I have a '95 f150 ext. short bed. the brakes started to go soft. It felt like a typical master cylinder failure: push on the petal and get brake then it would fade. pumping the brake would not change the problem. I changed the master cylinder and the problem is the same. bleeding the system(several times)had little effect. I decided that I got a bad master cylinder and then replaced it again. I bled the braked and was able to get the brakes to go solid with a single and small pump after applying the brake. then a couple of day later I had to brake hard and now I am back to where I started with spongy brakes that won't pump up. I bled all four corners and the rabs. I prepared the master cylinder and got all the air out before installing it. there are no leaks at the wheels or any other place. the only two things I can think of are the proprotioning valve and the rabs system. the p-valve is on the rear portion only and the o-ring was replaced on install. any Ideas which or why?

 

Red I am haveing the same problem on my 92 F-250 . What did you do to fix yours?

 

I had that problem... put in a new master cylinder and it was better, but not fixed. Took it to the shop... they put a brake lock on it for an alignment and the front hose blew open. After new front hoses I have no problems. The hose that blew was swollen up. The other one was on its way out. Glad it happened at the shop. My lines were the ones that went from the frame to the front caliper. I had a 94 and was suprised that the brake lines would fail that early. The petal was mushy from the lines swelling.
Matt