Just replaced the master cylinder and brake booster on a 96 chevy P/U - With truck off brake pedal is firm but when engine is started brake pedal goes to floor. - Bled brakes (three bottles worth- no bubbles) Can you help?
Bleed the master then you can gravity bleed starting in the r/r then l/r then r/f and l/f. Remove the master cylinder cover then fill. Looson the bleeder when you see all fluid and no air bubbles tighten the bleeder and repeat.