Proportioning Valves - Myth or Reality??

Ok guys - I shoulda been welding on my zoomies tonight, but instead saw this scrap Proportioning Valve and decided it needed to meet the bandsaw......


So here it is in all it's glory - the disrespected, often neglected and argueably the most misunderstood component on your car.... the Combination Valve!!! Appropriately named because it is a combination of the PROPORTIONING VALVE (upper left) - BRAKE LIGHT WARNING SWITCH (middle bottom - mostly missing in action but you get the picture) and lastly the METERING VALVE (far right). How it all works exactly??? Your guess is as good as mine, but I will try to explain what little (I think) I understand about it.


The PROPORTIONING VALVE is a simple piston backed with a spring. AS you depress your master cylinder EACH side (each bore) displaces the SAME amount of volume, (unless you have some exotic dual bore size getup - which for the sake of this we will assume you do not have but instead grabbed a typical GM, Ford, Chrysler, Amc master from the 60's or 70's) BUT!!! we need different pressures front/rear so to get that we put in this PISTON that can move proportionately under varying pressure - and viola - when it moves it REDUCES the pressure (to that side) since it has increased the volume in which the fluid is getting crammed into. And it's ALWAYS in the REAR BRAKES. WHY THE REARS? Because ideally you want maximum braking on the Front Wheels - why? Not only because they are MOST EFFECTIVE, but also because they are CRITICAL to safe handling. Consider HEAVY breaking entering a TURN....and your REAR TIRES Lock Up - now the rear of the car can pass you by as you SPIN OUT. That's the biggest problem with a REAR BIASED brake system. Ideally of course you want a PERFECT BALANCE Front/Rear but if you cannot (and likely won't under all conditions) you want the Fronts to lock First - barely.

BRAKE LIGHT WARNING SWITCH - simply the "V" notch cut into the center piston - a large imbalance in pressure shoves this "V" notch into an otherwise insulated stem - completing an electrical circuit and lighting your BRAKE LIGHT lettign you know you just blew a line (reason for the imbalance)

METERING VALVE - the valve that momentarily DELAYS the application of the FRONT BRAKES - Why? because applying the fronts is FIRST is a less stabil way to stop - just like applying your trailer brakes straightens out the whole rig-a-ma-role This becomes even more important when you combine DISCs up front with DRUMS in the rear - as we all know the drum shoes are retracted by their return springs and take a bit MORE fluid volume/pressure to contact the drums - "more" in relation to the super efficient discs up front anyways -AND under constant light braking you would entirely wear your fronts before the rears - so this helps balance that condition out as well.

RESIDUAL PRESSURE VALVE - I thought this was on the right side, but that makes no sense since that's for the front - possibly this was eleswhere in this particular brake system. Purpose: Mainly to keep pressure on the brake drum piston seals to prevent sucking air upon piston retraction. Not ALWAYS USED - LIP SPREADERS are another means to accomplish this same thing - drum brakes. Also used on DISC brakes to minimize the gap between the pads and rotors - reduce excessive pedal PRE-TRAVEL.


I don't mean to start any debate - I just wanted to try and shed a little light on this IMPORTANT yet often forgotten bit of FACTORY IRON. Think about how cheap the Factory's are - no grease fittings - plastic everywhere - nickle and dime-ing the cars to death. If they could sell them without these - "doo dads" surely they would if they could.

SO with all that said...I believe I am accurate on my descriptions here but FREELY ADMIT I AM NO EXPERT - should you KNOW I am wrong - PLEASE CORRECT ME!!!! Let's understand these components before we decide they are worthless.

 

Hmnnn....the other day I read on the Hamb that the FACTORY's NEVER installed proportioning valves and aftermarket ones were merely a restriction in the line - to which there were (at least one) who agreed this was correct. I naturally disagreed and it pretty much sorta died right there. It kinda bugged me that there's this apparent huge misconception about how these work and what the intended function really is.So I tried to put my money where my mouth is - in the notion that we might understand how these work. Am I just a bit too geeky to waste such time attempting to understand these things.

Oh well I tried. I'll shut up now.

 

After researching the combo valve and having a long
discussion with ElPolako I understand what each of the
components do.

I have one that looks very similar to that on my
Commander.

The tricky part is when you loose pressure enough to
activate the Idiot light, the pin locks the shuttle in place,
effectivley isolating the bad circuit.

You can simulate this if you are not careful when you bleed
your brakes. I found out the hard way.

I hope more people ask questions and understand. It's
not rocket science just hydraulics.

