brake shoe is naturally attached at its bottom end to a separate fixed pivot attached to the backing plate, a distinguishing feature of Simplex brakes.

2: Servo brakes

Each brake shoe is linked to the other and the brake shoes are floating. The torque is taken up by a wheel cylinder or mechanical stop.
Servo brakes must not be fitted to steering front wheels since the braking action can vary depending on external conditions. This design is sensitive to variations in the coefficient of friction.
Servo brakes are self-amplifying.
Higher torque than simplex brakes for the same size of wheel cylinder.
Servo brakes are generally chosen for slow-moving vehicles that do not travel faster than 30 km/h, but they should not be ruled out for faster vehicles.
More expensive to manufacture than simplex brakes and a more complex design.
Typical applications: Heavy vehicles, fork lift trucks, used on trailers at speeds in excess of 30 km/h.
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Old 02-13-2010, 09:22 PM   #58
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Default Re: Proportioning valve delete

I thought the idea of a pro-valve was to allow the rears to brake without locking up. To say that the rear brakes are working correctly just becuase they don't lock up... maybe they are not working enough to give you max stopping power. I did this. I did a few panic stops on gravel and then compared the skid marks to see if the rears would lock up - then I went wet pavement and did it there. Finally the dry black top... be ready to nose the windshield. ( why is it so easy to burn rubber going forward but so mentally hard to "slam" on the brakes and skid to a stop... is for me?

Anyway.. I think a pro-porotioning valve is the way to go and a lot of testing to get it safe.
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Old 02-13-2010, 11:13 PM   #59
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Default Re: Proportioning valve delete

ehdudya, That explanation may be true in other countries, but not here in the US. Since the 70's (even earlier) the US cars have most all used DUAL SERVO FRONT and REAR. There are some exceptions ( I think AMC) was one where they used single servo rear with disc in front.

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Originally Posted by ehdubya View Post
thanks, I found this explanation
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Old 02-14-2010, 02:54 AM   #60
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Default Re: Proportioning valve delete

Since the original question in this thread reamins unanswered, I'll answer it myself.
Here's what came out of my proportioning/combination valve.
I had tried to disassembled it once, but failed, but juggling long enough with it had the yellow green piston in the pic, come out, bringing the rest with it.



I took a pic, and added some drawn parts to make it more illustrative.


Regarding brakes needing a proportioning valve to compensate for weight transfer: Not true.
Front brakes are made with bigger pistons, greater diameter or wider linings, and therefore more braking power is generated with the same pressure.
Proportioning valves are used to fine tune brakes to different applications, such as longer shorter wheel bases, heavier or lighter engines etc.

I have no proportioning valve on my Essex hot rod, and use Plymouth drums on all wheels. The fronts still lock up way before the rears. This is not a problem, since it's not driven at ballistic speeds. But it illustrates my point.
It would actually need a proportioning valve on the front brakes.
Chew on that
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Old 02-14-2010, 03:05 AM   #61
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Default Re: Proportioning valve delete

Come to think of it, the short wheel base Morris/Austin Minis used a brake limiter, so no matter how hard you pressed the brakes, a man could turn the rear wheels without too much effort.

Morris Mini 1275 GT

Guess this contradicts my earlier post a bit, but no rules without exceptions, eh?
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Old 02-14-2010, 07:59 AM   #62
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Essex_29, I am sorry but I disagree. I tried to explain this before and I propably used poor wording as I am not an expert on the subject terminology. I totally understand the concept that the fronts are built differently than the rears - meaning we can & do have varying braking power out of each end (front versus rear).

If I take your statement at face valve ( the part about the Porportioning valve being used soley to match components because of various build conditions engine weight , wheelbase etc) then how do you explain the CURVE on my graph picture???? The if this is a STATIC problem and all the factors you mention are constant then the relationship between front and rear are LINEAR. This in reality is NOT LINEAR - at least not linear IF you are trying to optimize your brakes at various braking "g" load conditions. The relationship changes - ie NOT LINEAR. The proportioning valve attempts to duplicate this curve in a best fit arrangement.

I'm sorry your point is NOT illustrated because the "problem" is not about driving at ballistic speeds - it is about varying conditions meaning trying to optimize balance at an entire range of braking pressure. Please look at the graph I posted earlier - notice the straight line illustrating the relationship between front and rear - changing components be it brakes vehicle weight cg etc won't change the fact that that line is FLAT. There is nothing DYNAMIC there. It is that shift in weight - which is of course different depending on how hard you brake that the proportioning valve is trying to compensate for. We always hear the statement that the front brakes do 75% of your braking - well as true as that statement is it is also slightly misleading. I refer to my origional fictional example of the car with all identical components & the perfect 50/50 weight split -Let's pretend we are approaching a stop and initially hit the brakes ever so lightly - under the lightest of braking conditions let's say there is NO weight transfer and therefore each tire is capable of supporting the exact same amount of braking capability. we would want the same brake pressure to both halves of our system. Notice the very beginning of our graph - it shoots up at a 45 degree angle - symbolizing equal pressure in both haves of the system. As we are approaching out stop we determine we are still going too fast and apply a little more pressure to our brakes. At this point we are experiencing some weight transfer (let's pretend it shifts from 50/50 to 60/40 - the result of the transfer means our front tires are carrying more dynamic load - the result (see note 1 below) is that it can now support more braking force before lockup than before - this is no problem for the fronts because under a mild condition we are still well within the limits of traction however for what we GAIN in the fronts ability to stop we also LOOSE in the rears (no free lunch) - this is where the problem begins. The solution is to reduce the pressure to the rear brakes to prevent lockup. So now EACH wheel is MAXIMIZING their ability to stop. AS we continue on we are noticing we are still going too fast and apply even MORE PRESSURE to the brake pedal. AS before the result is even MORE weight transfer now let's say it goes from 60/40 to 70/30. Just as before - the fronts having MORE LOAD can do more stopping - and also the rears can do LESS - again we must do something to address this - which as before is to drop the pressure to the rears even "more". And by "more" I mean it is even further from the LINEAR LINE than previously - so in anotherwords we haven't really dropped the rear pressure because in realality it is still increasing - what we have "dropped" was the RATE of pressure rise. Again let's refer to the graph - that curve is falling off quickly. These are varying conditions - we need to address them in some manner IF we want to optimize the system. So now granted we can design a system without a proportionign valve that is balanced at any single pressure point - however at the remaining points we will be "off" further from deal than IF we chose to use the proper proportioning valve.
Now to adress your points about longer wheel bases and heavier motors etc etc. these all shift the CG of teh vehicle and YES I agree this certainly has an effect on the proportioing valve as it affects the WEIGHT TRANSFER.

Note 1 - For years Drag Racers were always trying to maximize weight transer. The reason being that they realized to carry weight is a penalty - so making the cars lighter made them faster, but when they were restricted to a "small" tire they quickly realize that shifting as much weight to the rears tires on launch as possible they could also MAXIMIZE traction without adding overall weight to the vehicle . More tire load = equals more traction --> much the same way that weight shift forward means more tire load and increased brake ability.


