I rebuilt the rear brakes on my 1987 F250. Shoes and wheel cylinders and still the rear brakes get hot. I was told it will be the
proportional valve or master cylinder. Can the porportional valve be fixed or just have to be replaced?

 

That valve will control how much pressure is sent to the brakes when you press the pedal. If it is clogged and you aren't getting much fluid movement, could be an issue.

My drum brakes in the rear have an adjuster for a situation like this. It is supposed to self adjust but if it isn't, the brakes can rub. Maybe look for that. With mine, there is a dust cover to remove and you can manually adjust with a screw driver.

Other reason for heat...bad bearings in the area?

 

Another possibility is the rubber flex line. Those can sometimes fail internally and hold pressure to the brakes...

 

Right now I'm going to change the master cylinder. I talked to a mechanic I know and he said after I described the problem it was the master cylinder or the proportioning valve. After I found what Ford wanted for the porportioning valve I went with the master cylinder since I already had one. $285 for the proportioning valve and a dealer item? REALLY? Found the local junk yard hade one for $35.00 but I had to bring mine in to compare it to.

 

Changed the master cylinder and still had the same problem. Found a proporting valve and no more problem. BTW, it came off of a F150