brakes?????

[1979dbkohl]

I have a 79 malibu and one day I'm driving and I go to stop and pedal went to the floor. So far I've put two rear cylinders in two rear brake lines new rear rubber hose. And still spongy pedal. Today I put on a new master cylinder bench bleed it and bleed all the wheels . Now when the car is off pedal is tight and perfect. When I start the car the pedal becomes spongy again I don't get it what a I doin wrong? Getting frustrated. Please. HELP. Thanks
Stock disc/drum also when I crack the fronts open the pedal squeezes air out. The rears when I crack them open the pedal doesn't move. Nothing squeezes. Please help

 

[lasttime78]

Sound like your Proportioning Valve is bad, or you have alot of air in your system. I have had that happen before myself. I bled the system rr firstlr next,rf,and then lf and two and half big bottles of brake fluid. All new brake fluid in system, well worth the work. Good luck.