 

The way I understand it the proportionig valve also performs another important function in terms of proportioning related to the afforementioned blown brake line (wheel cylinder,caliper seal) ,and that is to redirect fluid to corners oppposite of each other so that the car will still stop (albeit not as well as it would with 4 corners) in a reasonably straight line in the event of one of the above mentioned failures.

Also what Hemi said about the bias to the fronts is something I can state is an absolutely immutable fact,as I have performed the asshole around appetite,emergency stop maneuver before .LOL Lucky for me as I maneuvered to the right the car spun down through the ditch instead of straight ahead into crash that was happening in front of me.

I went by the salvage on the way home and rounded up a proportioning valve and won't run without one in some form or another any more.

T.OUT

 

Thanks for the cutaway. BTW, you ever try to buy one of those? I haven't found a parts place that sells them, and I don't know if I trust one off of a junker. I did install an adjustable deal and inline residuals, but was not overly impressed... I can't lock 'em up. I may have an improper MC for my application (69 Mustang MC in a 50 Chev 350/350 w/M2). Anyway, thanks for the info. I want to go with a factory unit and ditch all my little inline pieces.

 

here is where it gets wacky...
although this particular metering valve has moving parts, some were in fact just like fuel logs--just a block with different sized holes drilled in them.

the most important fact to remember when dealing with brake hydraulics is NOTHING HAPPENS UNTIL ALL PRESSURES ARE EQUAL.

this can be facilitated by several methods,ranging from the often overlooked prop. valve (bendix couldn't have done a better job of splitting that thing,nice work), differing hose/line sizes, residual valves (that also help keep a certian AMOUNT of fluid in a caliper to avoid problems with sticking hardware)
and metering blocks.

this is why a good ol adjustable proportioning valve may be what is neccecary to "fine tune" your brake bias. even in a stock car!

back to the basics--nothing happens until all pressures are equal. this is what is responsible for 90 percent of all "brake pull" situations. lets say you have a hose that is developing a problem--one of the inner layers has seperated and the brake fluid has forced itself between them, effectively lessening the flow of fluid to one caliper/cylinder. the pressure BEFORE the obstruction equals out when the OTHER side applys force to the pads or shoes. the side with the mess gets less and presto! off you go into oncoming traffic.
this can also be accomplished with a leak. pressure applys evenly when you stomp the woah pedal. but as the leak bleeds off pressure, here comes the curb again.

when you change this bias from front to rear, you can see where switching ends or nose diving would occur.

 

FWIW, my 52 Chevy uses the Mustang master cyl. plumbed straight to the calipers/wheel cylinders, (no power brakes, no prop. vavle, no external RPVs, no metering valve) and it works real good. (But then I've never been accused of having skinny legs...). Worked fine when it was under the floor, and works even better now that it's on the firewall. I wouldn't say this is the best combo for every car, but it works real good on mine.

Thanks for the words & pic, HemiRambler. Good post!

 

So what we're calling a non-adjustable Proportioning valve is really nothing more than a preset, spring loaded ACCUMULATOR? (I'm talking JUST the Pro-valve here...not the complete Combo-valve assembly its a part of.)
An adjustable one having the ability to set the spring pressure inside the accumulator to vary the point at which the piston moves.
Looks like some minor adjustability could be worked into the NON-adjustable one simply by adding shims or shaving the threaded end plug...depending what you need.

That angled port from the spring side of the Pro-valve piston?
Just a drainback of some kind to prevent fluid thats leaked past the piston from stopping the piston movement if it were to build up...or does it have some use in increasing piston resistance?
I doubt an aftermarket one has that drainback...or whatever it is.

Can't believe I've never pulled one of those things apart before...

 

Why would you want your brakes to lock up? If they lock up, there aren't doing their job. Basicly your skiding, not stopping.

 

Some time back one of the aftermarket brake guys was interviewed by a magazine.

One thing I took away from the article was that they weren't recommending a proportioning valve on a car with disproportionately sized bigs and littles.
The theory being - and it seems right - the larger diameter rear wheel has more leverage and needs more pressure instead of less.

That holds true in my 32 with 68-90 Mustang discs up front and 68 Merc wagon drum brakes in the rear.
The 32 does have a propo valve and it's backed all the way off.
Tire diameters are 24" front and 30 1/2" rear.

I do agree that a metering valve would be a good addition to this car though.
It stops quite well and handling is ok and a couple of highway stomp on the brakes deals the car remained straight.