So my question to you is simple - if not the proportioning valve - how DID the factory deal with weight transfer?? Did they simply ignore it???? Did they design for one and only one braking pressure to be optimized?? What 's the scoop???


EDIT: Since I was asked earlier for some "supporting documentation" and I did my best to comply (sorry those pics aren't all that great - if anyone is interested I can scan them next week and repost them so they are more legible) - what I now ask back is for all those saying I am full of crap - please do the same - I would love to see YOUR REFERENCES. If I have totally misunderstood my reference material I would appreciate some additional material so we can all get down to what's what. So far we've only had one and it wasn't very applicable to what is "common" in the US - especially the part about dual servo being only good for things like tow motors!! ha ha

Essex_29 You're right we did neglect to answer your origional question. So the answer is "yes".

Quote:
Originally Posted by Essex_29 View Post

Regarding brakes needing a proportioning valve to compensate for weight transfer: Not true.
Front brakes are made with bigger pistons, greater diameter or wider linings, and therefore more braking power is generated with the same pressure.
Proportioning valves are used to fine tune brakes to different applications, such as longer shorter wheel bases, heavier or lighter engines etc.

I have no proportioning valve on my Essex hot rod, and use Plymouth drums on all wheels. The fronts still lock up way before the rears. This is not a problem, since it's not driven at ballistic speeds. But it illustrates my point.
It would actually need a proportioning valve on the front brakes.
Chew on that
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Old 02-14-2010, 09:23 AM   #63
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Default Re: Proportioning valve delete

HemiRambler, that brings me back to my earlier question. The Wilwood adustable valve has only one setting which probably will work best at one level of braking pressure and not as good at all others. An OEM valve - according to your very good discussion - should work well over a much wider range of braking conditions, except that it is optimized for a certain vehicle and could actually work badly when put on a car with different brake hardware, weight distribution and tires.

So, for a hot rod that is a one of a kind vehicle, is the Wilwood the lesser of two evils?
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Old 02-14-2010, 10:12 AM   #64
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Default Re: Proportioning valve delete

Henryj429 - that's a good question that leads us to discuss how the proportioning valve actually works. I hesitated to mention this before because I was afraid to muddy the discussion (fat chance - I know). Ideally we have a curve on our front to rear pressure graph. The proportioning valve doesn't magically duplicate this ideal curve - in actuality it can only be adjusted for a "best fit" scenario by changing the crossover or rather the Changeover Pressure point. See the attached photo. The dashed lines represent the actual pressure relationship out of the proportioning valve - notice in each example (the 60/40 and 50/50) both rates for the proportioning valve are the same. By the same I mean they change at the same rate - ie the 2 "slopes" are the same. So what we are adjusting is not those rates - although it'd be nice to - instead we are adjusting the point at which we changeover from one rate to another - trying to get the combination of those two straight lines to fit as best we can to the actual curve which represents the ideal braking condition.

So it is quite possible in theory that a factory proportioning valve can have a different rate as well as a different changeover pressure - so maybe just maybe it could outperform an adjustable valve in some particular application. I think those are slim odds, but possible nonetheless. The adjustable one while far from ideal at least gives you the ability to "tweak" the realationship for a BEST FIT scenario.
And just for the sake of discussion - please note these graphs are all in relationship to the "G" force. Sorta makes a fella wonder why?(hint hint for those who still think I am clueless) Also notice this example talks about the CARS WEIGHT being 50/50 and 60/40 - not the brakes doing 50/50 or 60/40 - obviously because that pressure relationship is changing as represented by the "curves".


So the "one setting" we are talking about is in fact correct - depending on how you look at it. So it isn't really that "one setting" it's the various settings allowing us to shift our straight lines around to best fit our car's particular ideal curve. Without a proportioning valve the equation simply gets worse and worse as you go - represented by the initial actual pressure line continuing linear and getting further and further from that ideal curve.

So in some sense of the word - calling the proportioning valve dynamic may be a bit misleading - what is dynamic is the brake bias versus the "g" force. So as the "g" force changes so does our ideal situation. The answer is dynamic - so tossing it (the proportioning valve) is about as useful as the aussies description of a tosser - it may make you feel good for a few seconds, but long term you accomplished very little.

The factory proportioning valves are mostly combination valves - which simply adds multi purposes to one valve - I don't know enough about the rates and changeover points to say one is better than another across the board - at least when you are comparing apples to apples. For all I know they have the same rate - and in THAT case for a Hot Rod - the adjustable one makes more sense as I can tweak my "curve" to be as close as possible to the ideal. Now IF you have a situation where your rod duplicates a factory setup very closely - then unless you are REALLY dedicated & determined to find the "sweet spot" on your adjustable proportioning valve in THAT particular situation the factory valve may very well be the best bet. And in THAT case you get the added bonus of (assuming you're really using a combination valve) it's other features.

Remember that "one setting" has adjusted more than just one pressure point.

Does that make sense???

Quote:
Originally Posted by henryj429 View Post
HemiRambler, that brings me back to my earlier question. The Wilwood adustable valve has only one setting which probably will work best at one level of braking pressure and not as good at all others. An OEM valve - according to your very good discussion - should work well over a much wider range of braking conditions, except that it is optimized for a certain vehicle and could actually work badly when put on a car with different brake hardware, weight distribution and tires.

So, for a hot rod that is a one of a kind vehicle, is the Wilwood the lesser of two evils?
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Old 02-14-2010, 10:20 AM   #65
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Default Re: Proportioning valve delete

HemiRamler, I think you are correct in that the early GM valves with delayed proportioning were an attempt to optimize braking effort across the spectrum of braking conditions. But why? You increase rear braking effort under "normal" conditions when maximun controlled stopping is not the issue. Nintey percent of the time you really do not need the extra braking effort, all you gain is a small amount of front brake wear transfered to the rears.

Also, the system is not dynamic in the sense it can react to current driving conditions. Put three people in the rear and a hundred pounds of salt in the trunk the braking split remains the same. The factory proportioning valve configuration is valid only when using factory spec components. Swap the front pads for some high performance items and the whole optimizing thing is out the window. For all its sophisication, the GM system was not adaptive to anything.

Bill
P.S., I note you addressed most of this while I was typing.

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Old 02-14-2010, 12:23 PM   #66
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B Blue, I think you are right again.
The ideal brake bias may be a curve, but the only time we really need that braking in exact proportions is when braking as much as is possible, ie when the wheels are locking up.
This is also evident whan we drive on slippery surfaces, as snow. With almost no weight transfer, the fronts lock up real easily, and you need to press real heavy on the pedal to lock up the rears.

HemiRambler, You may be right about a proportioning valve being very important on production cars, but oddly enough the '68 Plymouth Satellite I robbed my brakes off didn't have one...

