The right front brake locked up on my car and I replaced the caliper because it was frozen. The problem seemed fixed until about 2 weeks later it happened again. You can pull over and shut the car off for about 3 or 4 minutes and the brake will release and you can drive it again. It does not happen very often. Being that it only involved one wheel I do not think that it is the master cylinder. I have ordered a new brake line from Chevrolet and I hope this fixes it. I also think it may somehow involve the ABS system not sure yet. I will let you guys know as soon as I replace the brake hose.