Since I had such good luck with the prior question I think i will try again. Same truck 1996 F250 Diesel has a spongy brake. You can pump the brakes and they get hard as a rock, but it loses hardness very fast. If you slowly press the brake pedal it will go to almost the floor before stopping. My first guess would be Master cylinder? Prior owner said the ABS warning light was on (2 weeks ago)and he replaced the sensor at the rear end and the warning light went off. Thanks for your help in advance. Maxx

 

You can check the M/C by removing the two nuts holding it in place(leave the tubing connected). If its leaking, the booster side of the flange will be wet around the piston. The fluid will be leaking into the booster. Hope this helps.

 

thanks for the advice. I do also notice that at the end of the master cylinder (closest to radiator side) on top there is a connection of something that is wet with brake fluid. IM not a mechanic so I dont know what that is. I assume seeing any wet spots of brake fluid on the master is not normal. thanks again maxx

 

The connector on the front of the master cylinder is the cruise control disengagement switch. It disengages your cruise control when the brakes are applied. If it is leaking, replace it and see if that solves your problem. If not check this: https://www.ford-trucks.com/forums/6...-problems.html

 

Yep, if you have no visible leaks at the master cylinder, you probably need the zero lose brake booster spoken of in the link Plowhand gave you. Also make sure the rear brakes are adjusted up nice and tight. that could be causing the low pedal but the dropping is most likely "normal" but can be fixed with that booster.