85 Chev Silverado- 1/2 ton if it matters. Changed pads and shoes, had drums and rotors turned. O'Reilleys said that that would be the last turns on each. Started because of low pedal pressure. Still have it. Changed master cylinder. Bled it on the bench. Plugged line holes and pushed plunger in slowly many times until it firmed up and no air came out of bores inside. Bled brakes. R/R, L/R, R/F, then L/F. Couldn't get the left rear to stop bleeding air. The right rear went ok but the left wouldn't stop. Had the tube inside a cup of brake fluid to see the bubbles. Had the Mrs pump the pedal til it firmed and then I cracked the bleeder, let the fluid (or air) stop, closed bleeder, she let off the pedal. Pedal firms up no problem without truck on, but as soon as I turn the key, it dives to the floor. It goes down to where I can get the toe of my shoe under it and that's it. Anyone have any ideas on this one? I was told wheel cylinder but that it'd be leaking. One other thing. I tried the reverse and hit the brake thing to adjust the rears. It seemed to help but the brakes squeled when I was done. Could that be heat build up and rotors? I also adjusted them by turning the adjusters all the way out until I couldn't turn the wheel and then turning them back in until it would just turn. Both sides. Thanks.