Since our pinion was being reused in the same case, we didn't change thepinion shim, which sets the pinion depth, a critical spec for propergear mesh. The shims slip between the pinion gear and the bearing beforethe bearing is pressed on. Required pinion depth is easily checked, butonly if the elaborate set of special tools required is on hand. Withoutthese tools, some trial and error is needed. It's best to just set upthe gears with the same shim that came out and then check thegear-contact pattern after the rear is assembled. The contact patternwill reveal if the pinion depth is off and needs adjustment.