Jeep Wrangler TJ: G2 Gears, Detroit Truetrac, M.I.T. Drivetrain Work [Video]

Dec. 07, 2011 By Josh Burns, Video by Adam Wood and Josh Burns
We turned to M.I.T. Drivetrain Specialists in El Cajon, California, to help us repair our axles and install our new G2 gears and Detroit Truetrac limited-slip differential.

Hoping to get our Jeep Wrangler ready for the trails, we moved on to the next step in our TJ build. Our journey began when we purchased a used 2000 TJ Wrangler we found on Craigslist. We wanted to build a trail-ready TJ in stages without completely breaking the bank. For now it would be a great adventure vehicle for weekend fun, leaving open the possibility for something more hard-core in the future.

In our first story for the build, we headed to Off-Road Warehouse’s Temecula shop to help us replace the TJ’s suspension components with a 4-inch Skyjacker lift (TJ401K-SVK-H) as well as replace the upper control arms. We also replaced the tires with new BFGoodrich 33-inch Mud Terrain KM2s which we installed on the new ATX Wheels Slot 15x7 wheel.

Our 2000 Wrangler is put on the lift to begin the front and rear axle work.

When we purchased the Wrangler it only had about 50,000 miles on the motor (great since it was a 2000), but it did have a salvage on the title from a front-end collision years ago. After the Skyjacker kit was installed, it was clear the front axle was a bit out of whack. While we wanted to move up from the 3.73 stock gearing to compliment the larger 33-inch tires, we also had an important decision to make – replace the axles, upgrade to a larger axle, or repair the existing axle.

The stock TJ comes with a Dana 30 front axle and a Dana 35 in the rear. Although moving up to a Dana 44 or larger would increase the vehicle’s off-road durability, the change comes at a cost we aren’t yet ready to incur. Replacing the axles finding used housings of the same size was an option that might not cost a fortune, as we found some on Craiglist and also at local wrecking yards. The only problem is the uncertainty of the axle since it’s hard to tell exactly what has happened to it during its lifespan, or even how many miles are truly on it.

An entire wall in the 10,000-square-foot M.I.T. shop stores a variety of different axle housing of all shapes and sizes.

After some research we came across a shop in San Diego County called M.I.T., an acronym for Mechanically Inclined Technicians. The shop, which goes by the moniker of “Driveline Specialists,” is owned by longtime off-roader Jeffrey Sugg. The company could not only perform the work on installing new G2 gears and Eaton’s Detroit Truetrac Differentials, but they could also repair our bent front axle. If repairable, the axle joint would need to be welded and resealed – something the shop could handle in house or send that day to a nearby welder.

Ring and pinions of numerous ratios line an entire wall in the shop of M.I.T.

M.I.T. offered a realistic option for all of our needs. They could assess the front axle and repair it (or even offer a replacement if need be), and as opposed to just finding another axle we would know for certain that the repaired stock axle would be sound.

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We headed down to M.I.T.’s shop in El Cajon, California. The company has been in business since Sugg first started it back in 1989. A few years later he married wife Karen, and the two mange the business today (he the shop, she the finances) out of its nearly 10,000-sqaure-foot facility that features 10 working bays. The shop has six technician busy spinning wrenches, while Kenny Thomas and Cathy Martin help man the counter and phone lines in the showroom.

“We do a lot of work on custom vehicles, hot rods, off-road… it pretty much runs the range. Anything with axles and transmissions in it we’ll work on,” Sugg said, noting they even work on a number of commercial vehicles but the core is mostly enthusiasts. “You will always tend to see more off-road material in here than anything else.”

Yeah, there may be a Mario Lopez that can dance, but I bet you he can’t install new gears! M.I.T.’s Lopez drains the gear oil from the rear axle of our TJ.

Sugg actually created the first slip-yoke eliminator kit for the NP231 and NP207, but he lacked the financial backing to battle for the patent on the design. His Jeep and drivetrain knowledge runs deep, which explains why even his shop technicians still run some of the work by him to see if he can catch anything they might’ve missed. Although the shop, which has been in the same location but has expanded a number of times over the years, focuses on driveline work, it does also tackle a number of other jobs.

Other Jeep Wrangler TJ Stoies:
Skyjacker Suspension, BFGoodrich Tires and ATX Wheels

Bestop Supertop NX Softtop
“Our core business is drivetrain, is gear systems, but we also do suspensions, we do a lot of custom work, and we also do engine conversion work, so pretty much anything to do with the drivetrain area we will handle,” Sugg said. “We do custom axles, we repair stock axles, we straighten them, we modify them, we’ll do transmission transfer case conversions, driveshaft upgrades.”

After the axle has fully drained, the gears and differential can be removed.

M.I.T. is clearly the right shop for our needs. The stock gears in our 2000 Jeep Wrangler feature a ratio of 3.73, which just wasn’t cutting it when we moved from 31-inch tires up to 33-inch BFGoodrich KM2s. After speaking with Jeepers with similar setups and Mark Mathews at G2 Axle and Gear, we decided upon a 4.56 ring and pinion for our TJ. G2’s gear set would help get our Wrangler up to speed, literally. Since our diff covers were a little dinged up, we also opted to replace them with G2’s differential covers, which are constructed from lightweight aluminum to help dissipate heat while its added reinforcement ribs provide rigidity and strength. We also didn’t want to skimp on the oil we used, so we opted to try Royal Purple’s synthetic gear oil to bath our new gears.

