I don't know what's causing this, but, I drove her 80 t'day and it scared the crap out of me. What I've noticed; Seemingly random loss of pedal pressure. Sometimes it will stop fine and other times I have no brakes. ABS activates and I have no stopping at all. Maintains pedal pressure when engine is off. Pedal almost goes to floor when engine is on. Pumping the pedal doesn't seem to make a difference. Brake fluid level is high and doesn't change. No leaks. Newer OEM rotors on the front and 100 pads. Newer aftermarket rotors on the back w/ new pads. This appears to have come on slowly, but, is increasing in frequency. Disabling ABS mkes no difference. My initial thought was that my aftermarket rear rotors were not thick enough and therefore I needed more pedal movement to engage the pads. Then when I tested the pedal pressure with the engine both running and not I am now wondering if it's possibly a brake booster problem because that would only be active when the engine is producing vacuum. The other thing I was thinking is that it could be master cylinder issue. Once again there isn't any fluid leakage either inside or out. Whadya think?