1994 Silverado front brakes locking up

[Sksewell]

Both front brakes on my 1994 Silverado start to stick and lock up after driving a short time,  making the petal stiff. Opening the bleeder valve on one side releases both front brakes. Releasing the bottom line on the proportioning valve will also release both brakes. Calipers and pads have been replaced and rotors have been turned. All rubber/flex hoses connecting to the caliper have been replaced as well. Not sure if it’s the master cylinder, proportioning valve, or booster. Backstory: the truck sat for awhile with contaminated fluid. Since then, the fluid has been flushed multiple times. 

[Nigel Snyder]

I have a similar issue ans situation. I have posted here and two other forums. I'll update you if I get any helpful info, good luck

[jay709]

check brake pedal for full return, l’ve seen the older style brake light switch keep brake pressure on just because switch was misadjusted, brake lights were off. there may be something causing your pedal to not fully return, just lay under there  pull up on pedal, its 5 minutes and may reveal something

[Dr.Jimy]

The rear brakes have  a self adjusting mechanism that will not keep up with the wear they get. You have to back up and hit the brakes hard several times to make them adjust. It takes no time and they are out of sync. again. Mine is so bad that on ice the front wheels are locked and the rear are still turning so the only solution is keeping it in 4x4 under those circumstances. And other than that back up and hit brakes hard whenever you think about it , you can also feel how out they are from brake pedal resistance once you do this.

[Mikebtte]

If you loosen the master cylinder in the booster a few turns do you still have the same issue? Sometimes the needle on the back side becomes out of adjustment and causes the front breaks to lock up. If adjusting solves the issue, This is normally signs of a failing booster.