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HELP HELP HELP Brake proportioning valve troubles!!!!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Bigmeats, Mar 17, 2001.

  1. Bigmeats

    Bigmeats 1/2 ton status

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    I replaced the rear wheel cylinders today and broke one of the rear brake lines. Most of the fluid in the rear of the master cyl was drained because of the broken line. I replaced the line and the rear wheel cylinders, and went to bleed the brakes and now cant get any pressure to the rear lines. I have good pressure to the prop valve but nothing going to the rear of the truck. Also the brake lite has come on in the truck. My Bro in law who is a wrench by trade thinks there is a pin in the prop valve that cuts off the flow of brake fluid to the rear if you were to blow a wheel cyl while driving so you could still have some front braking. Is this true? is ther a way to re set the pin if this is the case? Of course no auto part stores carry the valve its probally a dealer item. I should also mention the master cyl is fairly new, about 15,000 miles on it.

    Any help would be great!!!

    Bigmeats


    Carl Fiocca...Manhattan Il...75 Blazer
     
  2. MudRebel350

    MudRebel350 1/2 ton status

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    That is true, you have to open the prop valve to bleed the rear brakes. If you need a new one there about 80 bucks. Im not positive on how to do it but Im sure its self explanitory if you look at it.

    JD
     
  3. jerseyk5

    jerseyk5 Registered Member

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    I had the same thing happen about 2 years ago. Yes, there is some kind of pin or check ball in there. You have to get it back to center. Im not positive, but I think you have to open both your front bleeder valves and pump the brakes a couple times. That should reset that little pin. Then close your fronts and go about bleeding your system. Like I said, Im not positive but Im pretty sure thats what I did. Good luck!!!
     
  4. thebigdaddyof2

    thebigdaddyof2 1/2 ton status

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    Hey Carl,
    Not sure about the "cut off pin" in the prop valve but what would be the difference if you were not replacing the master cylinder? You should have an air pocket that has to be bled out in some fashion. Did the rear reservoir go completely dry? When you pump the brakes and hold them, can you break the fittings loose before the prop valve, after the valve, and at each of the wheel cylinders to check for fluid/air? If the system did in fact go dry, you may need to bleed the system in sections starting at the master cylinder and working all the way to the wheel cylinders. This may require several bottles of fluid and a lot of patience. HTH. todd
     
  5. K10

    K10 Registered Member

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    If you look at your proportioning valve there should be a rubber cap over a small brass pin. It is on the left hand side. Take the rubber cap off and have someone push the brake pedal and hold it to the floor. A small pin will move out of the vavle. You need to hold this pin out while you bleed your brakes. (A pair of vise grips works good to hold the pin out.) you should do this with the key in the on position.

    <A target="_blank" HREF=http://nick.rockcrawler.com>http://nick.rockcrawler.com</A>
     
  6. BlazerBoy

    BlazerBoy 1/2 ton status

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    What do you guys think.. Carl is still having trouble getting his old valve to work. And a new one is 180 bucks. Do you think a newer 80's valve could be used I imagine he would have to reroute the lines but would it be safe and effective to do that? We are scheduled to leave for MO. this friday but he cant go without brakes.. :) Thanks for you help...

    BlazerBoy
    http://generalblueballs.coloradok5.com
     
  7. Triaged

    Triaged 1/2 ton status

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    I just did the brakes all around on my 71 on Sat. There was no fluid in the system at all! The front was easy to bleed but the rear I could not get any fluid to. I used flair fitting wrenches (so as to not strip the soft fittings) and started at the master and bled the rear line at each junction. After that The rear bled fine. BTY I also found out that I had a cloged bleeder in the rear but I don't think that was the problem because I tried both sides. Hope this helps

    '71 Blazer CST with alot of rust
     
  8. Blaze

    Blaze 1/2 ton status

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    My prop. valve cracked once. I just went to the junkyard and bought a new one. It only cost me about $25 there and I got it off of a low mileage truck.

    [​IMG]<A target="_blank" HREF=http://www4.ncsu.edu/~brschoch>http://www4.ncsu.edu/~brschoch</A>
    My truck beat up your SUV
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    Prop. valve is designed to cut off fluid to whatever end (front or rear) fails. Supposedly they should self center with a lot of pressure..something like 450psi. Its in the service manual. The light is SUPPOSED to come on, (the system has failed basically) just no one leaves the key on when bleeding brakes...

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     

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