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Thread: brake problem

  1. #1

    Default brake problem

    when my engine is turned off my brake is as solid as a rock but when i start my engine my brake goes all the way to the floor
    i have replaced my master cylinder, my brake booster, new wheel cylinders, blead all the lines
    can someone point me in the right direction to solve this problem
    1988 GMC Suburban V1500 Sierra Classic 4x4
    w/ 2" lift, 89 SBC 350ci
    Rear axle is a 10 bolt with 28 spline axel shafts posi-tracktion
    Transmition is a 700r4/4l60 with a np208 transfer case
    the brake system is a JB5

  2. #2

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    Quote Originally Posted by Tarsis View Post
    when my engine is turned off my brake is as solid as a rock but when i start my engine my brake goes all the way to the floor
    i have replaced my master cylinder, my brake booster, new wheel cylinders, blead all the lines
    can someone point me in the right direction to solve this problem
    Well, since it doesn't move with the truck off, it's not a leak, or an air bubble. Your ABS system or poportioning valves could be bypassing all the time, causing a re-circulation in the brake system.

    When the pedal goes to the floor, do you get any stopping power at all? Or is it just weak? Estimate for me in percentage of previously available stopping power.

    -Matt

  3. #3

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    Quote Originally Posted by mateospeed View Post
    Well, since it doesn't move with the truck off, it's not a leak, or an air bubble. Your ABS system or poportioning valves could be bypassing all the time, causing a re-circulation in the brake system.

    When the pedal goes to the floor, do you get any stopping power at all? Or is it just weak? Estimate for me in percentage of previously available stopping power.

    -Matt
    ok i do have some stopping power not a lot its about 25% of what i use to have it dos not stop like it is supose to

  4. #4

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    Pull the wires off of the abs unit and give it a try. Those ABS units go bad, but you can drive it with the wires disconnected. I drove my 92 blaser for years like that.

  5. #5
    Sr. Apprentice tommyboy's Avatar
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    Default

    I had a similar problem and I know this might be a stupid response but are the rear shoes adjusted right, manual ones will have to be adjusted. If there automatic squirt a small amount of oil or lube on them and make sure there moving. The best way to adjust the automatic adjuster is to pump the brakes while backing up. Works on the automatic adjusters everytime.
    1998 Chevy Z71 Ext. Cab
    2010 Ford Fusion SE
    2001 Yamaha Kodiak



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  6. #6

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    Quote Originally Posted by retired View Post
    Pull the wires off of the abs unit and give it a try. Those ABS units go bad, but you can drive it with the wires disconnected. I drove my 92 blaser for years like that.
    i dont have abs it was not an option for my 1988 berbon

  7. #7

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    I had a similar problem like this with my suburban but it doesn't sound like you are leaking any fluid as I was leaking fluid but did not realize it. My suburban was leaking a bit of brake fluid within the rear drum brakes thus saturating the pads. I finally realized I was leaking by checking the master cylinder over time as mine has a separation wall to prevent the front and rear brakes from completely leaking all of the fluid out.
    K1500 5.7L Chevy Suburban
    290000+ miles
    K&N CAI
    Black Bear Performance Tune
    TCI Servo and Shift Kit
    Long Tube Ceramic Pacesetter Headers
    Custom Side Swept Dual Exhaust
    Dual 2.5in electric DMH Performance Exhaust Cutouts
    BFG A/T 285s

  8. #8

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    Quote Originally Posted by Tarsis View Post
    i dont have abs it was not an option for my 1988 berbon
    Hmmm... Forgot about that. Try blocking off the front brakes (using line locks), then the rears, to see which end the problem is on.

    If it was a brake adjustment problem, it'd happen all the time; not just when the car was on.

    You have 4-wheel drums, correct?

    I would check your porportioning valve; it's most likely bypassing. I'll think about this some more.
    -Mateo

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