Thank you for answering my original question.
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Old 02-14-2010, 12:42 PM   #67
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B Blue, I think the "why ?" wasn't nearly as much about pad wear as it was about ROAD CONDITIONS. On a slick surface you cannot stop as hard or you skid - so with LESS pressure to the fronts and therefore less weight transfer you can ADD (or not reduce as much) pressure to the rears when they CAN handle it - thus optimizing your braking under adverse conditions. Driving in the snow I get to experience this quite a bit. So I agree it ISN'T all about maximum stopping under ideal conditions - it is very much about that darn grey area in between!!!!

With that in mind - I can see a system with no proportioning valve and matched components stopping under ideal conditions in some number of seconds or feet or what have you. Now near exact duplicate system WITH a proportioning valve and a rear brake capable of slightly more braking power - viola - it stops in exactly the same time and distance. No improvement - the excess rear power was too much and thus reduced by the proportioning valve. Does this prove you don't need a proportioning valve - (well to some I am sure it does - they argue that they matched their components "better" and eliminated this un-necessary part) and if ALL your braking is under this ideal set of conditions then I suppose you can make that arguement. This BTW is similar to the balance bar example I mentioned earlier. So with this example in mind - can we call these systems "equal" - I would say SURE, BUT!!!! (you knew this was coming right?) only under this one set of circumstances. So now same two vehicles - panic stopping in the rain - the proportioning valve system at this lower "G" load has the ability to INCREASE the REAR BRAKE pressure over it's non-proportioning valve counterpart. The proportioning valve car's rear brakes due to less weight transfer can carry "extra" brake load and thus THAT car stops better/shorter/quicker. Reduce the overall braking conditions even more and maybe you get below that changeover pressure and again the systems are equal in performance again. So can one make the arguement - it's not enough to matter - sure - I personally am not buying it, but to each their own. I also like to look at it this way - GM can and did match their components - they also got rid of 2 cent grease fittings and yet kept the proportioning valve. Why??? I can tell you one thing it wasn't public awareness!!!!!!! They kept it because it served a definite purpose.

I agree to the point about it not being dynamic in the sense you describe - the system has no idea whether you have 1 passenger or 5 - but with 5 you DO have more weight - with more weight you get more weight transfer - and with that additinal transfer you get more brake potential from those front tires - effectively meaning you are simply operating FARTHER up the pressure curve - so now with more load - you are hopefully closer to optimizing than with out it. Now clearly - this is somewhat limited - the only truely dynamic proportioning valve are the ones I mentioned earlier the ones that were used in some pickup trucks - those sensed ride height (due to load) and adjusted the proportioning valve accordingly. So yes I agree and admit that the pickup truck example is not normal or even very common. I probably misused the word dynamic - but I was trying to emphasize the part about the pressure curve being non-linear.

Yes the GM system was NOT ADAPTIVE - I didn't mean to suggest it was - rather it was designed to adapt to those changing conditions - once set - it didn't ever change that relationship - instead YOU the driver changed how hard you depressed the brakes - the only thing remotely "adaptive" was how it changed the rate of pressure drop. And YES I realize that was truely static. I suppose I chose some poor words - but what I was trying to emphasize was that the brakign conditions CHANGE with load and this system changed with YOUR LOAD - granted it did the same change everytime so calling it dynamic was probably confusing - I just don't have a better grasp of the english language to have come up with better more accurate and descriptive words.


Quote:
Originally Posted by B Blue View Post
HemiRamler, I think you are correct in that the early GM valves with delayed proportioning were an attempt to optimize braking effort across the spectrum of braking conditions. But why? You increase rear braking effort under "normal" conditions when maximun controlled stopping is not the issue. Nintey percent of the time you really do not need the extra braking effort, all you gain is a small amount of front brake wear transfered to the rears.

Also, the system is not dynamic in the sense it can react to current driving conditions. Put three people in the rear and a hundred pounds of salt in the trunk the braking split remains the same. The factory proportioning valve configuration is valid only when using factory spec components. Swap the front pads for some high performance items and the whole optimizing thing is out the window. For all its sophisication, the GM system was not adaptive to anything.

Bill
P.S., I note you addressed most of this while I was typing.
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Old 02-14-2010, 12:56 PM   #68
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Default Re: Proportioning valve delete

Essex - absolutely agree LOTS of production cars did NOT have porportioning valve - brake systems have been refined to work better and better every year since their inception. Do you think that '68 Plymouth will stop as good as the latest hardware on the road today? Apples and oranges I know, but therein lies the problem - we ARE using older less sophisticated hardware than those around us - they have their antilock this and computer that etc etc. We are already at a disadvantage - plain and simple. Why would you give away even more???? I don't want a computer in my car - I'm not even suggesting that - I am only saying why not make your system as optimal as possible?? May save you some grief in some extreme downpour someday.



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Originally Posted by Essex_29 View Post
B Blue, I think you are right again.
The ideal brake bias may be a curve, but the only time we really need that braking in exact proportions is when braking as much as is possible, ie when the wheels are locking up.
This is also evident whan we drive on slippery surfaces, as snow. With almost no weight transfer, the fronts lock up real easily, and you need to press real heavy on the pedal to lock up the rears.

HemiRambler, You may be right about a proportioning valve being very important on production cars, but oddly enough the '68 Plymouth Satellite I robbed my brakes off didn't have one...

Thank you for answering my original question.
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Old 02-14-2010, 02:29 PM   #69
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Essex 29, you're right, 4 wheel drum bias is proportioned by wheel cylinder and lining area but all drums are self energizing to some degree in that when the linings contact the drum they wind out so pedal effort is not directly relative to braking force like disc brakes which have different pressure requirements.

Quote:
Originally Posted by HemiRambler View Post
Since the 70's (even earlier) the US cars have most all used DUAL SERVO FRONT and REAR. There are some exceptions ( I think AMC) was one where they used single servo rear with disc in front.
I think what you're describing they define as Duplex. I'm curious what specific pre vacuum assisted vehicles Bill mentioned used Servo brakes as I've never encountered them.
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Old 02-14-2010, 03:50 PM   #70
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Default Re: Proportioning valve delete

I believe what I've called servo brakes is really Duplex, which employ a servo action to magnify the braking effort.

Bill
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Old 02-14-2010, 08:11 PM   #71
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I'm not sure & I wondered the same thing initially because it sounded so bizzare so I read and reread it several times. What "they" wrote was quite confusing. Their version of duplex I could see as described as a DUAL SERVO but as described earlier would work crappy when rotated in reverse as you loose all servo action in that direction. I think I even added to the confusion because what I was describing as DUAL SERVO was what Bendix called DUO-SERVO which is what I think they called "servo" which again they went on to describe som ebizzare stuff like NOT using that for steer wheels and better suited for slow speed two motors.

The real confusing part is that ALL DRUM brakes exhibit some SERVO ACTION - the question is how much. An old style single wheel cylinder bottom pivot twin shoe drum brake setup has one shoe leading and one shoe trailing - with ONLY the leading shoe benefitting from servo action (well when rotated in one direction anyways). I called this "single servo" but I think the proper term or at least the more common term is "leading and trailing Shoe" brakes.

