Hi,I bought a 2003 ford Ranger XLT that had a leaking caliper and a seized drum. I replaced rotors,pads,calipers and both drums,so front to back brakes. When I got to bleeding I bled the lines but can't get a firm pedal. It's firm when truck is off but as soon as it starts it goes to the floor. The master cylinder might have gone empty while the caliper leaked so could I have air in ABS? Any help is appreciated.