If looking to enhance overall driving experience with amplified wheel traction and handling, then installing this helical-gear style Eaton posi/limited-slip unit may be right up your alley. A GearHead4Life (AG4L) YouTube user installs a Eaton Detroit Truetrac posi/limited-slip onto his LS-powered 1987 Chevy C10 truck. Like all videos that we share in our articles, we thought this one would be useful for anyone looking to take on such a project themselves.
On the table to start, he has 3 quarts of GL-5 oil ($18), differential x2 and x2 race bearings ($45), and Richmond shim kit ($19), and last but not least, the Eaton Detroit Truetrac Posi/Limited-slip differential 10-bolt 8.5″ 28-spline axle (part #912A556 shipped from Summit on eBay for $385). All parts needed including the diff unit totals out to $467. Be sure to have your torque wrench and sockets available because you’re going to need them. This 10-bolt diff unit doesn’t use clutches, just gears inside to make it function.
First, take the diff cover off of your current unit and drain all oil. Once both are complete, rotate until you reach the cross pin point. A 5/16th socket was used in the video to remove the cross pin bolt. Also, go ahead and take out that cross pin. Normally these cross pins slip right out, but since this C10 truck was using a welded “Lincoln locker,” it held more resistance than usual. Next, remove the carrier cross pin.
To remove the C-clips easier, remove the rear wheels and brake drums to push axles. Pull the axles out about 10″ to get them out of the carrier. He then removes the 4 bearing cap bolts as well as the left and right bearing caps. After that is all done, it’s time to say goodbye to the old unit and clean out any old gear oil.
Install the carrier bearings on the new diff and make sure that you press the bearing on by the center piece and not on the bearing itself as you do not want to damage the bearings or the cage. Make sure it sits flat with no gap. Now install the ring gear on the Eaton diff, and make sure it’s a tight fit. Line up the holds and put in the reverse-thread bolts and use a 3/4″ socket to tighten. Tighten until the ring is up and seated against the differential and torque the ring gear bolts (reverse thread) down to 65 ft-lbs.
Now it’s time to put install it on the truck. The factory shims won’t normally fit an aftermarket differential, that’s why it’s crucial to buy the adjustable aftermarket shim kit. Also, backlash should be .005-.009 on the dial indicator. With the side bearing caps bolts torque to 60 ft. lbs.
It’s wise to check the gear pattern. He is using 3.42 gears from a ’94 Chevy truck. In this video, he puts white grease on 1/3 of the gear teeth. He puts resistance on the gear and rotates the driveshaft against him to see how the pattern measures up. You want to make sure this pattern is more centered (where the grease has been cleared).
Now it’s time to put the C-clips back on and then put the Eaton lock in the diff to hold the axles in place, then put the plug that was provided with the differential unit in and make sure it is seated all the way around. After that, make sure you use about 2-1/2 quarts of oil to lube it up, then slap the cover back on with some RTV gasket maker to prevent any leaking. After installing it back in and throwing the brake drums and wheels back on, you should be good to go!
Amie became a fan of fine machinery as a kid thanks to her dad; a pilot and professional skydiver, and was always there to help tinker around on Cessnas and old Chevys. Amie has been writing in the automotive field for years on all makes and models.
