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Searched again--cant figure it out! Proportioning valve? MC? Help!

Discussion in 'The Garage' started by K5thatShmobs, Nov 25, 2002.

  1. K5thatShmobs

    K5thatShmobs 1/2 ton status

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    When bleeding the brakes I'm getting very poor pressure to the rear brakeline... the fronts have more, but when bleeding the rears, fluid barely dribbles out. Pedal pressure feels firm when the engines off, but as soon as you start it, the pedal gets firm only an inch or two from the floor. Could this be the proportioning valve? Master cylinder? I have to get this truck done by this wednesday! Thanks all...
     
  2. BigOrange90Jimmy

    BigOrange90Jimmy 1/2 ton status Premium Member

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    did you check that little filter on the vaccuum line from the engine? i replaced my MC because i couldn't get any pressure only to find out that's what the problem is. also remember to start with the brake the furtherest away from the MC.
     
  3. zakk

    zakk 1/2 ton status

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    Just replace the MC, bleed it REALLY well, if the MC is good, it will be easier to find the problem.

    I had NO rear brakes and the M/C was the culprit. now i stop like a sports car /forums/images/graemlins/cool.gif
     
  4. MJF

    MJF 1/2 ton status

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    I'm still in the same boat as you. I replaced the MC & prop valve. I went throught he bleeding process in the correct order with good pedal. As soon as I start it, all the way to the floor. I'm pissed.

    I'm about to put a for sale sign on it, sign the title, & put the keys in it.
     
  5. zakk

    zakk 1/2 ton status

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    booster bad?
     
  6. MJF

    MJF 1/2 ton status

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    I've tried two different boosters. Neither were new, but both worked when the truck was parked. I'm lost.

    Sorry to hijack your thread, but we seem to have the same problem.
     
  7. BigOrange90Jimmy

    BigOrange90Jimmy 1/2 ton status Premium Member

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    i stand by my filter theory /forums/images/graemlins/rotfl.gif i couldn't figure it out either. i finally took that thing off and tried to blow through it and it felt like i had my lips shut. i robbed one off my parts k5 and tried it and it worked like a champ.
     
  8. slider

    slider 1/2 ton status

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    Your rear brakes flow way less fluid than the fronts. Have you cleaned out the bleeders, they get alot of rust and crap in them and will not let much fluid out when bleeding. Pull them out and run a small drill bit thru the hole and the nipple area. Then blow the crap out of them and I bet it will bleed correctly. If not your combination valve is bad. A booster just assists your braking operation. If your rear brakes are way out of adjustment this will also give you a low pedal
     
  9. MudFrog

    MudFrog 1/2 ton status

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    This is the same exact thing that was happening to me. I tried replacing the MC several times, then upgraded to a 1 ton MC and booster and it still did not help. I had good pressure up front, but nothing but tiny little dribbles of fluid out of the rears. There wasn't near enough pressure to bleed the brakes properly. Finally I ended up gutting the PV (removing the little plate at the tip of the rear nozzle that restricts the flow and my pressure is just as good as the fronts. I would highly recommend you trying this, it took me 3 weeks of not driving and 9 months of a very soft pedal to figure it out.
     

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