front left break stick

[sierragrove]

So I have had a problem with my front left break sticking ever since I changed my master cylinder in my 2005 sierra 5.3 z71 1500. Vacuum assist, rear drum, front disk. When the master cylinder went bad, causing the breaks to stick on, I was traveling on the hwy and caused the breaks to heat up and melt the rubber boots for the caliper pistons. So to date I have replaced caliper, rotor, rubber hoses, pads, ABS modulator and flushed entire system ( yes I bled the system of air). After replacing each component nothing seemed to fix the problem and it is still a problem. The only thing left to replace is the break booster and the proportioning valve. Any thoughts?

[Doug_Scott]

Not to be picky, but it's brake.  Believe it or not, but it makes it hard to read when spelt that way. 

If only the left front wheel is doing this, and no there, do not waste your money on parts that impact the entire system only, like master cylinder, booster, proportioning valve, etc.  The common causes for one wheel sticking is the flex hose, caliper sliders, caliper piston/seal.   The combination valve combines proportioning valve and pressure differential valve.  Have you taken a good look at the right rear brake to see if it is running hot? 

When the brake has gotten to the point you can't rotate the wheel, open the bleeder and see if it releases.