Hello,
At work we have a 96 F350 dually dump body. The rear drum brakes have been giving use problems. Last week they were locking up aand the brake light would come on. Got it back to the shop and took the drums off and on the passenger side, the retention springs and pins were off. In fact, the pins were missing and one spring was ground to just about nothing and the other one was worn down a little to. Replaced the missing hardware (drums and pads were good yet amazingly) and adjusted both sides since they were way out of adjustment.
I also replaced both emergency brake cables since they were starting to seize up as well. Tested the truck and they seemed good. We used it Wed, Thursday and Friday(today). Wednesday, it was fine, brakes worked great. Then Thursday the brakes would start to lock up again, but not as bad this time. It doesn't do it all the time either, but only does it (that I noticed) when pulling out from a complete stop. Brake light comes on once in a while, not all the time like the last time.
To me it seems like the wheel cylinders are not functioning properly and allowing the fluid back. Told my boss this and he said they were supposedly replaced by the last guy who did a brake job on it (outside person) I did not wash them down with brake cleaner like I usually do cause we were out and Napa was out to. They did not appear to be leaking, but they also did not look new.

I will be working on this tomorrow again, and was wondering if there is something I should be looking at besides the wheel cylinders. Its been a long time since I dealt with drum brakes.