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Proportioning valve delete

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

  1. panic
    Joined: Jan 3, 2004
    Posts: 1,450

    panic

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

    Duh!
     
  2. HemiRambler
    Joined: Aug 26, 2005
    Posts: 4,208

    HemiRambler
    Member

    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.
     
  3. Hnstray
    Joined: Aug 23, 2009
    Posts: 12,355

    Hnstray
    ALLIANCE MEMBER
    from Quincy, IL

    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
     
    Last edited: Feb 11, 2010
  4. THE SPEED ADDICT
    Joined: Mar 31, 2007
    Posts: 355

    THE SPEED ADDICT
    Member

     
  5. ehdubya
    Joined: Aug 27, 2008
    Posts: 2,315

    ehdubya
    Member

    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.
     
  6. Drive Em
    Joined: Aug 25, 2006
    Posts: 1,748

    Drive Em
    Member

    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?
     
  7. 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.
     
  8. ehdubya
    Joined: Aug 27, 2008
    Posts: 2,315

    ehdubya
    Member

    Fronts can stand more pressure regardless of the type of brake

    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...

    plenty of good info here... http://www.stoptech.com/tech_info/tech_white_papers.shtml
     
    Last edited: Feb 12, 2010
  9. Stefan T
    Joined: Sep 15, 2008
    Posts: 2,165

    Stefan T
    Member
    from Sweden

    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
     
  10. B Blue
    Joined: Jul 30, 2009
    Posts: 281

    B Blue
    Member

    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
     
  11. claymore
    Joined: Feb 21, 2009
    Posts: 896

    claymore
    BANNED


    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.
     
  12. Truckedup
    Joined: Jul 25, 2006
    Posts: 4,661

    Truckedup
    Member

    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.
     
  13. Essex_29
    Joined: Dec 27, 2007
    Posts: 145

    Essex_29
    Member
    from Finland

    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?:rolleyes:

    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.
     
  14. HemiRambler
    Joined: Aug 26, 2005
    Posts: 4,208

    HemiRambler
    Member

    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

     
  15. B Blue
    Joined: Jul 30, 2009
    Posts: 281

    B Blue
    Member

    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
     
  16. HemiRambler
    Joined: Aug 26, 2005
    Posts: 4,208

    HemiRambler
    Member

    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.

     
  17. B Blue
    Joined: Jul 30, 2009
    Posts: 281

    B Blue
    Member

    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
     
  18. HemiRambler
    Joined: Aug 26, 2005
    Posts: 4,208

    HemiRambler
    Member

    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.
     

    Attached Files:

  19. 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.
     
  20. ago
    Joined: Oct 12, 2005
    Posts: 2,199

    ago
    Member
    from pgh. pa.

    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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  21. henryj429
    Joined: Jan 18, 2007
    Posts: 1,063

    henryj429
    Member

    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?
     
  22. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,966

    V8 Bob
    ALLIANCE MEMBER

    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&#8217;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: Feb 13, 2010
  23. HemiRambler
    Joined: Aug 26, 2005
    Posts: 4,208

    HemiRambler
    Member

    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.

     
  24. HemiRambler
    Joined: Aug 26, 2005
    Posts: 4,208

    HemiRambler
    Member

    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.

     
  25. ehdubya
    Joined: Aug 27, 2008
    Posts: 2,315

    ehdubya
    Member

    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 [​IMG]

    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: Feb 13, 2010
  26. B Blue
    Joined: Jul 30, 2009
    Posts: 281

    B Blue
    Member

    "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
     
  27. ehdubya
    Joined: Aug 27, 2008
    Posts: 2,315

    ehdubya
    Member

    thanks, I found this explanation
     
  28. 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.
     
  29. HemiRambler
    Joined: Aug 26, 2005
    Posts: 4,208

    HemiRambler
    Member

    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.

     
  30. Essex_29
    Joined: Dec 27, 2007
    Posts: 145

    Essex_29
    Member
    from Finland

    Since the original question in this thread reamins unanswered, I'll answer it myself.:rolleyes:
    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.

    [​IMG]

    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:D
     

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