The Duplex version they had - I didn't even consider but can see how it could be thought of as DUAL Servo - since you can arrange both shoes to benefit from servo action in one direction but neither shoe benefits from it in the opposite direction.

And what they called SERVO - I STILL (mistakenly?) think of as DUAL SERVO - but in reality Bendix Called DUO SERVO and was set up with a single wheel cylinder - NO shoe pivots - but floating shoes connected to one another and anchored in place by a large pin. In one direction you get both shoes to work together as they become one due to the connector link (aka adjuster link or self adjuster)- These get forced into (or better stated wedged into place)on one side of the anchor pin while the opposite side pushes away from that same pin. The entire operation is reveresed when the drum is rotated the opposite direction and therefore works very well in BOTH directions - giving you all the benefits of dual servo action and no reversing penalty. Clearly it was THIS setup they described so goofy. They also went on to say that most mechanical brakes (99% IIRC) were SIMPLEX - which must date this either to WAY WAY BACK or simply so different from teh stuff we use in the states that I can't even fathom it.

So anyways - YES - whenever I wrote DUAL SERVO - what I really meant was the Bendix DUO SERVO and not a twin wheel cylinder twin shoe pivot getup.


The really confusing part is the servo description - since they all benefit a certain degree from servo action - it is just plain confusing to say some are servo and some are not. They pretty much all are - just to different degrees - - let me frame that comment is about DRUM BRAKES!!!


Quote:
Originally Posted by ehdubya View Post
Essex 29, you're right, 4 wheel drum bias is proportioned by wheel cylinder and lining area but all drums are self energizing to some degree in that when the linings contact the drum they wind out so pedal effort is not directly relative to braking force like disc brakes which have different pressure requirements.


Originally Posted by HemiRambler
Since the 70's (even earlier) the US cars have most all used DUAL SERVO FRONT and REAR. There are some exceptions ( I think AMC) was one where they used single servo rear with disc in front.

I think what you're describing they define as Duplex. I'm curious what specific pre vacuum assisted vehicles Bill mentioned used Servo brakes as I've never encountered them.
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Old 02-15-2010, 06:22 AM   #72
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yay, we're all on the same page! Yeah the terminology sure is confusing, let's hope Essex 29 gets some good brakes.
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Old 02-19-2010, 03:13 AM   #73
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Thank you Hemi Rambler for a lot of interesting and inspiring info on brakes, prop valves etc. I've been looking for info on drum brakes on the net, and there's lots of designs!
This is what I found on what you call Dual Servo Brakes:

"Duo-servo:A drum brake that has servo action in both the forward and reverse directions."

That name makes sense.

Never mind the name, Any case it's that kind of drumbrakes I have under my cars.
The '68 Heavy duty 11" dia and 3" wide Mopar drum brakes are fine on my light weight Essex. They're not as good as some newer brakes, but as I'm sure lots of people building rods do, I chose them because they look cool.

But that's another thing, and another car.
The reason for taking out the internals from my proportioning valve is that the Ford rear drums seem to need more pressure than the GM drums once plumbed in the same place. The reason not to replace the prop valve is that I don't know for a fact that deleting the prop valve will get me enough pressure to the rear brakes.
If this is the case, a proportioning valve will do no good before the rear brakes are rebuilt with larger diameter brake cylinders.

As you may have seen in a previous post of mine, I have now deleted the valve by taking out the internals, and when some other work is done, and the brakes bled, I'll go for a test drive, maybe take it to a brake dyno, and I'll post the results. It may be a while though, because we have winte and snow and 20 below freezing... BRRRRRR!

Haven't anybody tried to adapt a Ford 9" with drum brakes on a GM car, and had this problem with weak rear brakes?
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Old 02-19-2010, 03:13 AM   #74
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Thank you Hemi Rambler for a lot of interesting and inspiring info on brakes, prop valves etc. I've been looking for info on drum brakes on the net, and there's lots of designs!
This is what I found on what you call Dual Servo Brakes:

"Duo-servo:A drum brake that has servo action in both the forward and reverse directions."

That name makes sense.

Never mind the name, Any case it's that kind of drumbrakes I have under my cars.
The '68 Heavy duty 11" dia and 3" wide Mopar drum brakes are fine on my light weight Essex. They're not as good as some newer brakes, but as I'm sure lots of people building rods do, I chose them because they look cool.

But that's another thing, and another car.
The reason for taking out the internals from my proportioning valve is that the Ford rear drums seem to need more pressure than the GM drums once plumbed in the same place. The reason not to replace the prop valve is that I don't know for a fact that deleting the prop valve will get me enough pressure to the rear brakes.
If this is the case, a proportioning valve will do no good before the rear brakes are rebuilt with larger diameter brake cylinders.

As you may have seen in a previous post of mine, I have now deleted the valve by taking out the internals, and when some other work is done, and the brakes bled, I'll go for a test drive, maybe take it to a brake dyno, and I'll post the results. It may be a while though, because we have winter and snow and 20 below freezing... BRRRRRR!

Haven't anybody tried to adapt a Ford 9" with drum brakes on a GM car, and had this problem with weak rear brakes?
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Old 02-19-2010, 04:39 PM   #75
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Default Re: Proportioning valve delete

A couple of things really should be addressed, clarified and corrected. I'm not going to quote the incorrect information, as it has been repeated several times. Also, several magazine articles, as well as some internet info, are just wrong on some of their content.

1-Drum brakes. There are two basic designs, servo and non-servo, period. When the shoes are isolated from each other, there is NO servo action, whether a fixed or sliding anchor design, and therefore are non-servo brakes. These can be found on most early cars/trucks, early Fords up to '48 (Lockheed) and on the rear axles of many late model front-drive, and a few rear drive vehicles. The fixed-anchor designs are not as efficient as sliding anchor designs, but they are all non-servo in operation.

Bendix brought out the Duo-Servo drum brake in the late 30's, and it became standard on all Fords in '49 as well as many other makes, and, along with design variations made by other manufacturers, are still used today on the rear axles of many cars and trucks. Both shoes use a single common upper anchor, while being connected or linked together at the bottom by the adjuster. When the vehicle has forward motion and the brake is applied, the forward ( primary) shoe "serves" the rear (secondary) shoe through the adjuster, forcing the secondary shoe into the drum and back into the wheel cylinder. This "servo" action makes the brake much more effective than non-servo designs, along with requiring less system pressure and/or pedal effort. (Ford cars and light trucks, along with many other cars, did not need power assist until after the early 50's)

There is/was also a Uni-Servo brake, found mainly on boat trailers with hydraulic actuation. These have one forward-acting cylinder, resulting in good forward servo braking, but down to about 10% while backing up, to ease launching.

The only disadvantage of a Duo-Servo brake is complexity, and cost. Duo-Servos usually have different length and/or material pri/sec shoe linings, along with sometimes complex self adjuster assemblies, whereas non servos usually have common shoe/linings and simpler adjusting mechanisms, which makes them easier to manufacture, assemble, warehouse and install.
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Old 02-19-2010, 06:12 PM   #76
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Default Re: Proportioning valve delete

Proportioning Valves- PV‘s for short.

