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Thread: Low brake pedal

  1. #1

    Default Low brake pedal

    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 by chuckwagon; 11-21-2010 at 04:42 AM.

  2. #2

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    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. #3
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    Default

    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.
    Mike

    Currently

    1997 Chevy S-10 Blazer 4X4 with 330K miles and counting (Hunting rig).

    2009 Saturn Aura XE (wifes car)

    2011 F-150 Crew 4X4

    "Hold it to the floor till you see God.... Then Brake!!!!"

  4. #4

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    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. #5
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    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?
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  6. #6

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

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    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. #8

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    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. #9
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    Quote Originally Posted by 95RedBarn View Post
    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.
    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. #10

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

    Last edited by Brakeman; 12-03-2010 at 04:33 PM.

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