Hi ya'll, first time in the nifty F150 forum, truck has been good to me till now, but now It's left me looking for advice. So the f150 started with a caliper that stuck and got hot, terrible luck as nothing was physically wrong with the brakes leading up to this. So I replaced both front calipers, bled it and couldn't get any pedal. The brake pedal would slowly creep to the floor. Seeing this symptom before on other trucks, I replaced the master cylinder thinking it got damaged somehow because of the brake failure. No improvement. Bled the ABS valve and brakes about a million times and even activated the ABS valve like the dealer says thanks to a buddy and a scanner. No pedal. Thinking the only way this could happen is a hard part failure in the ABS valve, I took it off and tried to replace it. Thinking boiled fluid may have done it makes sense since it is the closest to the wheel that got hot.

Ford could not get me the valve, it stayed on B/O and I made the parts guy call. The valve was a batch contract through I-don't-know-who and is no longer serviced. So I sourced a salvage unit. Put that valve on and bled everything. BTW, i had replaced all the rubber lines while I had it all apart and did the back calipers too, new pads , rotors, and hard lines up front. So everything bled good, excellent pedal feel. The ABS light was on and the ABS did not work however. Thought that was a programming issue, was going to track down my buddy again with the scanner and make a night to drive over to his place.

Didn't get that far, went to run the truck the other day, and it was like someone had flipped a switch, pedal slowly falls to the floor. Arrrrr
Thinking maybe driving it had released some air as I had not yet activated the ABS motor. Bled everything a million times over, no air, not sure what to think now. So finally get some pedal with the engine off, great I thought, must have been air. Wrong, as soon as I start the motor, the pedal slowly falls to the floor, even when I physically cannot make it with the engine off. It is like there is something in the ABS valve that has gone wrong and it takes the extra pressure of the booster to overpower a valve or check or seal of some sort.

So now I still have no brakes and the truck is down. Where should I be thinking next? It has got to be the ABS valve, correct? With caps on the lines the master cylinder is solid pedal. Did I miss something in this process?

 

Have you looked at/tested your vacuum booster?