Hello all: We have a very well used Cat Thirty that will not stop despite the large adjusting nuts threaded as far as they will go. The lining feels like it is 3/16-1/4' thick on the top of the drum and looks like it still has some meat left at least on top. Is there another keyway in the operating lever (Brake cam) or in the operating lever shaft? Could the lining be worn out on the bottom where I can't see it?  Any  thoughts would be greatly appreciated!