Brakeless, Thanks for your question on Just Answer. There is a pretty common problem that is over looked or forgotten about. Check the Dump valve, mounted on the frame on drivers floor board. I am attaching the TSB that deals with this. To test and verify that this is the problem you can use a piece of brake line and bypass the unit. Good Luck and if I can be of further assistance please let me know. Keith
90ford24WAGNER BRAKE CENTER
Bulletin No. 24
Date November, 1989
Note that brake fluid over a period of time absorbs contaminants, therefore, annual flushing and replacement with clean, fresh brake fluid will help to prevent this condition from occurring.