Pull the axleshaft and pry out the carrier and ring-and-pinion. We retained our carrier's bearings, since our Xterra had just 15,000 miles on it. The lip of the diff housing where the pinion seal fits must line up exactly when you're done. Here, our mechanic measures the preload on the gears at 5 in-lb. Since we're keeping our original bearings, this was the rating we'd work toward with the new ring-and-pinion. With new bearings, we'd set preload somewhat higher, probably at about 10 in-lb.