Even so, I think a metering valve should be in there.
(One of the aftermarket hot rod brake outfits sells one.
$70. last time I looked, but you ought to be able to get the same one at a parts store with a discount.
For the 31, a metering valve goes in right up front, but I'm skipping the propo valve to start with.
There will be a mounting area and the lines will be plumbed for an easy installation if it turns out a propo valve is required.
Brakes on the 31 are Camaro disc in front - 10 1/2" rotors compared to the Mustangs 11" rotors.
Since the donor car weights are similar I expect similar braking in both cars far as the front discs go.
Rear drums on the 31 are Ford, same size as the Merc drums on the 32.

Tire diameters on the 31 are 25" front and 28" rear, so it's possible a propo valve may be required.
Gonna drive it first and see what's up.

 

If you can lock up your brakes that proves they are sufficiently powerful for the car they're on.
Brake fade notwithstanding.

It's the drivers job to modulate brake pressures on cars lacking the modern anti-lockup feature.

 

I'm not seeing something right...
Wouldn't that ADD proportioning to the mix? I was figuring that you would keep normal actuation by screwing the knob IN tight till the piston shaft bottomed thru the spring...thus the valve would be inoperative and act as though no accumulator valve were in use.

Never used one or even had one in my hands before, so I'm just trying to learn something about how they work here...not say anyone is wrong!!!

Maybe my visualization is all wrong...

I wonder if theres a cutaway of an aftermarket adjustable one on the NET somewhere. I did a quick search but came up bust.

 

Precisely!

 

Here is the short story. First of all, don't confuse propo valve with switch body that is merely a switch to turn on idiot light for unbalanced pressure, due to problem in the system.

1. With a single master cylinder and 4-point drums, propo valve is not necessary because you can accomodate any unbalance by adjusting. If the front brakes lock up and rears don't quite engage enough, simply back of the adjustment a bit on the fronts.

2. With a mix-matched system, like on a hot rod where you want juice but with a single master and mixing wheel cylinders, with disc on front and drum on rear, if you don't use propo valve the discs will lock up and the drums will barely engage. That can be helped without using a propo valve by introducing air in the lines in front to soften the applicantion or adjusting the rears up real close, but then the drums will run hot all the time. Propo valve is better choice.

2. With a dual master cylinder made for 4-point drums, propo valve not needed, if the wheel cylinders all match.

3. With a dual master cylinder made for discs on front and drums on back, the propo-function is built into the master cylinder.

It's all got to do with volume (proportion thereof), relative to the master cylinder bore size and the wheel cylinder bore size. With a disc, the running clearance is so small that it takes very minimal application to engage, while it takes more to move the mechanism on a drum setup.

Any disagreement with my analysis is okay, because this is all just knowledge I have picked up along the way from first hand experience, not having gotten it from any book. If you don't understand the entire subject feel free to read the books and come up with your own opinion, not based on actual hands on experience. I just picked this information up along the way, having worked on brakes before they even used a pedal, but only had a hand brake, then when they got a pedal but the primary brake was still a handle and they called the foot brake the auxaillary brake, and then when they called the foot brake a foot brake and the hand brake a emergency brake. **(see footnote)
Then; low-and-behold they took off the pull-rods and put in liquid lines when they invented juice brakes! After that................... yata-yata-yata-..............

**footnote; At that time in history people knew how to adjust them (the mechanical brakes), where they would squawk the tires (lay down black marks)on pavement, then they got too lazy and the brakes failed from lack of attention, then several decades later people started the myth (bull shit) that hydraulic was safer, simply because no body knew how to maintain and adjust them anymore; coupled with the fact that maintaining and adjusting mechanicals did take time (up to a half-day in the shop) Maintenance on juice brakes was merely an adjustment every 3,000 miles and replacement of the master cylinder (preventive maintenance) every 20,000 miles-------

 

Heh heh! Me too! I don't mind applying a little muscle, but lemmie ask you something then... do you feel like the rear brakes are doing most of the work? My discs don't feel like they are grabbing all that much. I couldn't have them plumbed backwards could I? I was under the impression that the larger resivoir (front one) was for the Disc brakes. At first I thought that I needed to put the adjustable prop valve in to back off the rear brakes, but that didn't do much.

Just wondering.

 

Backed off was perhaps a poor choice of words.
I don't remember which way I spun the adjuster knob for sure.
I did the adjustments after doing the back country road brake testing and the way the propo ended up is the same as not having one in the system.

Clear?
Or did I just muddy the waters some more....

Now that I think about it, there's the propo for the 31 if it needs one....

 

Take a look here:

http://www.stangerssite.com/brakevalve.html
Shows an exploded view of a factory installed Mustang adjustable propo valve.

 

Didn't you borrow that valve from me?

 

Did you want that back ?? I'll see if I still have all the pieces.........I've got some glue here somewhere............actually Stan donated it.

