Swappin' Gears

A 12-bolt behind an overdrive gets some low-end punch

The quest for all-around performance can be accomplished in a variety of ways. The owner of this particular vehicle initially chose a Gear Vendors overdrive unit that literally gave him six forward speeds. It worked great, but he then decided that he'd like a bit more punch off the line and in in-town driving. To accomplish this he dropped the truck off at the Diff Works in Riverside, California, for a gear change and Posi upgrade. The truck was originally equipped with a 3.07:1 ratio, but the owner chose to install 3.78s for that little extra low-end punch. I happened to be in the right place at the right time so I was able to chronicle the swap and show you how the professionals perform a rearend upgrade with a small pile of high-quality aftermarket performance parts. Check it out.

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Gary Maib of Diff Works in Riverside, California, was kind enough to let us look over his shoulder while he completed the gear and axle change. The first step is to pop the cover and drain the gear lube.

Once drained he scraped off the remainder of the gasket and cleaned the gasket surface of the housing.

This particular vehicle is equipped with rear discs. In order to pull the axles, the calipers and rotors will have to be removed. On drum-equipped vehicles the drums and backing plate assemblies will have to be removed, as well.

GM rear axles are held in place with C-clips. The OEM differential uses a pin that slides between the two axle ends, which exerts a bit of outward pressure on the axles thus holding the C-clips in place. The pin itself is held in place with a locking bolt that must be removed before the pin will come out.

Gary uses a magnet to snare and remove the C-clip axle retainers. Once both are removed the axles can be slid out of the housing.

If the axles were to be re-used they could just be pulled out, as shown, and left sitting in the housing while the work takes place--since he'll be replacing the OEM axles for a pair of Yukon items they were fully removed from the housing and set aside.

After removing the bearing caps (pay attention as they're distinctive left- and right-hand items) the differential is coaxed out of its nest. It often takes a bit of muscle to get the differential to "pop" though I've seen some virtually fall out, as well.

Once the differential is out of the housing you can then remove the pinion yoke and then the shaft.

Like the differential, the pinion often needs a bit of coaxing to come loose.

With the guts removed the next step is to drive out the pinion bearing races. Using a punch, and a fair amount of finesse, drive the forward race out the front and the rear race out the back.

Now that you've got an empty housing, it's time to give it a good cleaning. This not only removes residue from the original gear lube but washes out any foreign matter, as well.

A neat trick for installing the new pinion races--the front one, at least--is to use the old one to drive in and seat the new one. The rear, or inner race, can be installed using the punch used to drive out the old one--again, use some finesse.

For maximum performance, Gary chose a Truetrac Posi differential and a Yukon ring-and-pinion set. The ring gear is prepped for attachment to the differential by scuffing the mating surface with 80-grit emery cloth to remove any rust preventative or burrs that'd interfere with a perfect mating with the differential.

The ring gear is then attached to the Truetrac. The bolts are treated to an application of thread locking compound and then torqued to specification.

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