I have a 95 ford f150 which has a serious brake problem. I can drive about ten to twenty miles and the back brakes start to lock up, I pull over and open up the furtherst bleeding valve, and can drive again. I have had replaced the master cyclinder, wheel cyclinders, rubber hose going from frame to rear axle, drums, rear brakes, front pads, front calipers, had the system drained and refilled. This truck just loves the mechanic shop. His only answer is to replace booster, or maybe the portioning valve. I am sick of just replacing things on this truck. Has anyone ever heard of the problem? Also the abs switch has been replaced. Thanks Steve

 

Sounds like a proportioning valve sticking.

 

You have a truck with rear ABS. Those are symptoms of rear Proportioning valve.

 

notice the last post was 10 years ago man?

 

Just joined yesterday due to having a brake situation and didn't notice year of post. Getting old like my truck,,,