 

Yo Baby, I do NOT claim to understand how ALL combination valves work. The "diagonally split" braking systems are foreign to me other than understanding the basic concept. Just to clarify - the proportioning valves as used in the 60's 70's on the BIG THREE where they are split Front to Rear do not redirect any fluid. They serve only to REDUCE PRESSURE to the rear brakes to prevent REAR BIAS (prevent the rears from locking up first) - If you look at the valve here you can see the rear line exits (far left) as a single fitting - which is later split into left/right circuits. You can also see that the front RIGHT and LEFT lines share a common reservior within the combination valve - thus not allowing any LEFT/RIGHT adjustments. In the ONE I show above the system is split (isolated) FRONT to REAR only.

Also mentioned by others is the statement that you can use these "proportioning valves" to SEAL a leak from one half from the other - as would be desireable if you were to use this on a SINGLE master cylinder (isolating Fronts from Rears). While SOME COMBINATION VALVES work this way - NOT ALL DO!! If you look close at the RIGHT side of this one you will see the shuttle does not close off the FRONT INPUT from the FRONT OUTPUTS. So THIS particular Combination would not be a great choice for an UPGRADE to a single master system.

 

Stickylifter, Yes I have bought these - normally I try to get a FACTORY one (NEW) that comes from a vehicle that is SUPER CLOSE to my own - curb weight, brake size/type, CG. For instance I just added 11-1/2" discs to the front of my '47 truck and plan on updating the rears drums as well. I went with a 70's Ford Truck Combination Valve - same front rotors - same rear drums - similar weight - similar CG. Made sense as a good starting point to me. Of course buying one from the DEALER is expensize!!!! You might try http://www.mbmbrakeboosters.com/proportioning_valves.html Their website says they sell to dealers only - but you can contact them and ask who their nearest dealer to you is. I also see them sold NEW on Ebay all the time - but I suppose you had really better know which one you need - matching them to your requirements is very important.

However - not being able to lock them up suggests a problem - you may have mismatched components that prevents you from attaining enough line pressure. Aside from not being able to lock them up - how does it stop??? Not suggesting it is ok because I think that having enough pedal leverage matched with the appropriate diameter master is gonna be key to allowing you to function correctly.

Time to evaluate your system. Adding in a different proportioning valve now isn't gonna increase your FRONT pressure - unless something's broke. Remember the combination valve doesn't REDUCE the pressure to the FRONTS - just the rears. You want max pressure to the fronts - well you want to be ABLE to get max pressure to the fronts - hopefully you won't need THAT all the time!!!

 

LUX BLUE - I don't doubt you - but I'd love to see one - got any pics??? Have saw - will travel.

I think I get what you are saying here, but your words are slightly misleading. Front to Rear pressure is NOT always equal - FRONT LINE PRESSURE might be 1,500 PSI while the REAR only 500 PSI - this is a result and function of the Proportioning Valve. I think we are agreeing????

Yabbut - this is another area of varying opinions. A stock car is not likely gonna be IMPROVED by the addition of a Adjustable Proportioning Valve - simply because the FACTORY is damn good at making these right in the first place. Now IF you have CHANGED things - tires, brakes, CG height etc etc - basically all the things we hot rodders do - then YES we have UPSET the balance designed in and we could benefit from REMOVING the factory Proportioning valve and REPLACING IT with an adjustable one.

Yep I agree - had this happen TWICE this year on two separate cars - brake hose (appeared perfect) had collapsed internally and pinched off any fluid from passing - hit the brakes and instant lane changer if you weren't careful. Funny thing was HOW FAST this happened - I had bled the brakes a week earlier!!!! After noticing this I couldn't bleed one side.

Can't say my leaks were ever small enough to let that happen - my pedal usually just dropped 1/2 way to the floor and my attention was FULL BORE, but I could see what you describe happening - my luck just doesn't run that way much.

I think I follow you here....but to restate REAR BIASED brakes is a BAD thing - and hopefully we all avoid that.......also NOSE DIVING shouldn't be a huge consideration as weight transfer is gonna make that a reality no matter what. I think we are in agreement here as well. There are TONS of factors that can change your bias from front to rear or vice versa - sticky pads - different size tires - different tire compounds - the list is huge - the trick is to be able to adjust for these so that you can keep your system in tip top condition.

 

C9, This big/little tire thing has a certain logic that's tough to argue with - I suppose the CHALLENGE would be to determine whether or not you fall into this category. If your rears never lock up - I suppose that's a clue your FRONT BIASED way too much. Keep in mind there are other ways to shift your bias from front to rear and vice versa.

