If you have to drive your 4x4 daily, a limited-slip differential may be just the ticket for enhancing your vehicle's off-highway capability while retaining its pleasing day-to-day driveability. A limited-slip that offers the best of both worlds is Eaton's new Carbon limited-slip differential.
This torque-sensing unit features a high-strength case designed to withstand a significant amount of abuse. This goes for the precision-forged gears as well, which are designed to mesh perfectly, providing improved strength and durability over the standard-cut gear. The race-bred pyrolytic carbon friction discs located behind each side gear are pre-loaded by a central spring assembly, increasing the clamp load on the carbon discs as input torque increases. This balanced design ensures that the bias torque of the differential is proportional to the input torque, which should result in smoother engagement. The revolutionary carbon discs are made from patented high-temperature carbon-fiber and wrapped in a carbon anti-wear coating. As a bonus, Eaton says these virtually indestructible discs maintain their lubricity to provide smooth, quiet operation over the life of the vehicle.
We installed Eaton's Carbon limited-slip differential in the rear axle of one of our workhorse four-bys, a '95 Chevy K2500. Matt Dinelli at Attitude Performance in Arlington Heights, Illinois completed the install in a little over an hour. To date, we're very pleased with the Carbon limited-slip's silent and seamless operation. One of the primary benefits of this unit is the fact that it provides enhanced mobility by transferring up to 50 percent of power between the two rear wheels, where traditional limited-slips provide between 25 and 40 percent.
Eaton offers the Carbon limited-slip differential for a slew of applications, including 10-, 12- and 14-bolt GM, Ford 8.8- and 9.75-inch and Kia Sportage, Hyundai Santa Fe and Mitsubishi Montero Sport axles. Following are the basics of an install in a '95 Chevy K2500 dualie equipped with a 14-bolt full-float rear axle.
Understanding Backlash
Because we reused the original ring-and-pinion in our Chevy, the only critical dimension we had to be concerned with was backlash. Backlash is the amount of space between the meshing teeth of the gears, and it's needed to allow for heat expansion. As gears operate, they produce friction and heat. This makes the gears expand, reducing the clearance between the meshing teeth of the gears.
Without backlash, the ring-and-pinion teeth can jam into each other and fail very quickly. However, too much ring-and-pinion backlash can cause gear noise. Before we removed the stock differential from our 14-bolt axle, we positioned a dial indicator stem on one of the ring-gear teeth. While holding the pinion gear stationary, we wiggled the ring gear back and forth. The indicator needle movement measured backlash, and we noted this dimension. When installing the new limited-slip, we once again used the dial indicator to set the backlash to within 0.002 (plus or minus) of the original setting.
To increase backlash, move the ring gear away from the pinion gear. To decrease backlash, move the ring gear towards the pinion gear. On the GM 14-bolt axle, this movement is accomplished by simply turning the adjusters that are located on either side of the carrier. U-shaped retainers lock the adjusters in place when the proper measurement is reached. Other axle applications require moving shims from one side to the other until the proper measurement is acquired.
 00: This is a cutaway of the...  00: This is a cutaway of the Eaton Carbon limited-slip unit. Here you can see the high-strength case that houses the precision-forged gears and other internals. Behind each side gear are the carbon-fiber discs that are wrapped in a carbon anti-wear coating. |  1: To begin the install, raise...  1: To begin the install, raise the rear axle wheels and place the transmission in Neutral. Remove the differential cover to drain the oil and then remove all of the old gasket material from the mating surfaces. |  2: Remove the eight axleshaft...  2: Remove the eight axleshaft retaining bolts and pull the axleshafts out several inches to keep them from impeding the removal of the differential assembly. |
 3: Using a dial indicator,...  3: Using a dial indicator, measure and record the ring-and-pinion gear backlash. Then remove the differential side bearing caps and the retainer that holds the adjusters for preload and backlash. Loosening the adjusters will allow you to remove the carrier. Make sure you mark the bearing caps so they can be re-installed exactly as they were. |  4: Remove the ring-gear bolts...  4: Remove the ring-gear bolts and then use a press or hammer and drift punch to remove the ring gear from the differential. |  5: Use a puller to remove...  5: Use a puller to remove the carrier bearings from the stock differential. If your rig is older, it's wise to replace both bearings with new ones. |
 6: After ensuring that the...  6: After ensuring that the mounting surfaces are clean, install the ring gear on to the new Carbon limited-slip differential. It can either be pressed on using a hydraulic press or by equally and alternately tightening the ring-gear bolts. |  7: Using a hydraulic press,...  7: Using a hydraulic press, install the carrier bearings onto the new differential. |  8: Firmly seat the new differential...  8: Firmly seat the new differential assembly into the axlehousing and re-install the right and left differential side-bearing caps. Tighten the bolts to the recommended torque specification. |
 9: Use a dial indicator to...  9: Use a dial indicator to check the ring-and-pinion gear backlash. Make backlash adjustments by turning the adjuster. In some cases it may be necessary to slightly loosen the bearing caps to facilitate turning the adjusters. |  10: Once the backlash is set,...  10: Once the backlash is set, re-install the retainer that locks the adjuster in place. |  11: After applying a bead...  11: After applying a bead of silicone between the mating surfaces, re-install the axleshafts and tighten the eight bolts at the ends of each shaft. |
 12: Reinstall the differential...  12: Reinstall the differential cover with a new gasket or sealer and tighten the cover bolts to proper torque specifications. |  13: Remove the lubricant fill...  13: Remove the lubricant fill plug and fill the differential with the recommended volume and type of axle-gear lubricant and limited-slip differential additive. Re-install and securely tighten the fill plug and testdrive the vehicle to ensure proper installation. | |