I have an '86 F-250 with about 130,000 miles. I use it to pull an Alumalite fifth wheel. I have problems with braking. The pedal goes closer and closer to the floor until I pump it up. The fifth wheel has its own brakes. I use a Prodigy controler. The truck has a relatively new master cylinder and hoses. It wasinstalled when I purchased the truck from a local mechanicin '04who I feel knew what he was doing. The truck sits a lot and has been used to pull a 31 foot trailer a couple of thimes and the fifth wheel maybe five times on relatively short trips. I replaced the master cylinder after having a brake involved accident with the trailer. The only other use of the truck is to take it for a good run once a month and for the annual dumb runs. Any thoughts on what is causing the brake problem. Note. the brakes are really squishy even whn I am not pulling a trailer, but I understand that is common in the diesel. THX J

 

Maybe the brakes weren't properly bled (on the truck) after the new parts were put on. ABS can sometimes make bleeding more complicated.