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Though most of us would like to think we’re pretty handy with a wrench, our Chevys sometimes require tasks that we’d just rather pay someone else to do. Paint and body is always the most feared job, but setting up a differential is usually a close second, just ahead of installing seat covers. We’ve happily forked over two or three bills - in labor alone - to have a new ring and pinion set up by a professional. Curiosity finally got the best of us and we decided it was time to tear into the venerable 12-bolt and learn - by ourselves - what it takes to overhaul a tired unit into a strong, reliable torque twister. Our plan was to source a 12-bolt housing, axles, Posi-Traction carrier, and gear set, average swap meet fodder, and assemble them with new bearings and seals for an low-budget buildup. That’s not exactly how things went, of course, since our original axles ended up too galled to use, and our “cherry” used Posi case showed evidence of self-destruction once we opened it up. To be fair, this stuff was more than 40 years old. Fortunately, there are plenty of affordable brand spankin’ new upgrades for the 12-bolt that will help ensure many reliable years of parallel black marks on the concrete. We contacted National Drive Train for a new Eaton Posi, beefy 30-spline axles, and an installation kit consisting of bearings, shims, seals, and marking compound to check the gear pattern during the shimming process. Our swap meet original GM 3.55:1 gear set checked out fine, and our used 12-bolt housing looked good to go after repairing broken shock mounts. We had all the hard parts we needed to proceed. As you might expect, there are some special tools that make this job a lot easier, and we didn’t buy ‘em, we made ‘em ourselves. Even if you don’t have access to a machine shop like we did, you can create tools that are functionally equivalent. Strip down the housing. The brakes need to come off first, and be sure to keep all the emergency brake hardware, self-adjusters, and special parts that don’t come with a shoe kit. Pop off the inspection cover, remove the long bolt that holds the cross-pin inside the differential carrier, and slide the cross-pin out. Now you can push each axle inward, toward the center of the differential, so that the C-clips will fall out (a magnet helps retrieve them). The axles should slide out of the housing. Now remove the differential carrier, following these two steps first. Mark the carrier bearing caps so you can reinstall them on the same side. Reinstall the cross-pin and the retaining bolt in the carrier so its guts don’t eject when you remove it. Now remove the carrier from the housing. Keep in mind that the factory installed a shim on the end of each bearing race, which sets the proper backlash in the gears and preloads the bearings. Unless your bearings are completely wasted, you’ll probably have to pry the carrier out of the case to overcome the preload friction. At this point, you should be looking at the pinion gear and little else. It’s the hardest single step of disassembly but a few special tools make it pretty easy. Illustrated in the captions, the first tool is basically a long breaker bar that bolts onto the pinion yoke to keep it from turning when you’re removing or installing the pinion nut. The other tool is a yoke puller that frees the yoke from the pinion gear, as the bugger is often difficult to remove after decades of service. Remove the pinion nut and yoke with whatever tools/contraptions you can whip up, tap off the pinion seal with a hammer and punch, and then you can remove the pinion gear from the housing. Our gear expert, Freddie Byers of Byers Performance, says the outer pinion bearing often fits tightly around the pinion gear, a gross understatement in our case. Note that the backside of the pinion gear has a shallow cone-shaped divot in the center: that’s great for centering a big punch so you can apply strong blows with a hammer to remove the gear (just be sure not to screw up the threads). Be sure there’s something soft underneath it to cushion the fall of the pinion when it’s driven off the bearing. With the pinion removed, the crush sleeve should slip right off but the front bearing is an interference fit and must be pressed off later. |
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