Detroit Truetrac - GM 8-7/8 12-Bolt 30-Spline

The Detroit Truetrac - GM 8-7/8 12-Bolt 30-Spline is a no-slip limited-slip differential designed for drivers who demand controlled traction without the noise and maintenance headaches of a full locker. Built for GM's 8.7-inch 12-bolt rear axle, this unit sits between a standard open differential and an aggressive locking design, making it ideal for street-driven trucks and performance vehicles that see occasional spirited driving. Whether you're upgrading a Chevy truck, Blazer, or muscle car, the Detroit Truetrac delivers predictable handling and improved cornering grip while maintaining everyday drivability.

The 30-spline architecture uses Detroit's proven Truetrac mechanism—a helical-gear design that automatically transfers power to the wheel with more traction without requiring driver input or electronic controls. Unlike clutch-type limited-slip units that fade under heat or locker-style components that cause binding on tight turns, the helical design maintains consistent bias ratios (typically 1.5:1 to 3:1 depending on application) across acceleration, deceleration, and cornering. This mechanical approach ensures reliability in street and light off-road use; the 27.47-pound unit is engineered to OEM specifications and fits directly into the factory 8-7/8 housing, requiring only standard rear-diff service procedures during installation. No modifications to existing axle shafts or housing are needed.

This differential is best suited for daily drivers and weekend warriors who want better traction than open diffs provide but prefer silent operation over the clunking of a selectable locker. It's compatible with any GM vehicle using the 12-bolt 30-spline configuration, including Chevrolet C-10 through C-30 trucks, Blazers, and muscle cars from the 1960s through 1980s. Installation requires removal of the factory differential carrier; have a qualified shop perform the swap and refill the housing with quality synthetic gear oil to ensure long service life and optimal performance during aggressive acceleration or loose-surface driving.