[Jeff Chambers]

Pinion will be sucked into the meshed on the drive side and pushed out of the mesh on the coast side. This is due to the hypoid shape of the gears. If you can see the pinion moving fore and aft, you've got problems. The pinion nut should be torqued until there is approximately 18 to 24 in-oz running torque on new bearings or 10-15 in-oz on used bearings. The pinion will not move fore/aft if the bearings are properly preloaded. Basically, the pinion has opposed angular roller bearings that are preloaded against each other via the crush sleeve/pinion nut stack up. For a 8.8", this is about 0.008" of total bearing preload, or 0.008" past zero lash. This is the pinion zero lash point, not the zero last point of a new, unused crush sleeve. The bearing have to be properly preloaded to carry the axial loads from the hypoid gear mesh properly.

You shouldn't use an air gun to preload the bearings...the control just isn't there. It'll take less than 1/4 turn (on average) to get to proper preload after reaching the zero lash point. You need to be using a breaker bar and sneaking up on the preload about a 1/16th turn at a time. Too much preload and you'll burn bearings, too little and you'll ruin the gears.