I've got a 83 z28 that makes a rotational knocking/thumping noise when brake moderately hard. I've changed the lug nuts, and cleaned the wheels mounting surface. It seems to be coming from the right rear corner. Just pulled the rear drums off looking for anything obvious and have come up with nothing. I dont see any wear marks from anything hitting. Anyone ever encounter this? And help would be great. The noise scares the crap out of me and I have no idea. Gonna throw new shoes on it and see what happens but im doubting thats my problem...