Low brake pedal

Discussion in 'Lifted & Offroad Suspension' started by chuckwagon, Nov 21, 2010.

  1. chuckwagon

    chuckwagon New Member

    I have a 1992 GMC 350 Sierra pick-up truck....automatic, air, two-wheel drive

    A couple months ago I "braked hard" on the highway and noticed a loss of brake pedal immediately after that.

    I still have brakes, the pedal just goes half-way to the floor.

    This is what I have done so far that has NOT SOLVED the problem...

    *intalled new master cylinder

    *installed new rear brake shoes

    *bled the brake lines several times

    *adjusted the rear brake shoes to where they are very close to the drums

    *checked the vacuum booster and it is working

    You can tell the vehicle does not have FULL BRAKING power like it once had. I can still brake enough to "get by" but it is not the......"slide the tires" stopping power like it was before this happened.

    I have asked about this before and have re-bled the brakes and re-checked the vacuum booster. No change.

    If you could provide some insight, it would be appreciated.

    Thanks, Chuckwagon
    Last edited: Nov 21, 2010
  2. 95RedBarn

    95RedBarn New Member

    I have the same problem with my 95 4x4 and I have changed damn near everything in the brake system except the rear wheel cylinders. I find that if I pump the brakes a bit they do grab alot better. But other than that Im just as stumped as you I guess :s
  3. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    Have either of you done anything with the brake proportioning valve?? since the rear brakes are what give you a firm pedal, and the front just take the pressure from there... And if the rears arent gettting enough pressure then you have the issue with the pedal "sinking" like you are both describing.
    Also with the 1995 if you have ABS i believe the have the be power bled by the dealer to be right. It might have been 1996 but id double check to be sure.
  4. 95RedBarn

    95RedBarn New Member

    Yes I have tried another proportioning valve myself...everything but rear wheel cylinders and front calipers, Ive dove the booster, master, prop valve, couple lines between, lines from prop to rear drums, front discs and pads, drums and shoes looked new still but adjusted them, bled the system countless times. I do have ABS but pulled the fuse because with it in the brakes hardly work at ALL (hit a friends car with thefuse in...it was out when I bought the truck)
    What is "power bleeding"? Ive never heard of such a thing :s
  5. stephan

    stephan Rockstar 4 Years 5000 Posts

    GMs' Tech 2 bleeder is what Mike is talking about as far as power bleeding. It's the only way you can get all the air out of the ABS. Have either of you ever looked at the pin on the end of your prop. valve? I asked Chuck on the other thread he started about this problem but he didn't answer. Is your pin out, in, or flush with the end?
  6. chuckwagon

    chuckwagon New Member

    Hey Stephan, I took off the rubber cap on the end and the pin is FLUSH with the end. What do I do now?
  7. stephan

    stephan Rockstar 4 Years 5000 Posts

    If your pin is flush with the end this is ok. If the prop valve is stuck foreward the pin would be sticking out beyond the valve.
  8. 95RedBarn

    95RedBarn New Member

    Mine is also flush...I dont know about the one I originally took off the truck thought, but it didnt change my braking at all when changed.
  9. stephan

    stephan Rockstar 4 Years 5000 Posts

    Since both of your pins are flush, & you have replaced the prop valve & both you & Chuck have replaced or tried everything else, about the only thing this leaves that you two haven't done collectively is the bleed with the GM Tech 2 bleeder. Someone said GM charges about $100. for this, but it is about all that is left to try that I can think of.

    One poster said there is a "shadetree" way to fool the abs. He said to take your truck out to a dirt road 25 to 35 mph, and slam on the brakes quite a few times to activate the abs. He said doing this numerous times can sometimes get the air "through" the abs while it is activated & push it farther on into the lines where it can be bled out through the normal brake bleeding procedure. I'm NOT recommending either of you try this, & of course if you did you would have to be very carefull, but it's the only other thing I have heard of that might be worth a try.
  10. Brakeman

    Brakeman New Member

    Adjust the booster actuator out a 1/4 turn or so. Your emergency braking probably moved the booster hold down.

    Last edited: Dec 3, 2010

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