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Brake woes...

Discussion in 'Chevy Trucks' started by Big Todd, Mar 9, 2003.

  1. Big Todd

    Big Todd Senior Member
    Messages: 126

    I have an '87 3/4 ton, blah blah blah... standard issue old "reliable" plow truck.

    A few days ago, I accidentally cut one of the brake lines going to the back. (don't ask how, it's a long story) I replaced it without too much trouble, but could not get any preasure in the system. Then we noticed a wooshing sound coming from the power booster, which I suspect had been on the fritz to begin with. So I replaced the booster and master cylinder. I bled the whole system and I get a good stream on the fronts, but only a trickle out of the backs. pedal preasure is good when the truck is off, but as soon as you turn the engine on, the pedal goes all the way to the floor and stays there until you turn it off and then it comes back up.

    Any ideas at all? Am I just not being patient enough when bleeding the rears? Could I have a pinched or clogged line somewhere? I am at a loss and since I spent a lot of time this weekend working on it when I could have been doing other things, I am ready to drive the thing into the lake behind my house.:realmad:
  2. wyldman

    wyldman Member
    Messages: 3,265

    It may be a stuck proportioning valve.You can tap it with a hammer gently to help it centre.

    Try gravity bleeding the rears for a while.It's a long line to the back,so just let it run out slowly,with the master cap off.Then bleed them normally.Pump the pedal slowly,so you don't suck air in,or damage the new master.You may have to try for a bit,but they should eventually bleed.As the air gets out they will become easier to bleed,so try the gravity bleeding first.

    Also check your rear brake adjustment.If the brakes are adjusted up properly,it will be easier to bleed and your pedal travel will be much less.
  3. bls47303

    bls47303 Junior Member
    from indiana
    Messages: 4

    we havve had problems with a soft prdle when the engine is on and it turned out to be a leaking wheel cylinder on the rear. take the drums off and see if the inside is damp/wet
  4. paul soccodato

    paul soccodato Senior Member
    Messages: 430

    definitely, sounds like the proportioning valve.
  5. plowking35

    plowking35 2000 Club Member
    from SE CT
    Messages: 2,923

    I did the rear brakes on my 89 2 weeks ago, a few things will cause a soft pedal.
    Broken brake line, but sounds like you have fixed that.
    Leaking wheel cylinders
    Once the new brakes are installed, adjust the rear brakes till the drums just start to rub.
    The porportioning valve could be offset to compensate for the rear line breaking.
    I found with the 89 that once the brake line that we broke was fixed and everything reassembled, we then bled the sytem, and had good flow of fluid but still a very weak pedal, by adjusting the rear shoes, the pedal came right up to the top. I would start there.
  6. Big Todd

    Big Todd Senior Member
    Messages: 126

    Thanks for the comments guys.
    I bought a vacuum style bleeder kit and went to work on it last night. Still getting very little out of the bleeder screws, so I undid a union on the line that I replaced and found I am getting full preasure up to that point. So, I'm thinking that either I have a piece of crud in the line or I accidentally kinked or somehow bent a line to the point that fluid won't flow. I'm going to try relpacing the line from that point back and see what we get.

    If it weren't suposed to freezing rain tomorow night and Thursday, I'd leave the damn truck sit until mid summer and I could stand to look at it again. But alas, it is our only truck with a salter on it...:realmad: :D :eek:
  7. chevy

    chevy Member
    Messages: 33

    I had a C-30 that I turn into a K-30, but thats another story. I had a simular problem. After thinking I tried everything in the book, a old timer suggested that when I bleed the rears that I open the bleeder then depress the brake pedal, close the bleeder release the pedal and do this until a good stream comes out. Amazing enough it worked and still have good brakes still. I haul a 8' foot Fisher and a 2 yd. Henderson sandeer I usually weight in about 12000 to 13000 when I pull off the scale after loading up with sand/salt. I have a 350 w/700R / 208 borrowed this from a Surburban "86" that I bought for a donner truck 3 years ago. Doesn't take a licken, but still ticken
    Chevy/GMC like a rock:waving:
  8. Big Todd

    Big Todd Senior Member
    Messages: 126

    Hey, I got her fixed!:D

    It ended up that the proportion valve was stuck so as not to allow the fluid to go to the rear brakes. There is a reset valve on it and once that was set we tapped on it with a hammer and mashed the brakes a couple of times and bled the system. Viola', brakes!:drinkup:

    Thanks for all the suggestions.
  9. wyldman

    wyldman Member
    Messages: 3,265

    Glad to hear it's fixed.9 times out of 10 it's a stuck proportioing valve.