Or also, have you cleaned and greased the 6 contact spots on the backing plates where the brake shoes ride? They need to be cleaned and a light coat of axle grease on the 6 flat spots on the backing plates so the shoes move freely.
This is good advice, but first check to see if the backing plates don't have deep worn spot, "divots" into them, where the shoes have been for decades.
If the divots are deep, they need to be welded up, and ground smooth so the shoes can move, and then retract.
Have seen too many worn backing plates, when i was a full time wrenching, mechanic.
