I believe my brake lines were restrictive, perhaps collapsed inside the brake hose between frame and differential, and causing the brake to be partially engaged and not fully releasing, which lead to heat build up and cylinder failure. The cylinder was leaking. After replacing the cylinder and brake shoes last weekend I got back home. On the way home I stopped often. One time I stopped in the middle of the trip the wheel was normal outside temperature. The other times I stopped I thought the wheel was excessive in temperature, as in uncomfortable to hold the hub cap for more than 5 seconds. So the problem was intermittent.
This weekend I replaced the brake lines from the front to the back including hose, tee, and lines going to the cylinders. Bleeding was a whole new story compared to last weekend, about 10 pumps of the brake filled the little bottle on the one-man bleeder tool. Much more volume and free flowing this time. Preliminary test drives do not heat it up. I’m going to monitor it for the next 20 or 30 trips and see how it goes.
If this fix sticks it is the same thing as posted by Knanthrup in this old thread
http://67-72chevytrucks.com/vboard/s...d.php?t=609667