After I thought I had the gearbox input cup's setscrew tightened, I realized setscrew wasn't seated on flat spot on diff pinion gear. Why? Because everytime I would push the CVD/input cup onto the pinion, the gear would move into the gearbox... not enough of the flat spot to tighten down setscrew. I was stumped for a moment, and had contemplated tearing gearbox apart to get to pinion gear. Hook and pick set, that I use mainly for pulling bearings, was used to pull the pinion gear out of gearbox, and into position.
