My name is Rob and I have a 2000 Cadillac Seville STS. My master cylinder went when I had a ruptured brake line. I replaced the brake line and master cylinder(bench blead) and blead all the air out of the line. The pedal still goes down to the floor. I figured the new master cylinder may have been a dud so I took it back and put another new one on and the same thing happened. I also gravity bleed the system. If you think you may have an answer Please respond when you can.