I can tell u that maybe 1/3 of the diffs I do has the caps cut in the Center of the circle. I have been doing diffs for 40 years. The proper tools are by far the best and the fastest to use. The old school way was to install the pinion with the factory shim and see what kind of a pattern u got. Then u guessed what shim u would need. When I first started doing diffs I could not beg, borrow or steal the arbour set up. Kim