Ahmmm....I don't think you can draw this conclusion just yet. Actually if you delve further into a Proportioning valve you will see they are designed such that they actually CHANGE thier rate from basically NOT being there (initially) to then proportionately reducing your rear line pressure. Changing the adjustment CHANGES the POINT of pressure in which this relationship occurs. The RATE of proportioning is determined by the spring - the point at which it enters the equation is determined by the preload in the spring. So while you might have removed all the external preload - the spring was still there and still able to function - meaning you didn't defeat it by adjusting it - you merely changed the pressure where it activated.

yeah I agree - this is one of those commonly left off parts - guys try them without and see no difference and determine they were useless. Unfortunately without a skidpad and the millions of dollars that GM has we necessarily aren't qualified to determine they have no effect as the seat of our pants isn't always the most accurate means of measurement. Not that we should ignore it

I agree - what could it hurt???

 

the metering valves that are no mor that blocks with holes drilled on them are primarily used on newer foreign cars ( I think that is why they will not shoot fluid out of the master when you mash the pedal with the cap off,too...)

on the pressures, we are in definite agreement. what I was trying to get across is if you are operating one,two or thirty hydraulic assemblies, they wont move at all (or at least not properly)until the pressures are equal across the board. metering is what is neccecary to avoid blowing out said hydraulics, or to limit travel via volume

as far as the adjustable prop valve goes, I have seen them used to help"flatten out" newer trucks. yes the factory does a bang up job, but how many body styles have been changed on the same chassis? some add mass, some take it away. think about a 67 2 door hardtop versus a 67 wagon...same chassis, and more often than not, same brakes!

I like you Hemi, you're alright. this beats the snot outta talkin' about what color of flat black is the flattest

 

As far as I can see the proportioning valve is nothing more than a speed control. Preaaure is the same but it can be delayed from one end of the vehicle to the other by the prop valve. So if you have too much rear brake put in the valve and adjust it so the fronts come in first and it balances out the system for better braking. Ive looked at the wilwood and speedway stuff and speedway sells one that looks just like some of the shit ive used in hydraulic applications. They also use them in air applications and they work the same the pressure never changes but the time frame that you make full pressure does with adjustments. As far as metering valves im gonna be honest I got no clue and have never used one. I put residual valves im my last two cars and really ive never seen a difference. All my cars had the M/C mounted under the floor and lines to the brakes and no bull shit in between and they all worked. Call me lucky I guess. I put residual valves im my 32 then plumbed up a 30 a with disc drum and one of them new dual sided outlet M/C's with no extras and I like the brakes and the feel better than my 32. My 32 has way more front than rear so if i was gonna do anything id put the prop valve in the front .
Dave
ps: im no expert either.

 

Prop valves don't work very well and actually limit rear braking even to the point of rendering them usless, adjustables aren't much better because they limit the pressure availble to the brakes. The front and rear brakes should wear out at the same rate if your getting good braking, if the front wear faster your prop valve isn't working correctly. It may be working as far as the MFG is concerned but it is not effective in the application of brake force.

If prop valves worked they would not have tried ABS and traction control. If you want a valve that that will allow the front to lock up before the rear in a panic stop and still apply full brake pressure to the rear you need a different valve. The only one I know of is a lock resistant brake valve from DPI Racing Products. It is particularly good with fat tires on the rear and discs on all four.

 

if that were the case, then why is there a prop valve before or after the abs module on 90 percent of the abs vehicles out there? the object of anti lock brakes is clearly to NOT LOCK UP THE BRAKES! front or rear reguardless, as soon as the wheel stops spinning, all brake power is lost! this is why it feels like you"speed up" when your brakes lock up on ice --YOU DO! The weight bias of the car (nosedive) goes away and presto, all you have is a large mass doing what it does best when sliding--speeding up! (then,typically stopping when it finds another immovable object to crash into.)

 

First off, my thanks to HemiRambler for throwing this out here for
discussion. I've driven/ridden in many rods and racers with dismal brakes.
My experience with the combo valves(GM variety) has noted this, OE valves
are cast iron while their service replacements are brass. Just a thought
before anyone goes junkyard trippin for em. Even so without available
adjustment I figure their just a shot in the dark. Great thead,Thanks.

 

Some pickups and vans have a brake valve on the rear frame to prevent brake lockup when unloaded.
Its attached by an arm to the rear axle to sense how far the springs have compressed due to the weight being carried.

Is that a prop valve and could it be used in place of an aftermarket adjustable valve? Adjustment of brake pressure could be made by using an adjustable link to the rear axle...maybe?