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Limit Your Slip

Posted in How To on January 23, 2004
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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.

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Attitude Performance
Arlington Heights, IL
Eaton Automotive, Torque Control Products Division
Marshall, Mi 49068

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