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Q: Rear brakes not grabbing - 1995 GMC K2500

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I am having trouble with my rear brakes not grabbing very well. I set up the rear on jack stands and could hardly stop the rear wheels with the brake pedal. My front brakes are in good condition and lock up in gravel, but not the rears. I bled the rear brakes with a pressure bleeder and the fluid came out with no bubbles. The brake pedal is firm. The master cylinder looks like the original. Can the master cylinder fail for the rear brakes? Could it be the proportioning valve built into the Kelsey Hayes 4wal ABS system? Could the proportioning valve have an isolation circuit that is stuck isolating in one of the brake systems? Do you have any ideas? Thanks.

Hello. It is not in the ABS, but may be the proportional valve not giving the correct pressure split front to the rear. The vehicle never had enough pressure for the rear brakes. Have the rear shoes adjusted properly if you have drum brakes. You should check to see if there is an updated part to replace the old one. If you would like to have this done, a certified technician from YourMechanic can inspect the brake system and let you know what repairs are needed.

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