The other day my front brakes seized up smoking the pads. While waiting for the tow truck I shut off the car, when I started it again, the brakes where fine, spongy, but fine. I am a cautious person, so I had it towed home and begin working on it. I replaced the calipers, rubber brake lines, pads, rotors, bearings and speed sensors ( I know the bearings and speed sensor is one unit). I reloaded the calipers and bled the brakes, for what seemed like forever. The pedal went all the way to the floor, I bled them again, but the pedal still went to the floor. After some online investigation, I determined that my ABS control valve was bad. I went to my local parts store (salvage yard) and purchased a new (used) master cylinder and ABS control valve module. Bled the ABS module, bled the brakes once again, but the pedal still goes to the floor. When the engine is off, the pedal is stiff, but when it is running, the pedal goes to the floor. The booster has vacuum and the check valve is working good. Now the ABS and brake light is on. This is the limit of my knowledge. Anyone know what is wrong?

 

Sounds like one of the rams stuck and wasnt releasing, not mentioned in brake rebuild. Disc brakes will always slightly drag but wheel will turn freely. By now brake lines are probably full of air and usually that will migrate to the furthest line(s) (rear) from the master cylinder. Possibly that's defective, not mentioned either?

Rams can have internal rust buildup if fluid has or had a moisture content and stick, not release pressure. Used to use C clamp to compress those for pad change. Have had this Problem on my '79 'Lil Red Express Truck. So would be my guess, other better answers may or may not follow?

Photo below, no longer have of coarse. 360CID motor but only rated 225HP, can be had these days maybe around $20K- paid $10K back in '79. Just keeping post interesting.