PV's became necessary because of the higher line pressure required for disc brakes. Their purpose is to limit pressure to the rear brakes. There are several kinds; ie, fixed, load sensing and inertia, which are mechanical, and the later electronic PV's incorporated into ABS systems. I will keep the discussion to the fixed style, like most of us use or are familiar with, such as the Wilwood, and older Bendix and Kelsy Hays stand-alone valves.

Front disc brakes became popular in the late 60’s, and standard fare by 1975 or so. The problem was there was not universal brake test requirements or standards until FMVSS “105-75” was adopted in the mid 70’s. Up to that point, a few states had tough lining requirements, Pennsylvania being one of the toughest, and most manufactures made sure their vehicles passed these independent state requirements. But it wasn’t until 105 testing became mandatory that vehicle brake systems became more refined. This is one reason why PV’s were not on all early disc-brakes vehicles.

The “105“ (and newer “135”) tests require all vehicles to meet stopping distance requirements at loaded GVW and LLVW weights, full and partial braking systems (failing each half of the master cylinder), failing any assist (ie, vacuum ), several dry and wet fade tests, and parking on a 30 % grade. In a common vertical-split brake system (front axle/rear axle, as apposed to a typical front drive “cross” split LF/RR & RF/LR), the rear brakes have to be large enough to stop the vehicle within the required stopping distances, loaded and LL, from 60 MPH, and hold the vehicle on a parking grade, up and down for 5 minutes, along with all the other tests the vehicle has to perform. Now maybe you can understand why PV’s are necessary. If you knew how much test time was needed to match PV’s to each vehicle, with all the various wheel base, tire, front/rear weight change, engine size, weight capacities, etc, you would understand why using a factory or aftermarket “fixed” PV’s either alone or as part of a combination (combo) valve is a crap shoot at best!

The PV's operate by allowing system pressure to be equal to all brakes until the "crack", "split" or "knee" point has been reached, and then reduces pressure out of the PV based on a pre-set fixed percentage, rate or ratio. Common rates are .27, .43, .59 and several others. If we take a .27 valve, with a “crack” point of 500, all pressure will stay equal to 500 psi, then the PV will limit the rear pressure at a rate of .27, or 27% of every additional 100 psi delivered to the fronts. So at 600 psi to the fronts, the rears will see 527; 700 fronts = 554 rears; 800 fronts = 581 rears; 900 fronts = 608 rears, and 1000 to the fronts = 635 to the rears. Important to note- these values are the same static or dynamic with a fixed PV, and the rear pressure never reaches the front pressure value after the crack point. Usual max crack pressure is about 1000 psi, so the adjustable Wilwood or similar will allow equal pressure up to this value with the knob screwed/turned to max.

Bob

Last edited by V8 Bob; 02-19-2010 at 09:05 PM.
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Old 02-19-2010, 11:21 PM   #77
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Default Re: Proportioning valve delete

Bob, It appears that my reference material contradicts your comments - Could you please elaborate on exactly what and HOW servo action is achieved.

Also how does the mechanics of the Boat example you cited below work???

EDIT: actually my reference material divides the drum brakes into 3 categories: Leading/trailing shoe, two leading shoe & duo-servo (while they do show examples of tri-leading shoe - it's basically a derriviative of the two leading shoe and therefore isn't "different" enough to make another category out of it)

Anyways - in the 2nd picture (I just added) they are comparing the 3 main types of shoe arrangements to see how each one's differing SERVO ACTION affects PEDAL EFFORT. So again the material more than suggests each design benefits from servo affect - it plainly shows the results.

I think as the dsigners understood this relationship and started to rearrange components to take advantage of it - they also started to use the terms - and at THAT time some were referred to as "servo" brakes while other (older) designs were maybe not so much, but to suggest some have it while others do not is really muddying the waters. IMHO

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Originally Posted by V8 Bob View Post


1-Drum brakes. There are two basic designs, servo and non-servo, period. When the shoes are isolated from each other, there is NO servo action, whether a fixed or sliding anchor design, and therefore are non-servo brakes.

There is/was also a Uni-Servo brake, found mainly on boat trailers with hydraulic actuation. These have one forward-acting cylinder, resulting in good forward servo braking, but down to about 10% while backing up, to ease launching.

Bob
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Old 02-20-2010, 08:02 AM   #78
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Default Re: Proportioning valve delete

HemiRambler,
I tried to explain the difference between servo and non-servo above, so I'm not sure what else I can add that would make it more understandable. The picture you show is a fixed anchor non-servo brake, plain and simple.

There have been several names for various designs of non-servo brakes over the years. Some have one cylinder, some have two, along with fixed and sliding anchors, but the fact is, if the shoes do not interact with one another, they are non-servo. As I stated early on, there is a lot of mis-information on the net and published. I found one article on the net stating how to adjust a Bendix Duo-Servo, when in fact they were describing a Lockheed-design fixed anchor shoe adjustment! Go figure!

The graph you presented shows the effectiveness difference of:

1-single cylinder non-servo or single-leading; the least effective.

2- twin cylinder non-servo or two leading, more effective, usually found on heavy cars and light-med. trucks, and

3- Duo-Servo, king of the hill in drum brake design.

The Uni-Servo trailer brake was/is used with hydraulic surge hitchs-the hitch telescopes and operates a master cylinder during vehicle braking (trailer dynamic inertia) but also while backing the trailer (trailer mass). The brake has a single piston cylinder that pushes the forward or primary shoe, which then serves the secondary through the adjuster, and provides near-duo servo performance forward, but has very little braking going backward, without the need to lock out the surge master. Later hydraulic disc equipped trailers with surge hitches use a backup-light-operated fluid (or other) lockout that effectively makes the hitch “solid” and allows easy backup without trailer brake apply.

I agree with your last statment that design names get lost, mixed or confussed over time, intentionally or otherwise. What bothers me most are some of the statements made by people in the aftermarket brake supply business that can make some really nice adaptors, brake kits, pedal/cylinder assemblies, etc, but don't have a clue on how some of the products they sell actually work!

Bob
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Old 02-20-2010, 09:10 AM   #79
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Default Re: Proportioning valve delete

Combination Valves-One more item that needs clarification.

Combo valves became standard issue in the 70's through the 80's on most vehicles. They usually contain the prop valve (PV), metering (hold-off) valve, and pressure differential switch (diff. switch), although some only have the PV and diff. switch.

The PV has been discussed above so we'll pass on that for now.

Metering, or hold-off, was used through the 70's on and off until the 90's on disc/drum vehicles, mostly cars. Their purpose is to hold off the front disc brake pressure until the rear drum brakes reach about 100 PSI. The theory was that by allowing the drum shoes to overcome the strong return springs, shoe-to-drum contact would occur at the same time the front pads contacted the rotors, providing "even" braking. Sounds good, and worked Ok for some vehicles. The problem was that the rears could become too aggressive, promoting early rear slide during performance stopping distance testing, a big NO NO. The DOT "105" requirements allowed only one wheel to slide above 10 MPH. If you are backing off line pressure to keep a rear from sliding, the stopping distance will be longer, and possibly "blow" the stop by exceeding the requirement. So the metering valves disappeared for awhile, then came back in the 90's on a few vehicles because "pedal feel" and "benchmarking" became very important. Thankfully, ABS became the norm and did away with the need for metering and PV's! You really don't want one of these on your custom brake system, as it could cause early rear slide, and you want to avoid rear slide at all costs.

