And the drums as well. Everything is based off of the offset of the axle flange as it sits in relation to the housing. It extends out a certain amount, the drum mounts to the face of the flange, and the brakes are back set from that. So, since they are set to use an 1 3/4” shoe, and the shoes are mounted to the backing plates, a 2” shoe would be too wide, and a 2” drum would rub the backing plate. Redrilling the drums and axles is the old school way to use the existing brake setup for a large bolt pattern. Nowadays, they make up that difference in an aftermarket axle already drilled for large bolt and offset to use large bolt brakes of any configuration. Of course, Dr. Diff still sells axles in the original 1 3/4” offset that would only require redrilling your drums if he makes them with the large bolt pattern and you still want to use your existing brakes.
