Setting up the proper tooth contact pattern and backlash is an absolutely essential part of ring and pinion gear installation, and there's only one chance to get it right. The gear teeth are lapped together during manufacture, and they must be set up in that exact relationship as they're installed. Wrong assembly will result in short gear life and/or noise.

New pinion and carrier bearings, seals, and small parts should be installed along with the gears for the best results. A properly set up gearset should outlast several engines, transmissions, and body parts. Rear ends are some of the longest-lasting parts on any vehicle.
Jerry

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