Question about 1987 GMC Suburban

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Rear brakes won't work

The front brakes are doing all the work. I can only get the front brakes to lock up on grass or gravel rear not at all. I've been fighting this all summer.
3 master cylinders, 1 used 2 new, used brake proportioning valve (off working Burb) new front brake calipers, new rotors and pads. New rear wheel cylinders. New brake booster, new brake hoses front used hose on rear.
I have disconnected every thing and blew air thru the lines looking for debris. Bench bled the master cylinder, let the fluid run thru the system for hours at a time, tried to use the pump and bleed. I've had it to a local garage, a very good mechanic.He can't figure it out ! Local Chevy service manager knows me well enough to say "If you can't get it fixed, I probably can't help you". I'm not a novice. I'VE worked at a GM dealership myself.
There are two brake systems for this listed as build options. What are the differences in the master cylinders? The rear brakes on my Burb are the larger and match the build sheet. Is there a third something GM is not telling me.

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  • Roberta Smith
    Roberta Smith May 11, 2010

    Sounds like you have replaced everything that can be replaced.... only thing i can think of is when the vehicle nose dives on hard application of the brakes a line is being pinched. If you were to lose fluid or a failure in half the master cyclinder.... you would have two brakes that work.... but they would be diagonally across from each other. Examine the brake lines to make sure that they were hooked up with that in mind.




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This is just a shot on the dark but did you use a low end brake fluid as this has been known to cause braking problems.

Posted on Oct 15, 2008


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