Register now to get rid of these ads!
  1. Hey fellas, just in case you missed it - The Rodder's Journal and The Jalopy Journal is celebrating 20 years of bringing you traditional hot rods and customs by offering you a one-year subscription to TRJ and a H.A.M.B. Alliance membership for only $75. Click here for details.

Proportioning valve delete

Discussion in 'The Hokey Ass Message Board' started by Essex_29, Feb 10, 2010.

  1. Essex_29
    Joined:
    Dec 27, 2007
    Posts:
    35
    Location:
    Finland

    Essex_29 Member

    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?:confused:
  2. V8 Bob
    Joined:
    Feb 6, 2007
    Posts:
    1,369
    Location:
    Granger (Northern) Indiana

    V8 Bob
    ALLIANCE MEMBER

    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
  3. HemiRambler
    Joined:
    Aug 26, 2005
    Posts:
    3,958
    Location:
    Cleveland, Ohio

    HemiRambler Member

    V8 Bob beat me to the punch! An adjustable proportioning valve is better than none at all.
  4. Swifster
    Joined:
    Dec 16, 2006
    Posts:
    1,451
    Location:
    Lakeland, FL

    Swifster Member

    X3 - New adjustable valve
    Register now to get rid of these ads!

  5. B Blue
    Joined:
    Jul 30, 2009
    Posts:
    281
    Location:
    Connersville

    B Blue Member

    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
  6. bulletproof1
    Joined:
    Feb 23, 2004
    Posts:
    2,067
    Location:
    tulsa okla

    bulletproof1 Member

    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......
  7. Hnstray
    Joined:
    Aug 23, 2009
    Posts:
    5,185
    Location:
    Quincy, IL

    Hnstray
    ALLIANCE MEMBER

    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
  8. 1934coupe
    Joined:
    Feb 22, 2007
    Posts:
    1,290
    Location:
    Hudson Valley NY

    1934coupe Member

    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
  9. Home Brew
    Joined:
    Oct 12, 2007
    Posts:
    86
    Location:
    hannibal, mo.

    Home Brew Member

    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.
  10. rustynewyorker
    Joined:
    Sep 26, 2004
    Posts:
    15,807
    Location:
    Upstate New York, watching my New Yorker Rust

    rustynewyorker Member

    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.
  11. Hnstray
    Joined:
    Aug 23, 2009
    Posts:
    5,185
    Location:
    Quincy, IL

    Hnstray
    ALLIANCE MEMBER

    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
  12. Just Jones
    Joined:
    Jan 11, 2005
    Posts:
    920
    Location:
    Southern Oregon

    Just Jones Member

    x 2

    I have a very similar set up on my '40 pickup, and no prop valve. Seems to work just fine.
  13. HemiRambler
    Joined:
    Aug 26, 2005
    Posts:
    3,958
    Location:
    Cleveland, Ohio

    HemiRambler Member

    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
  14. chop32
    Joined:
    Oct 13, 2002
    Posts:
    1,073
    Location:
    Vallejo, CA

    chop32
    ALLIANCE MEMBER

    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?
  15. 345 DeSoto
    Joined:
    Jul 15, 2008
    Posts:
    2,156
    Location:
    Summer Skaneateles,NY/Winter Port St.Lucie, FL

    345 DeSoto Member

    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...
  16. Hnstray
    Joined:
    Aug 23, 2009
    Posts:
    5,185
    Location:
    Quincy, IL

    Hnstray
    ALLIANCE MEMBER


    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
  17. JAKE'S-Pumpkinella54
    Joined:
    Oct 3, 2009
    Posts:
    1,726
    Location:
    in a place where everyone knows your name ...

    JAKE'S-Pumpkinella54 Member

    how good are you at steering doing 65 with no brakes
  18. Ian Berky
    Joined:
    Nov 28, 2007
    Posts:
    3,643
    Location:
    Riverside, California

    Ian Berky Member

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

    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!!:eek:
  19. Drive Em
    Joined:
    Aug 25, 2006
    Posts:
    1,738
    Location:
    socorro.Tx.

    Drive Em Member

    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.
  20. Ebbsspeed
    Joined:
    Nov 11, 2005
    Posts:
    3,025
    Location:
    Shawnee, KS 66218

    Ebbsspeed
    ALLIANCE MEMBER

    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.
  21. johnboy13
    Joined:
    May 1, 2007
    Posts:
    1,075
    Location:
    Rockford, Il

    johnboy13 Member

    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.
  22. Groucho
    Joined:
    Dec 22, 2002
    Posts:
    11,464
    Location:
    300 feet West of Burbank Airport

    Groucho Member

    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.
  23. chop32
    Joined:
    Oct 13, 2002
    Posts:
    1,073
    Location:
    Vallejo, CA

    chop32
    ALLIANCE MEMBER

    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.

    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!
  24. panic
    Joined:
    Jan 3, 2004
    Posts:
    1,456

    panic BANNED

    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.
  25. B Blue
    Joined:
    Jul 30, 2009
    Posts:
    281
    Location:
    Connersville

    B Blue Member

    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
  26. Essex_29
    Joined:
    Dec 27, 2007
    Posts:
    35
    Location:
    Finland

    Essex_29 Member

    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 :rolleyes:
    "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.
  27. Hnstray
    Joined:
    Aug 23, 2009
    Posts:
    5,185
    Location:
    Quincy, IL

    Hnstray
    ALLIANCE MEMBER


    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
  28. dwcustom
    Joined:
    May 31, 2009
    Posts:
    83
    Location:
    Vero Beach Fl

    dwcustom Member

    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!
  29. gasserlouie
    Joined:
    Oct 15, 2006
    Posts:
    1,392
    Location:
    Lincoln, Nebraska or a swap meet somewhere

    gasserlouie Member

    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.

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2013 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.