There are three main categories of axle differentials: open differentials, limited-slip differentials, and locking differentials. They are all terms we have heard before while cruising the web forums or reading our favorite Jp Magazine issues cover to cover. In general, a differential is the mechanism that splits the power to the left and right tires at either the front or rear of the vehicle. It allows the wheels to travel at different speeds when cornering, since the tire on the outside of the turn must travel a longer distance than the tire on the inside of the turn. Most differentials from the factory come with an open-differential configuration. With this setup, the power is routed to the tire that has the least amount of traction, which can tend to be a problem when exploring off-road in certain terrain and conditions.
Locking differentials are on the other side of the spectrum. Automatic lockers can be a full differential replacement unit, like a Detroit locker. Or a lunch box–style locker that replaces the spider gears inside of the factory differential case. They both function the same in that when power is being applied to the differential, it will equally split the power to both tires. This will force both tires to power the Jeep in any situation, such as turning the tire that has traction when the other tire is slipping in the mud. Lockers also force the tires to rotate at an equal rate when cornering. This can cause the tires to “chirp” when making a turn on the pavement, reduce turning radius, and result in some overall quirky road manners. While off-road traction is increased, street driving manners are sacrificed.
My friend Sammy had a factory Dana 44 limited slip that had been rusting and collecting dust for longer than he could remember. He graciously donated the factory Trac-Lok to our cause, mainly so he could quit tripping over it. These old units can be had for cheap, if not free, as they are generally overlooked. Most Jeep models had optional limited slips from the factory, so it is possible there is already one in the rear axle of your Jeep.
There is some middle ground though in the form of a limited-slip differential. A limited-slip differential has typical spider gears found in open differentials. However, clutch discs are added to the side gears to create some friction bias to transfer power to the tire that has the most traction. By no means does a limited slip perform like a locker, and beware of manufacturers that refer to limited slips as lockers. In heavy off-road terrain and rockcrawling, a limited slip will leave much to be desired. Limited slips are excellent for wet, slippery, sloppy, or snowy terrain, especially basic mountain roads and Forest Service roads. They provide additional traction over an open differential while maintaining very friendly street manners.
There are several different styles of limited slips available through the aftermarket, and some are priced similarly to many of the full lockers on the market. Like most folks, we need to do this whole Jeep thing on a budget. Luckily, many limited slips were offered in Jeeps, trucks, and other SUVs from the factory. The clutch discs do wear out after a while and require some servicing to be brought back to their full original function. Follow along as we freshen up one of these factory limited slips and show you how to bring them back to life and working like new.
After a good degreasing and cleanup with a wire wheel, this is our starting point with this factory Dana Spicer Trac-Lok. They provide more traction than a standard open differential, but have very tame road manners compared to a locking differential. These limited-slip units are perfect for the daily driver that sees some mild to moderate trails.
The first step to rebuilding this Trac-Lok was removing the retaining clips (or sometimes a roll pin) that hold the large cross pin in place. Then the cross pin should easily slide out. It may require a light tap from a hammer and drift, but don’t get too aggressive. The original clutch packs are likely worn out, which makes it easy to rotate the spider gears around until they can be plucked out.
Once the small spider gears and thrust washers have been removed, the larger side gears with the clutches can be taken out of the case. One of the clutch packs has been laid out here in the order they were removed from the side gear. It’s pretty simple actually—washer against the gear, and then alternate clutch plates with and without wings. The retainers keep the wings all lined up and fixed to the case, creating stabilized friction in the pack.
New genuine Spicer clutch packs for a Dana 44 Trac-Lok, part number 708203, were sourced from Amazon. Be sure to source the right part number for your application. While we spent a little more time cleaning up the gears and the inside of the Trac-Lok case, we let the new clutches soak in fresh limited-slip friction modifier for a few hours, per the instructions. A 4-ounce bottle of Mopar limited-slip additive was also sourced from Amazon.
The new clutches were assembled onto the side gears in the same order the originals were removed. The new retainer clips that came with the kit were added as well. Be sure that all of the clutches are fully set down on the splines of the side gears. The gears will not set correctly into the differential case otherwise.
It takes a little finesse to wiggle the side gear and clutch assemblies into the case. The spider gears and thrust washers were lathered with copious amounts of gear oil to help them slide into place.
It quickly became apparent that the new clutch packs were exponentially tighter than the worn-out units that were disassembled. The new set was not going in without a fight. We needed to bring in the reinforcements. In this case, a piece of all-thread, some washers, and a couple of nuts were necessary to get the job done.
The hardware was used to compress the clutches into the case so that the spider gears could then set deep enough into the side gears to allow enough clearance for the spider gears and thrust washers to be worked into the case. This poses a problem in that by compressing the clutches to make room, enough force was put on the clutches that we were unable to move the side gears to rotate the spider gears into place.
A bolt was added through one of the ring gear boltholes to act as a leverage point. The compression hardware went through many cycles of being loosened and tightened. Each time wiggling the spider gears a little further into place. This is a slow process that requires patience. Take your time and don’t force it. We found it best to set the thrust washers mostly into the case and rotate the gears into place on top of the thrust washers.
An axleshaft was crimped into the bench vise and used to hold the differential side gear while a prybar was used to turn the case and gears into place, a little at a time. Once the spider gears were fully into place, the cross pin pierced them all together, finished off with the retaining clips.
This rebuilt Trac-Lok is back together and ready for duty. Be sure to add the rest of the limited-slip additive to the differential once it is time to add the gear lube into the pumpkin. That is cheap traction at its finest, from start to finish. Sometimes the best parts on the market are the ones that fit your budget. In this case, we improved the capabilities of our Jeep for about $100 in parts and a couple of evenings in the garage.
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