The pressure differential switch was simply a shuttle switch that turned a failure light on in the dash when there was a system pressure difference of about 400 PSI or more. Of course, this applies to 1967 and up dual brake systems. This switch has NO effect on braking-it just lets you know if you have a serious pressure problem.

It's not a bad idea to use a diff switch (newer masters with non-metal reservoirs have built-in float switches that monitor fluid level) but using a new or especially a used combo valve is not a good idea. Keep it simple by using an adjustable PV with a disc/drum system, along with necessary residual valves. It's easier to plumb in a PV and not need it vs having to add one later.

Bob

Last edited by V8 Bob; 02-20-2010 at 10:03 AM.
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Old 02-20-2010, 01:34 PM   #80
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Default Re: Proportioning valve delete

V8 Bob, Yes we agree the graph shows the effectiveness difference between the various designs - why do you suppose there is a difference - the reason is servo effect.

I'd like for you to describe the actual workings of what makes a servo brake a servo brake. I understand you description of what it LOOKS LIKE (2 shoes connected) but what I am getting at is what is actually happening to get us this "bonus" effect. My references clearly describe the servo effect being a result of the relationship of the shoe pivot point and the drum rotation direction causing the shoe to move towards the drum in one rotational direction, but AWAY from the drum in the opposite rotational direction. This can be applied to a shoe whether or not it is "connected" to another shoe or not.

I am NOT arguing the generic terms and references of certain design being "servo" and others not - what I am suggesting is that they do ALL benefit (to some degree) from Servo Action. Thew fact soem are called "non servo" may be well and good, but I still suggest it is quite misleading. Now granted in some cases - it (servo effect) is admittedly very little and in others a great deal. See graph above.

What I'd like you to describe is what mysterious feature do we gain by connecting the 2 shoes together - I see that as nothing more than making them "act" like a single shoe - just longer. Now teh ingenious part of anchoring them to a pin to allow them to work identically in both directions - yes that is what makes it so superior, but OTOH is a simple extension of a much simpler design and bound by similar features.
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Old 02-20-2010, 01:41 PM   #81
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Default Re: Proportioning valve delete

Bob, the popular adjustable Wildwood PV is described as adjusting pressures up to 60%, or some such number. Reading everything I could find on this valve, I got the distinct impression it operates at the set value throughout the pressure range, with no "knee" point. So I guess more to the point, do you know if it proportions by knee adjustment, pressure regulation after the knee pressure is reached, across the board or do the knee and percent regulation change in unision? Here is a case of the manufacturer knowing exactly what they have, but not making it clear to the buyer.

Your description of the problems with the hold off valve sure helped to expalin what happened to me on the interstate about 25 years ago. Heard brakes squealing and when the traffic finished parting, I was looking at a mid sized chevy sliding backwards into my lane and the guy holding on for dear life. Not a good sight.

Bill
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Old 02-20-2010, 07:50 PM   #82
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Default Re: Proportioning valve delete

B Blue, the old wilwood I bought 15 or 20 years ago had a graph that showed you the "Knee" point - it was THAT point which you were adjusting. Prior to that IIRC the relationship was 1:1.
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Old 02-21-2010, 08:38 AM   #83
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Default Re: Proportioning valve delete

Bill,
As HemiRambler stated, the "knee" or "crack" point is what is moved up and down in pressure when the knob is turned or adjusted on all of the adjustable PV’s I’ve used or come across. The slope, rate or percentage of pressure to the rear is fixed, as I stated earlier. Common low end adjustment usually starts around 200 PSI, and stops at about 1000 PSI. Please go back and review my post on prop valves.

HemiRambler,
I will try to "splain" the functions of servo and non-servo drum brakes again, as I know I might not be clear at times…I can even confuse myself J
Looking at the left front brake of a vehicle, let's start with a typical non-servo late model brake, with a double piston cylinder at the top, along with sliding anchors (allows the shoes to move up and down) at the top and bottom. When pressure is applied, the cylinder moves the forward facing or front shoe out against the drum, and the shoe tends to "wrap" into the drum because of the forward CC rotation, with the lower half of this shoe against it’s anchor, and providing the highest point of force, or retardation. The rear facing shoe is also pushed into the drum, but because of the CC drum rotation, tends to slide over the shoe with a lower percentage of braking or friction. With the vehicle going in reverse, the exact opposite will occur with the forces and movements on the shoes. Sliding upper/lower anchors, as opposed to fixed lower anchors, allow the shoes to move into the drum with higher forces, resulting in higher efficiency braking.

Now let's switch the LF brake to a common Duo-Servo design, with a double piston cylinder and single anchor at the top, and the shoes connected at the bottom with links and an adjuster (we'll leave out any self adjusting mechanisms at this time for simplicity). As pressure moves the front or Primary shoe out off it's anchor, CC drum rotation "wraps" the shoe, forcing it down and to the rear, but instead of being stopped by an anchor, it "SERVES" the rear or Secondary shoe THROUGH the adjuster, forcing the shoe out against the drum, AND UP into it's anchor, creating a "wedge" effect with the rear cylinder piston forces. The upper half of the secondary shoe is where the highest retard forces are. That's why the primary shoes usually have a shorter/thinner lining than the longer and sometimes thicker secondary shoes, and why you have to use care not to mix them when assembling a Duo- Servo brake. Going in reverse, all the forces and movements are also reversed, resulting in braking forces close to those going forward.

With a Uni-Servo brake, there is only one forward-facing piston, so the brake function and retardation are very close to the Duo-Servo, during forward braking only. When going in reverse, very little braking results, and that’s why this design was popular on surge-hitched trailers.
Bob
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Old 02-21-2010, 09:34 AM   #84
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Default Re: Proportioning valve delete

Bob, Thanks for that - I think we are "tripping" over terminology. For the sake of arguement & simplicity let's look at a single brake shoe. When rotated in one direction it is more effective than the other. What causes this?? I say it is the servo effect.
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Old 02-21-2010, 10:10 AM   #85
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Default Re: Proportioning valve delete

HemiRambler,
My definitions are based on info right out of my Bendix brake manuals, not generic or questionable reference material, and the many years of hands-on experience with brakes in general. A Servo drum brake is when one shoe serves the other, not the drum. Facts are facts.
Why a shoe is more or less effective depending on drum rotation is a fact, and is the result of the brake design and physics, both of which I am limited in knowledge to try and explain. It definitely isn't magic!

