break proportion valve bad

10

Asked by Mar 05, 2016 at 06:00 PM about the GMC Sierra 1500

Question type: Maintenance & Repair

when I step on my brakes the brake calipers
lock up in the front, really bad the first time
and won't release, I completely flush the
system several times with brand new dot3
brake fluid, I replaced both calipers on the
front, no luck, I replace both rubber brake
lines in the front, no luck, I completely
rebuilt the break master cylinder, still
locking up, when I open the proportioning
valve while the calipers are locked up they
release, is my proportioning valve bad? and
what are everyone's thoughts on getting
one from a junkyard I've heard bad news?

2 Answers

100,495

You didn't state what year, but wrecking yard valves tend to have problems, have you checked for an aftermarket valve?

10

1991. brand new ones are about $110 plus the shipping each, I'm taking apart the proportion valve now, can't seem to loosen the threads to the back brakes, it's a SOB, I had some rust bolt loosening oil which I squeezed on it, I took the front and rear springs out of the proportioning valve but if you look into the middle where the brake light sensor is if it grounds, it looks all black and gooey I'm trying to get everything out and then clean it put it back together.

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