i have an '86 bonneville that i just replaced all brake lines on. also replaced wheel cylinders. front calipers are still fairly new. no leaks detected in master cylinder, which is probably original. after replacing lines and wheel cylinders, i bled the brakes. i bled them by having one guy working the pedal and one opening the bleeder screws. the process was a as follows. pump the brake pedal then hold it down. while the pedal is held down, bleeder screw is opened and pedal drops to the floorboard. with pedal still down, bleeder screw is closed. we repeated this process on all 4 wheels until no air comes out. With the car off, the pedal is high and firm. however when the car is turned on, the pedal drops to within an inch or two of the floorboard before it stops. when the pedal does stop it is firm and the car stops quite well. This seems to happen on all cars that i bleed brakes on so im not sure if im doing something wrong or not, thats why i tried to include most details of how i bleed the brakes. my question is, how do i get the pedal to firm up where its supposed to, closer to the top of the brake pedal's travel? any suggestions would be helpful to this extremely frustrating problem.