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Q: Brakes grab and lock up occasionally - 1990 Chevrolet G30

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My van has a hydroboost system. Ocassionally, I have problems with the brakes that grab and lock up. I've noticed this at the front ones. The issue would improve if I let the van sit with the pressure bleeding out, but only for several days and then the problem would return. Also, I had the front brakes bled. The brakes wouldn't release right away when I opened the bleeders. When the problem occurs, there is no brake system warning light on. What might be the cause?

Make sure the brake pushrod has some freeplay, how ever small. Also check the "check valves" on the hydroboost system to make sure they are releasing residual pressure appropriately.

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