Bob
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Old 02-21-2010, 11:16 AM   #86
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Default Re: Proportioning valve delete

Bob, I think I understand your explanation pretty well. In fact, that as my understanding of how virtually all proportioning valves operated. Then I started to look for one to buy. This is typical of the descriptions I found:

WILWOOD PROPORITONING VALVES FEATURES:
Compact and lightweight forged billet aluminum construction has made Wilwood's proportioning valves the best available. Pressure adjustments range from 100-1000 PSI and provide for a maximum decrease of 57% in line pressure. This adjustment lets you fine tune the front to rear braking balance by proportionately decreasing the rear (or in some cases the front) brake line pressure. Can also be used to adjust individual front wheel braking in dirt track applications.

My problem is I cannot reconcile this description, especially the part about using it to adjust individual front wheel braking in dirt cars, with the concept of the Knee or cracking point.

Bill
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Old 02-21-2010, 01:23 PM   #87
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Default Re: Proportioning valve delete

Bill,
The crack point or knee is simply the point when the the pressure stops increasing normally, and starts to proportion less to the brakes plumbed to it.
Dirt track/roundy-round cars can use the PV to limit pressure to the left front since it's going to do the least amount of braking in the curves.
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Old 02-21-2010, 08:52 PM   #88
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Default Re: Proportioning valve delete

Bob I am not questioning Bendix - simply the terminology. Much like the difference between an ingition "coil" and a magneto "transformer" basically they are the same animal - terminology was changed because they do operate in different conditions with different parameters and don't work very well when intermixed.

Of course I realize there is no "magic" - I was simply trying to unravel the "mystery" attached to the term "servo effect" as related to drum brakes. You can question my reference material that is fine - I didn't write it. I used to work with a fella who worked for Bendix - maybe it's time to look him up again. He used to tell me all sorts of good stories about how Bendix would claim one thing - and the car manufacturers another - in the persuit of a sales edge.
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Old 02-22-2010, 08:20 AM   #89
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Default Re: Proportioning valve delete

HR,
My statement about questionable reference material was about mine, NOT yours. Several of my Bendix manuals illustrate and describe the physical layout of many of it's competitor’s drum brakes, using the terms "servo" and "non-servo". Do you really think Bendix would put into print "claims" about competing brakes in a service manual if they were not true?

You lost credibility when stating you may look up a fella, who worked at Bendix, who told you all sorts of stories... Just what the HELL does that have to do with this thread??? So now you are going to try and discredit the knowledge and experience I bring to the table, along with the very good and well known name of a company, from a “fella….with all sorts of good stories”. You obviously don't want to know what is fact, and I’ve obviously wasted a lot of my time. Hope you enjoy all the stories…
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Old 02-22-2010, 11:03 AM   #90
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Default Re: Proportioning valve delete

Bob No - you misunderstood my intentions - I am not now nor before arguing the terminology - I am certain I have misused several terms and is why I attached lengthy explanations in an effort to make the points understood inspite of the terminology. And no - the mention of looking up an old buddy was certainly NOT to discredit what you have posted - rather it was an attempt to understand why the apparent disparity in the terms. Do I think Bendix would (or you) would "make up" anything to prove a point - no certainly not. I was hoping my Transformer / Coil terminology example would have served to make that part clear. To answer your question about what it may have to do with this thread is simply this: Imagine, if you will, you are bendix- you just design a Huge Improvement to drum brakes design - one that will truely set yourself apart from the competition - you would be foolish to not try to differentiate yourself from the "lesser" competition as much as possible. Making the world BLACK and WHITE makes alot of Marketing sense. Their brakes suck because ours are better - ours are "DUO SERVO" theirs are not!!! Think about it -wasn't the term Self Energizing used prior to Servo?? Bendix couldn't very well lay claim to that (marketing wise) because the term was already in effect - no they had to market the improvement and come up with a term to describe the improvement. THAT term was Duo Servo - which simply meant that their new design was self energizing in BOTH directions. - Is THAT what really happened??? I dunno - that's what I GUESS happened - that's what I wanted to call and ask my buddy about - if THAT makes me loose credibility with you then there's not alot I can do about that.

I know where I work the marketing department is constantly trying to come up with new buzz words to differentiate us from our competition. I suspect Bendix and others did the same thing - I suspect in doing that - the waters have been muddied. The entire point of my posts was to try to get thru that mud (even though my poor use of terminology may have added to it) and see if we couldn't understand the function of brakes a little better. If my credibility is damaged for my effort - so be it.

Oh BTW - I looked thru several old references I had last night - the trend in the older was ones WAS to use the term Servo - as one shoe serving another. My new references described them differently - as I tried to recall and post earlier. YMMV
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Old 02-23-2010, 09:36 AM   #91
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Default Re: Proportioning valve delete

"Servo-action" is indeed the "twisting" of the brake shoes inside the drum, which increases the pressure on the shoes against the drum. "Non-servo" brakes don't have this twisting/force amplifying effect and require more pressure and are less effective. AMC used Bendix brakes and that's pretty much the description in the factory service manuals. The terms "Duo-Servo" and "Uni-Servo" are registered Bendix trademarks and why the Bendix manuals use them. AMC also used Wagner brakes for a few years -- Wagners on the American and Classic six cylinder cars, Bendix on the V-8 Classic and Ambassador. Wagner called their servo-action brakes "Compound Shoe", Bendix "Duo-Servo". Both are identical in operation. The Wagners have a different self-adjuster design with rods instead of a cable, but that's the only real difference in the design of them vs. the Bendix. Both work the same way.

The proportioning valve only limits maximum pressure to the rear wheels (or to a front wheel). Late 60s- early 70s AMCs used two different valves -- limited to 200 psi in the small cars (Javelin, AMX, American, Hornet) and 400 psi in the big ones (Classic, Rebel, Matador, Ambassador). Pressure is limited to that amount. Don't know what the GM combination valve pressures were, but they were used on later AMCs (mid 70s+). They are a fixed pressure also. The idea is to limit rear braking power so that the rear brakes don't lock up in a panic stop. I usually go out on a hard dirt road (plenty of those around where I live!) and slam on the brakes hard at about 45 mph. If the rears lock they are getting too much pressure. Adjust down and try again until they just start to lock. A wet parking lot will work too.

Speaking of servo/non-servo brakes, AMC used non-servo brakes instead of a proportioning valve in their first front disc brake cars to control rear brake "pressure". Bendix "Uni-Servo" brakes were used in the rear of all 65-67 AMCs with disc brakes (also Bendix -- four piston). Proportioning valves were used with 68-70 Bendix single piston discs. The GM style combination valve was used from 71 on. A combination valve has proportioning, brake light, and sometimes metering functions built into one junction block -- hence the name "combination valve". A metering valve, by the way, won't let ANY pressure to the FRONT brakes until ~100 psi is built up in the lines. It takes ~100 psi to overcome the springs in drum brakes. A metering valve makes sure all four brakes start to engage at the same time. It was used in many mid 70s cars for several years, then fell out of use by the late 70s. Someone figured out it really didn't make any difference if all four came on at the same time, you just can't have the rears locking up before the front or you could find your rear bumper catching up to and/or passing your front!
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Old 02-23-2010, 05:07 PM   #92
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Default Re: Proportioning valve delete

farna, What you described is a Pressure Limiting Valve - and yes it was used on some cars - it may have even been referred to as a "proportioning valve" as it performs a similar function. However it is not technically a Proportioning Valve it IS DIFFERENT.

