On my 99 e-250 I just replaced the master cylinder to try and get rid of brake drag. It did help a lot but sometimes lighter but similar symptoms return usually after being driven thru town and back home. I am suspecting the valve that is located on the rear port of the master, a 1"1/2 long metal thing that screws into the large hole on the MC that you then connect your rear brake line to. Is this the proportioning valve? or what is it? I have disarmed completely the rear ABS unplugged the computer and removed the ABS valve etc and ran my rear brake line directly from the rear master port. Ford of course wants $52 for this little monkey, what a surprise HUH? Anybody know where I might get a better deal?