i have a 89 base 2wd d21 .....i replaced a not that old (2yr.) front brake caliper that froze up, passenger side, then replaced the passenger rear side brake cylinder when the bleed valve broke off. i tried to gravity bleed it twice but pedal remained soft initially. bled the old school way, and it's better but still goes to the floor (with resistance) the first pump, then is very firm as long as i hold it. after 30 seconds, the pedal goes back to the floor again. i don't seem to be losing fluid anywhere. my battery was too dead to start the car after bleeding the brakes (does this matter?)....i'm thinking master cylinder, now. any thoughts or suggestions about how to check it or any other helpful comments?