The Eaton Detroit Truetrac Differential (Part #912A556) is a proven, helical-gear limited-slip differential designed for GM 8.5-inch (10-bolt) axles with 28-spline shafts and 2.73 & up gear ratios. Built for balanced performance and reliability, the Truetrac automatically distributes torque to the wheel with the most traction—improving control, handling, and stability in both on-road and off-road conditions.

With its all-gear design, the Truetrac operates quietly and requires no maintenance or special additives. It’s a durable and efficient upgrade for muscle cars, classic restorations, and light trucks looking for enhanced traction without compromising street manners.

Note: All Eaton differentials for GM 8.5"/8.6" axles require special bearings.

• Pre-1999 (Small bearing bore 2.89"): Use bearing LM102949 and race LM102911.

• 1999–2013 (Large bearing bore 3.06"): Use bearing LM603049 and race LM603012.
  Manual locking hubs are recommended for front axle installations.

Features:

• Helical-gear, torque-biasing design for automatic traction transfer

• Maintenance-free—no clutch packs, friction plates, or additives required

• All-gear construction for superior strength and long-term durability

• Quiet and smooth operation for both street and performance driving

• Designed for GM 8.5" 10-bolt axles with 28-spline shafts and 2.73 & up gear ratios

• Ideal for restoration, towing, and high-performance applications

Specifications:

Fitment:
Compatible with GM 8.5-inch 10-bolt rear axles, commonly used in classic GM cars and light-duty trucks.

• 1971–1989: GM, Chevrolet, Pontiac, Buick, Oldsmobile Passenger Cars – Rear 10-Bolt C-Clip (2.73 & Up)

• 1972–1989: GM Half-Ton Trucks – Rear 10-Bolt C-Clip (2.73 & Up)

• 1978–1989: GM ¾-Ton Trucks and Vans – Rear 10-Bolt C-Clip (2.73 & Up)

Ideal Usage:

• On Road: Street & Muscle, Restoration, Drag Racing, Circle Track, Work Truck / Towing

• Off-Road: Light Trail, Sand Sports, Work Truck / Towing

This Part Fits: