Brake pedal going to floor

RODGERH1

MEMBER
1999 FORD F-150
5.4L
V8
2WD
AUTOMATIC
150,000 MILES

Brake light came on. Needed brake fluid. Filled brake reservoir. Light went out. Everything okay. Two days later brake pedal felt mushy. Pedal eventually going to the floor. Replaced master cylinder. Pedal still going to floor. Found driver side rear wheel cylinder leaking. (Ah ha. That is what the problem has been all the time.) Replaced wheel cylinder and put new brake pads on both back wheels. Bled air out of both back wheels. Pedal still goes to floor! Okay, bad brand new master cylinder? Got another new master cylinder. Brake pedal still goes to the floor! Two bad master cylinders?
Help. Mechanic with thirty years experience has no idea. He is our fleet mechanic keeping thirty vehicles going. From pickup trucks all the way through farm tractors, bulldozers, to over the road semi's.

1 Reply

MHPAUTOS

MECHANIC
31,937 POSTS

May still have air in system, did you bleed the master on the bench first? Also, try and isolate problem by using brake hose clamps and lock off all brake hoses. The pedal should be hard and firm, release clamps one at a time and see if pedal sinks all the way. I would also be re checking rear shoes and adjustments as well, just to be sure. Start here.