Eaton 912A579 Detroit Truetrac Limited Slip Differential for 1976-09 Jeep/Hummer

Vehicle Fitment

• 1976-1986 Jeep Cherokee (Base, Chief, Laredo, Wide Track)
• 1976-1986 Jeep CJ5/CJ7 (Base, Renegade, Laredo, Golden Eagle, Limited)
• 1976-1986 Jeep Wagoneer / Grand Wagoneer (Base, Limited, Custom, Brougham)
• 1976-1986 Full-Size Jeep Trucks (J-Series / J-10) with AMC 20 Rear Axle
• 2003-2009 Hummer H2 (Base, Luxury, Adventure, Special Editions)
• 2006-2009 Hummer H3 (Base, Adventure, Luxury, Championship Series, X, Alpha)
• 2003-2004 Hummer H1 (Base)
• 2006 Hummer H1 Alpha

Fitment Notes

• Only fits vehicles equipped with an AMC Model 20 rear axle.
• Requires 29-spline axle shafts.
• Ring & pinion ratio must be **3.08 or numerically higher** (i.e. ≥ from 3.08 upward) to use this differential. 
• Does not include carrier bearings - you may need those depending on your axle condition. 

Features

• Helical-gear design provides smooth, quiet limited-slip operation. 
• Maintenance-free - no wearable friction clutch parts. 
• Automatic torque biasing under wheel slip conditions. Works in both forward & reverse. 
• Designed for heavy duty use: off-road, towing, work trucks, rock crawl, etc.
• High durability steel carrier. 
• Compatible with standard GL-5 gear oil; no friction modifiers required. 
• Optimized for high torque bias ratio for better performance in demanding applications. 
• Proven heritage design used by both aftermarket and OEM (for example on Hummer H1) applications. 

Specifications

• Part Number: 912A579
• Axle Type: AMC 20, rear axle
• Axle Shaft Spline Count: 29 splines
• Axle Shaft Diameter: 1.27 in (≈32.3 mm)
• Ring Gear Size: 8.875 in 
• Ring & Pinion Gear Ratio: 3.08 and up (numerically higher) 
• Product Weight: approx. 27.74 lb 
• Cover Bolt Count: 12 bolts

Included Components

• 1x Eaton Detroit Truetrac Differential Assembly (Part # 912A579)

Product Description

The Eaton 912A579 Detroit Truetrac is a high-performance, helical-gear style limited slip differential engineered for vehicles fitted with the AMC Model 20 rear axle. It is designed to deliver superior traction in demanding conditions - off-road driving, towing, work truck duty, or simply aggressive street use - while maintaining quiet, maintenance-free operation. With 29 splines and a 1.27-inch axle shaft diameter, it matches closely with stock components in many Jeep and Hummer AMC 20 rear ends, making it a popular upgrade or replacement when open differentials prove inadequate.

Fits numerous Jeep models from the mid-1970s through the mid-1980s and many Hummer models into the late 2000s. The differential automatically biases torque to the wheel with traction without any intervention, preserving drivability in daily use and responsiveness when conditions require. Note: this unit requires 3.08 (or numerically higher) ring & pinion ratios and compatible axle shafts. Installation may require checking carrier bearings, ensuring proper backlash, and using the correct torque on cover bolts.