In a Proportioning valve the "knee point" is where the pressure relationship changes from say 1 to 1 to then letting the rears only get a PERCENTAGE of the fronts. So the PRESSURE RISE in the REARS (after the "knee point") becomes a FRACTION of the pressure rise at the fronts. SO After the Changeover Pressure is reached the rear pressure does continue to rise - just not as fast as the fronts - hence the term "porportion"

The graph I was earlier thinking about was a Kelsey Hayes graph very much like the one pictured below. I got one with my Direct Connection Adjustable Proportioning valve (I bought 20 years ago) which I believe was actually manufactured by Kelsey Hayes. The ADJUSTMENT is varying the KNEE POINT (the pressure at which the portioning ratio change occurs) by twisting the knob you are changing the pressure - just not necessarily limiting it in a "flat line" sense - see pics.

Now whether or not the aftermarket offers Pressure Limiting valves as a common practice - I dunno - the only ones I ever bought were actual Proportioning Valves.

BTW - Notice the middle picture - that was for a Proportioning Valve with 5 preset adjustments. Depending on which adjustment you chose the pressure curve would follow along until the changeover pressure was reached and then decrease appropriately.

Last Pic (on right) shows the pressure relationship with a Pressure Limiting Valve as you described.

Quote:
Originally Posted by farna View Post

The proportioning valve only limits maximum pressure to the rear wheels (or to a front wheel). Late 60s- early 70s AMCs used two different valves -- limited to 200 psi in the small cars (Javelin, AMX, American, Hornet) and 400 psi in the big ones (Classic, Rebel, Matador, Ambassador). Pressure is limited to that amount. Don't know what the GM combination valve pressures were, but they were used on later AMCs (mid 70s+). They are a fixed pressure also. The idea is to limit rear braking power so that the rear brakes don't lock up in a panic stop. I usually go out on a hard dirt road (plenty of those around where I live!) and slam on the brakes hard at about 45 mph. If the rears lock they are getting too much pressure. Adjust down and try again until they just start to lock. A wet parking lot will work too.
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Old 02-23-2010, 05:48 PM   #93
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Default Re: Proportioning valve delete

Hmmm... well, I think I misunderstood the way the valve works. The "knee point" then is 200 psi and 400 psi on the AMC valves (which I believe were made by Bendix) is what you are saying, and from your explanation and the tech literature you provided, I'm sure I was mistaken and you are 100% correct. Makes more sense than just limiting overall pressure too.

The AMC tech manual says "Both the front and rear brakes receive full master cylinder pressure up to 200 psi. At higher pressures, the proportioning valve regulates the pressure to the rear wheel brake units." I was just reading it wrong. That is in the 1968 manual, later ones add the 400 psi for the larger cars.

Thanks for the correction!!
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Old 02-23-2010, 06:05 PM   #94
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Default Re: Proportioning valve delete

Good Christ, man! How many times does it need to be said?: DO NOT TAKE CHANCES ON BRAKES. Make them work before you get on the road. I do not recommend running without a prop valve. What has worked by chance for some may not work for you. Do not play games with a combination valve. Use an adjustable unit or leave the combo valve alone.
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Old 02-23-2010, 06:22 PM   #95
B Blue
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Default Re: Proportioning valve delete

Quote:
Originally Posted by re-animator View Post
Good Christ, man! How many times does it need to be said?: DO NOT TAKE CHANCES ON BRAKES. Make them work before you get on the road. I do not recommend running without a prop valve. What has worked by chance for some may not work for you. Do not play games with a combination valve. Use an adjustable unit or leave the combo valve alone.
I removed my proportioning valve because the rear brakes do not lock up before the fronts. Where do you recommend I place the proportioning valve? I favor the center console as the glove box tends to get a little messy, what with the registration and insurance papers.

Bill
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Old 02-24-2010, 03:09 PM   #96
farna
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Default Re: Proportioning valve delete

The valve can be mounted under the car in the rear or coming up through the trunk. Once it's set right you really don't need to touch it again. That's why a lot of rodders use the factory type non-adjustable combo valve right off the master cylinder. More on that below...

There's not a thing wrong with using a combination valve (factory proportioning valve) instead of an adjustable valve on most cars. I wouldn't use the factory type valve on anything real light like a 32, but get into the "fat fender" cars that weigh 2500 pounds or more and you're about the same weight as the cars the factory valves came in (Mustang, Camaro, and larger cars). For something that weighs less than 2500 pounds you may need a lower "knee point" to prevent the rears from locking up. See www.mpbrakes.com and read their technical pages. They have been recommending the GM combination valve for most street rods for years. Only something real light would need more.

I agree with you -- unless you have the same type brakes all the way around (four wheel drums or four wheel discs) you need some type of proportioning valve. With four wheel discs you may need them too, unless it's a factory type rear disc setup. They are usually designed not to need a proportioning valve. When both ends have balanced brakes of the same type a proportioning valve usually isn't necessary or used -- that's why the old drum/drum systems don't use one. The trick is that the rear drum size and wheel cylinder size are matched to work properly with the fronts though -- same with four wheel discs.

So what happens without a proportioning valve? In normal driving under normal (dry) conditions -- nothing. Brakes work fine. The problem is when conditions AREN'T normal -- mainly when the road is slippery (wet, snow, ice, loose gravel or sand on road, etc.). In normal driving you would usually be okay, you could feel or hear the rear brakes lock and given room and time react before anything bad happened. "Given room and time". In a panic situation -- some kid follows a ball in front of your car -- you don't have "room and time", and the rears lock and you slide. Sliding isn't stopping. Then there's the slippery conditions. You hit the brakes hard going down a wet/snowy/icy incline. You were going a little too fast (never!!), someone slammed on brakes in front of you, and suddenly your rear end wants to pas the front. Such situations are what the proportioning valve is really for. You can't control your driving conditions or other drivers. Many on this board are good enough drivers to react reasonably well to panic situations and control a car even if the rear brakes start to lock. But it's hard to stay off the brakes when you know if you press harder they will lock and make the situation worse when it looks like you're about to hit something and wreck your precious rod (we'll assume it's not your fault here).

I've been there on a motorcycle -- hit am unfamiliar blind curve a bit fast then discovered the curve got TIGHTER as I went around. You can't slow on a bike in a turn -- the bike wants to stand up and go straight if you do. You have to leave the throttle where it is or accelerate to pull around a curve, braking can kill you! But stepping on the brakes probably would have put me through the trees. So I forced myself to look around the curve where I needed to go (something else that's a must on a bike!) instead of the trees and side of the road I was afraid I might hit, and stayed on the throttle. Rode the white line on around it, but got around it! Then I slowed the f--- down, especially in curves I couldn't see good around!!
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