I have a 1978 Malibu. I swapped the rear end for a 9" from Quick Performance. I used the calipers they gave me without parking brake. I have the stock brake booster original to the car. I did switch the brake proportioning valve to a disc/disc valve. The master cylinder is the stock one (disc/drum), but it is brand new. I have bench bled the master, twice (the most recently with the syringe method) and bled the brakes with a Motive Power bleeder three times at 15 psi. I feel like I have some pedal until I start the car. When I start it up, the pedal goes to the floor. When I put the car in reverse, on the jack stands, the rear wheels won't stop turning when I apply the brakes. I really don't feel like I have air in the lines - I've been pretty thorough. I am a researcher, and I have heavily scoured all the posts I could possibly find, with inconclusive results. The conclusions that I have drawn is that either the master is not pushing enough fluid to make the rear calipers clamp down, or the master pushrod is too short, but I think that is a longshot, because everything I'm using (booster and M/C) are parts specific to the model year. I am wondering if anyone else has had this problem, and if they've had any success. I just bought a new master from an 85 Eldorado hoping that the disc/disc master might solve the problem, but it didn't fit the booster. I'm feeling that I'm using the wrong master for the system, but I need to maybe find a master that would fit my booster, as it seems to be working properly. Any help or suggestions would be greatly appreciated!! I've been putting this thing together for a year, and I am so close, but I'm afraid to drive the thing with no rear brakes.