New Eaton Detroit Truetrac gear-driven, limited-slip differentials will be installed in both the front and rear axle to provide improved traction on the trail.

When it came to our differentials, we turned to Eaton’s line of Detroit Truetrac differentials. Hailed as the first helical gear differential ever introduced to the automotive aftermarket, this limited-slip differential fit our needs well. Rock crawlers would opt for an air locker or something more hard-core, but the Detroit Truetrac would provide significantly improved traction over our stock differential without requiring a more costly locker setup and regular maintenance.

Eaton's Detroit Truetrac is a gear-driven limited-slip differntial that remains open until a loss of traction occurs.

The gear-driven limited-slip Truetrac (shown above) is designed to remain open until traction is needed on the trail, essentially providing torque to the wheel with the best footing. For our all-around trail use, the Detroit Truetrac compliments our setup and intended use.

Moises Prado removes all of the suspension components to remove the front axle.

The stock pinion is removed after the differential housing is gutted.

Helping us with the install was Mario Lopez and Moises Prado, two very skilled technicians who have performed their fare share of axle and gear work. While Lopez went to work on the rear axle, Prado worked on disconnecting the front and removing the stock gears. The big surprise of the day came when Lopez shoved an alignment rod through the rear axle to only hear it thud and not come out the other side. “That’s not the sound you want to hear,” he told me. Not only was the front axle bent, but the rear one as well. Lopez said this happens more often than you’d think, but it certainly caught us off guard. At least we were at the right shop to fix it.

To get all the dirt and crud off the axle before straightening and before it eventually gets welded, M.I.T. uses a parts washer to help get the dirt and grime off the axle.

M.I.T. offers axle straightening at its shop in El Cajon, California. As noted from the progression from the top image to the bottom, the axle housing is literally bent back into shape. M.I.T. does have its trade secrets as to how the entire process works, but it helped get both our front and rear axles back in shape.

Fortunately the rear axle’s bend wasn’t too bad, and the larger Dana 35 was not a difficult repair – just unexpected. The Dana 30, on the other hand, was repairable but is a much trickier fix, since the smaller housing has less material to work with. Prado was able to work his magic on the custom axle-bending setup that Sugg built for this very purpose. Without giving away his trade secrets, it’s a very effective way to repair bent axles, and the alignment rod will ultimately tell the story of whether the axle is back to being straight.

The alignment rod seen in the center of the axle housing shows the axle is straight again. It now will push through one end of the axle to the other – something it wouldn’t do when it was first pulled off the TJ.

M.I.T. proved to be a great resource for us. Not only do they offer a number of services, they also offer a wealth of knowledge and resources. If an axle is not repairable, there’s a good chance the shop has another housing lying around. If we decided to upgrade to a larger housing in the future for more serious rock-crawling, they also can perform custom work and axle conversions.

After our break-in period, we’re looking forward to hitting the trail. We have more work to do on our TJ, but now it’s finally ready to get dirty. Stay tuned.

Moving from the stock 3.73 ratio to a lower 4.56 will help compliment our larger 33-inch tires. We used gears and new differential covers from G2. As for the differential, we replaced the stock unit with Eaton’s Detroit Truetrac limited-slip differentials.

The stock differential (right) is swapped out for a Detroit Truetrac in both the front and rear axles. The limited-slip Truetrac differential remains open until there is a loss of traction, in which case it will transfer power to the wheel with the most amount of traction.

The new G2 gears are checked for proper backlash, which is the clearance between the mating ring and pinion gear. It is literally defined by slight fractions, as the tolerance for these gears should be between .07 and .10.

The gears are installed in place to check fit and function. A compound grease is applied to the gears and then the gears are manually driven to see if they line up properly.

Looking at the grease on the ring gear, it’s clear the pinion gear is making contact with the ring gear in the center of the teeth – right where it should be.

The Dana 30 front axle was welded and resealed after being straightened earlier in the day.

The axles are given a quick coat of paint to give them a fresh look before being reinstalled.

The rear axle is aligned and installed, as the suspension components are reattached as well as the driveline.

The C-clip is installed in the Detroit Truetrac differential in the rear.

With the surface fully cleaned off all debris, silicone is applied to the differential cover location.

The differential cover is put in place, with the bolts placed on only finger tight. After about 15 minutes of drying time, the cover gets bolted on.

New gears require a break-in period that must be followed to insure their life and proper function. The rear differential oil will need to be changed in the first 300 to 500 miles. Although we will have to swap out the oil very soon, we used Royal Purple’s synthetic gear oil. Although it is more expensive that standard gear oil, Royal Purple says its gear oil is designed to reduce friction to thereby keep temperatures down during the break-in period, which we felt was worth the extra coin.

While installing the front axle, Moises and Mario noticed a badly tweaked bracket (again, a casualty of the accident the Jeep was in years ago). In the future we will simply replace the brackets, but for now M.I.T. was able to simply weld the bracket and make sure it is solid and secure.

Eaton Detroit Truetrac

G2 Axle & Gear

Mechanically Inclined Technicians (M.I.T.)

Royal Purple

ATX Wheels

BFGoodrich Tires

Off Road Warehouse

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