A few days ago, I drove my truck to my gym. When I was done, I started up my truck and had a very soft pedal. No indication of any problems up until then (no lights on, no vibrations, no noise). If I stepped quickly on the pedal, I had a somewhat hard pedal for only a few seconds and then it would start to soften up and go to the floor. My mechanic checked out the MC first to check on leaks, without seeing any, he checked out the lines (rubber and metal) and as far as he could tell, no leaks there. Bled the brakes, pedal was still soft. Decided it must be a problem with the MC. That was ordered and installed and still the problem exists. (Here is where my ingorance is going to show...this is what I think he told me)....

He thought it might be the ABS system. Something about the two lines coming out of the ABS: one for the back and one for the front. If the front line was blocked (?) the rear brakes worked well. With both lines opened soft pedal...

My F-150 is 2002-FX-4 Crewcab

Anybody have any suggestions or experienced something similiar? Need your help...my mechanic is stumped other that replacing the "box"...

 

sounds like maybe a slow leak at one of the front calipers? It doesn't take much to give a soft pedal... a few drips will do it.

 

It can also be the master cylinder bleeding back. If it were mine, I would inspect the calipers and if all looked clean and dry, then I would get a brake expert to take a look at it.

 

I've had the same experience before with a 97. I gave up and stated throwing parts at it. One day in a tantrum I smacked the 4wabs unit with a rubber mallet.:o I haven't had any problems since. That was about 6 to 10 months ago.

I've been looking for one of the units in the junkyard to take apart to see if they are repairable. Just haven't looked hard enough. But when I get one I'll check it out.

Edit
Also, I've seen post by jbrew that suggests replacing the rubber brake lines, they get corroded over time. He posted a picture in a thread a while back. But I don't remember what thread it was.