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Toss the prop valve?

Discussion in 'The Garage' started by garlicbreath, Dec 17, 2006.

  1. garlicbreath

    garlicbreath 1/2 ton status

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    Has anyone just tossed their prop valve and used an adjustable valve like the drag racers use?

    My brakes suck.

    I put one tons in and a one ton master. I haven't done the booster yet because the the problem seems to be more in the fluid system than the assist.

    I have bled, bled, gravity bled, replaced the master, and the pedal is still soft and moves way to much before the brakes grab.

    Another reason I am questioning the prop valve is the reset button on the end pulses when I push the pedal, and leaks from the same spot.

    SO, can I axe that sucker and put the wilwood one in the rear brake line?
     
  2. beater_k20

    beater_k20 Banned

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    it shouldnt leak at all.

    that's where your low pedal is coming from. its drawing air into the system.
     
  3. 79k20350

    79k20350 3/4 ton status

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    The proportoining valve on our trucks are also distibution blocks. Take out the sytem that distributes power in the stocker and get a willwood inline one.
     
  4. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    I ditched mine, however, mine is a dedicated trail rig. I didn't put any thing into replace it. New lines from the master all the way to the wheels. Not sure if you'd want to do that on something road driven.
     
  5. blazd88

    blazd88 1/2 ton status

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    Im having similar problems with mine. New MC and still no rear pressure. Going to try and reset the prop and go from there. Let me know how it goes.
     
  6. makovai

    makovai 1/2 ton status

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    me 3,
    I just converted mine to 4 wheel disc, and have now replaced everything except the prop valve. (new calipers, m/c, booster) My system deosn't leak anywhere, and i have blead the $h1t out of it, yet i still have spongy brakes, that cannot stop the truck.
     
  7. fattymctrickle

    fattymctrickle Newbie

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    Have any of you ever tried a hydro-assist out of a diesel or 3/4 ton suburban? I heard they have a way higher assist pressure.
     
  8. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    Hydro boost brakes are generally considered better. It is difficult sometimes to get all the air bled out and if you are having trouble I strongly recommend a power bleeder.
     
  9. makovai

    makovai 1/2 ton status

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    i have a hydra boost already pulled and paid for from a 78 3/4 ton sitting in my garage. I'm not sure why i cant seem to pull the trigger and just convert, but somthing is telling me not to. I would still need a different p/s pump as i forgot to grab that off the rig.
    something about 1 unit controlling my brakes and steering concerns me i geuss.
     
  10. ntsqd

    ntsqd 1/2 ton status

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    Something an SCBD thread with Triaged brought to light are "Quick Take-up" m/c's.
    I'm not sure of the year GM started doing this, but my '91 1/2t Sub has this. The two different parts are the m/c and the calipers. The m/c difference is obvious as these are the m/c's with the stepped bores. The difference in the calipers is essentially undetectable by eye.

    If you have quick take-up calipers and a non qwik take-up m/c you will likely never get a high pedal. Everything could be perfect and b/c of this small machining difference in the calipers, the system will have a low pedal.
    The pistons in these calipers are retracted further to reduce drag (CAFE MPG's), so it will require more pedal travel to move the pads to the rotors.
     
  11. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    If that is the case with some of these peoples' problems then a residual valve should cure that. Residual valves come in 4 and 10 pound valves.
     
  12. garlicbreath

    garlicbreath 1/2 ton status

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    My calipers are stock 78 one ton and the master is listed for the same truck, they are just on a half ton blazer.
     
  13. badger red

    badger red 1/2 ton status

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    Which residual valve would you use for disc brakes?
     
  14. blazinzuk

    blazinzuk Buzzbox voodoo Premium Member GMOTM Winner

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    If you are leaking fluid anywhere it may draw air into the system hence your bad brakes. I am running stock one ton brakes on a stock half ton master and booster and it works fine. I had to bleed my brakes alot to get all the air out of them. Mabey 15 times or so. I had let my whole system go dry though.
     
  15. garlicbreath

    garlicbreath 1/2 ton status

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    So if I am thinking right, the prop valve lowers pressure or volume to the rear brakes only, acts as a pass through for the front, and as a friend discribed it today, has a safety valve that senses low pressure and blocks off that circuit so the other half of the system still works?

    If I remove it, I will seperate the 2 circuit anyways, and the adjustable valve would limit pressure-flow to the rear brakes right?
     
  16. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    That would be correct with the exception that the prop valve still allows for separate brakes front and rear but does have the switch for low pressure to turn your brake light on if there's a problem.
     
  17. MuddinManny

    MuddinManny Banned

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    Makovai,

    How are you bleeding your system? I have a Motive Power Brake Bleeder and it's the bosnizzle! :bow: A gallon or two of brake fluid, pressure at the MC, and starting with the drivers side rear, passenger rear, passenger front, drivers front, in about 30 minutes, with all the old fluid and air out, new juice in, you should be solid as a rock! What gives mah man?

    Manny
     
  18. ntsqd

    ntsqd 1/2 ton status

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    They might and they might not.
    If you go with the common disc brake application RPV (normally 2 lbs) then you haven't changed anything except made your wallet lighter. The way those calipers work is they allow the piston seal to distort further (b4 limiting out & allowing the piston to slide thru it, which is pad wear compensation, not normal single apply useage).
    The force retracting the pads has increased, due to the increased seal distortion, beyond the value of the RPV. So the pistons will return to the point where pressure is reduced to the point where the RPV closes, no matter where the RPV is located in the system. To reduce the retraction distance in this manner means that the RPV needs to be a higher pressure.

    If you used a 10 lbs RPV then you run the possible risk of the pads excessively dragging and it may or may not fix the retraction problem. It could fix the retration problem and cause dragging pads, or it could fix it and not cause the pads to drag. I've not done this, nor know of anyone who has, so it's a guess at best. Some people don't seem to have a problem w/ 10lbs RPV's in a normal disc circuit, others do.

    The correct fix would be to either dump the High Retraction calipers in favor of the earlier calipers, or go to the High Retraction application m/c. Personally I'd go with replacing the calipers.
     

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