I own a 1997 Grande Prix. Occassionally I have no breaks. It makes a like crunching sound when I press on the brake pedal and I have no brakes. I press a few times and they would come back but not all the time. I have had the master cylinger replaced and they bled the brakes, but it is still happening. Has anybody had this problem before? I need help because it is scary not knowing if you are going to stop or not!