Brakes locking up

[nickelnuts]

I have a 1984 chevy k10 with the 6.2 diesel. Been having the front brakes locking up after about 20 to 30 miles. They will release after 30 to 60 minutes of not driving.. I have changed both calipers pads master cylinder and the hydroboost unit and both rubber brake lines to the calipers.

 

[fast 99]

Apply brakes then open bleeder on caliper. Is residual pressure present and when doing that do the rotors turn freer? Description sounds like something isn't allowing all the fluid to return. Takes very little pressure for disc brakes to drag.

 

[Dmack]

I had the same occasional problem on my 83 that had been converted from diesel to gas. Still.has the hydroboost. Bleeder test would work, but still frustrating. One time it happened, I loosened the two nuts holding the master to the hydroboost, and it released. I made a .1" spacer from aluminum and put it between the master and hydroboost. Haven't had the issue sice (about a year now).

 

[Ricko1966]

I had the same occasional problem on my 83 that had been converted from diesel to gas. Still.has the hydroboost. Bleeder test would work, but still frustrating. One time it happened, I loosened the two nuts holding the master to the hydroboost, and it released. I made a .1" spacer from aluminum and put it between the master and hydroboost. Haven't had the issue sice (about a year now).

If the pushrod is incorrectly adjusted between the booster and the master it can cause this also on vacuum booster brakes. Not a bad idea,never thought of just backing the nuts off a couple of turns while the brakes were dragging to see if the pressure released.

 

[Dmack]

Pushrod isn't adjustable on mine with the hydroboost. Fought the lock up issue for a while before trying this. Haven't had the issue since.

 

[fast 99]

If you do suspect wrong pushrod there is a tag wire procedure to check it.

Takes 2 people. Remove all the fluid in the master. With a small piece of wire insert in the smaller front port. If wire can't be easily inserted, you have found the problem. Have the helper VERY slowly with hand only push down on the pedal. At the same time move the wire up and down until there is drag on it. That is the distance the pedal travels until braking action starts.

BE VERY CAREFUL, if the pedal is pushed beyond the point of drag the master will be ruined.