Electrical help please
I don't believe there is any adjustment and they don't wear out unless they are dragging. I would pull it apart and clean/inspect everything parts are cheap and easy to find. They used that brake on about every school bus and garbage truck out there. The cable from the air cylinder to the brake is often the culprit. Good to have it working properly as its your backup is you loose all air pressure.
My 94 needs some attention too. I always block a tire just out of habit.