Hi all,
I have a 96 F-350 with power stroke engine. Has a vacuum pump and vacuum brake booster. My pedal will be firm at the top and then sink to the floor when pressing. When the truck is not running or when the vacuum is disconnected from the booster I have a solid pedal. I've replaced the master cylinder three times, replaced the booster with the special zero loss ford booster, bleed the system several times, made sure the rear drums were adjusted and all hardware was in its place and bypassed the rear abs. Still have a sinking pedal and any information on something I could be missing would be greatly appreciated.

 

Where'd you get your parts from? Have you checked the vacuum pump separate from the actual break booster? How fast does the pedal seem to drop? No leaks in system or rubber lines stretching? These OBS fords seem to have problems with crappy pedal feel.

 

That's good you got the zero loss brake booster. If your vacuum pump is good, I would try gravity bleeding your brakes. It sounds like you still have air in there. Did you bench bleed the MC before putting it in? On gravity bleeding, just open the bleed valve and let some air out until solid fluid comes out, then close. Tap with a hammer and repeat. I'll do it several times, even the next day. Its a slow process but works for me.

 

Well do not feel like the lone ranger I am having issues with my 1996 dually 7.3 L after some time tuck it to Ford and they replaced the flow control valve for the brake system located on the frame worked great until I was towing a trailer and had to use the brakes real hard then the problems started showing up again. had worked and replaced everything and the valve control was the last will need to replace it again looking for one that is a heavy duty design for big trucks F350 and bigger hope this helps seem like there are some that are having a problem with this and others that have never had a problem at all.