05 Trailblazer brakes are constantly deployed. Runs good first couple of miles the. Brake pedal gets hard and truck will come to a stop if not giving it gas. Drive it til it locks up and got tires in the air, all 4 are locked up. Calipers are New. Brake Lines are New. Bad ABS sensor, Hubs were replaced. ABS disengaged by removing fuse and still does same thing. If Master Cylinder or Booster were bad I'd have less or no brakes... My problem is too much brakes. Any Ideas?

 

Are all the brakes locking up, or just one or two? My advice at the moment is to buy an inexpensive infrared thermometer and when the brakes get hard, pull over and take a temperature reading of all 4 brakes. That will tell you if it's system wide or just one or two brakes.

 

Hello Flyboy2610. It is definitely all 4 brakes. Going to try and vacuum bleed master cylinder and if that doesn't work I guess I'll change out the only 2 components I have replaced... The Booster and the Master cylinder. I'm at wits end. Never seen this before.

 

I have read that a bad valve in the booster can cause the brakes to 'self apply'. I've never had it happen myself, though. The wrong pushrod length between the booster and MC can cause sticking brakes, too, but that's more of an all the time problem.
From all the work that's been done it's probably a safe bet that the brake fluid is new. I would try replacing the booster first.

 

Correct flyboy the fluid is clean and no signs of leakage anywhere. I've read that tiny bubbles in the MC can also create issues with the braking so I will be vacuum bleeding that first. If that does nothing, MC and Booster are next. Going to be a fun weekend... Thanks for the feedback

 

Good luck with it!