55 olds 88 custom. Fatman front with 69 Chevelle calipers, custom 9" rear with speedway rear caliper kit (Seville calipers with parking brake). Corvette MC from CPP and PV4 disc/disc prop valve. Bled my brains out, no pedal, bought the Motive pressure bleeder, got a decent pedal, but as soon as I start the car, pedal goes to floor. Will pump up some, but very weak and almost on the floor. Rear parking brakes are adjust really good. I move the lever 1/4" and both sides lock up the rotors, Called CPP, and they thought the MC might be bad because it sat for like 4 years, so I bought a new one. Installed it today, pressure bled all 4 corners 3 times, and it's no different. I welded some flared lines to up plug the front lines at the proportioning valve and now I have a pretty good pedal even with the car running. Pedal holds as well. So, it seems like it's the front? Not sure what I'm supposed to do or look for? No fluid leaks. Pads contacting the rotors. Could it be the prop valve? Really frustrated. Appreciate any thoughts.