I have a 88 f250, 7.3 engine. I'm having a brake problem. When the engine it running and the brake pedal is depressed it will go all the way to the floor. I have no leaks and the master cyl. was replaced to no avail.
can any body give me a clue as how to fix this problem

 

You have air in brake system.
Is the system leaking fluid. Is there moisture in the fluid.
Start at rear and bleed brakes carefully. Put a small hose on end of bleeder and into fluid container. Keep master cylinder full of fluid.
You should do this when truck is running. Seems to help me get a firmer pedal.
After you are sure There is no air in rear then go to front.
Try bleeding them again and let us know how it turns out.

 

I usually have to go back and bleed it a couple more times. Especially since you introduced air into the system all the way at the MC so the bubbles have a long way to go.