Hi TARHEEL1. Welcome to the forum. I can't speak directly about your model, but for many years GM has used a step-bore master cylinder that has a valve system that will block any passage that doesn't build up the same pressure as the other ports. This commonly happens when pedal-bleeding the system with a helper. It seems this happens less often if you never press the pedal more than half way to the floor. That is good practice anyhow for any car because debris and corrosion build up in the bottom halves of the bores where the lip seals don't normally travel. Running the seals over that crap can rip them leading to a slowly sinking pedal.
Once that valve trips in the master cylinder, you won't get any fluid flow to that caliper. The other half of the system will seem to work fine and most people don't notice the loss of braking power. The symptom is the pads on one side wear out very quickly and the other side looks like new. MANy people finally realize there is a problem by the time this happens the second or third time.
The only I found to reset the valve is to open the bleeder screw for the caliper that won't bleed and give it a short burst of compressed air, then let it gravity bleed. If you fill the entire line with air, it sometimes will not gravity bleed unless you irritate the master cylinder a little by pressing the brake pedal down an inch or two by hand. Once it has gravity-bled a little, close the bleeder, then stroke the brake pedal just a few inches to push the pistons out but not far enough to trip the valve again. Open the bleeder once more to remove the few little air bubbles and you're done.
Tuesday, June 8th, 2010 AT 5:09 PM