Technical Having trouble getting drum brakes working right

5/16" measured at that point is a huge amount of clearance. Most seem to to less that 1/8" IME. With the normal 6-7 to 1 leverage that translates to around a full 1" pedal travel.

As others mentioned, be sure the return port is open and you should be good.

 

Right, and that seems to have been where I screwed up. The actual clearance was much about a paperclip but it took about 3/16s of adjustment to solve the problem. I have been driving it for a couple of weeks now and all is well. The brakes do not drag, and I can stop easily. I already had a pedal return spring, but that is a good suggestion.