RatchMatic™ GM 8.5 10-Bolt Automatic Ratcheting Lunchbox Lockers

• Drop-in traction device provides spool-like equal traction to both rear tires
• Cornering forces allow the locker to unlock for wheel speed variances
• Available for both 28- and 30-spline axle GM 8.5-inch 10-bolt rears
• Works with your existing open differential carrier housing
• No ring and pinion or differential carrier housing removal required to install
• Replaces open differential carrier internals (spider gears, side gears, and pinion shaft)
• Maximum traction for off-roading or street/strip use

Update Your GM 8.5-inch 10-Bolt’s Traction Ability with This Easy to Install Locker

The GM 10-bolt rear axle, specifically the 8.5-inch variety, found a home under many a ’70s muscle car, including the 2nd gen F-body. However, it saw an extended life cycle under tens of thousands of GM 1/2-ton trucks and SUVs from 1979-2008 as well. So, whether you are looking to upgrade the traction ability of your GM muscle car or off-road capability of your GM pickup (or simply looking to beef up that 10-bolt you’re swapping into your hot rod), adding a GM 8.5 posi unit of some sort is often on the upgrade list. The main issue with most posi units is that they require extensive knowledge of ring and pinion gear setup patterns, special tools, and additional parts like bearings, shims, and more to install. An option to consider if your 10-bolt is in sound shape with a gear ratio you’re happy with is the “lunchbox locker” conversion.

Installing a lunchbox locker is straightforward and requires no special tools or gear setup like when installing a traditional locker for GM 10-bolt rear ends. With a GM 10-bolt locker kit you simply remove the spider gears, side gears, and pinion shaft from your open differential carrier and install the lunchbox locker parts in place of the bits you just removed. In a matter of an hour or so you’ll have maximum traction to both rear tires, like the function of a spool, but with the ability to have the rear tires still differentiate in wheel speed for cornering/turns on the street (not recommended for autocross/road race applications). This is thanks to the GM 10-bolt locker’s ability to decouple the outer wheel from the locking mechanism, allowing the outside wheel to spin faster than the inside wheel, maintaining the two different turning radii, and immediately reengaging the locking mechanism’s teeth in the Chevy 10-bolt locker once the wheel speed is equal again.

Built For Strength on or Off Road to Provide Maximum Traction

Available for both 28- and 30-spline axle configurations, our GM 10-bolt locker for the 8.5-inch is machined from high-strength steel and uses a strong steel pinion shaft for durability, providing maximum strength for use with sticky tires or large off-road tires. Everything in our GM 10-bolt locker kit is included for your installation, including precisely machined toothed drivers and saddles, saddle springs, shear pins, C-clip spacers, pinion shaft, and a new pinion shaft retaining bolt. All you’ll need to supply is the labor, a new differential cover gasket and your favorite gear oil to successfully install this locker for GM 10-bolt rear ends with 8.5-inch ring gears.

Best of all, no special friction modifiers or additives are required as there are no friction plates/clutches used in this style of locker. It is purely a mechanical lock up between the drivers and saddles. Note that some clicking noise or ratcheting noise during engagement or disengagement while cornering is normal with mechanical lockers. If you require something that produces low, to no noise and is more predictable in an autocross or road race environment, we suggest a traditional limited slip-style posi unit for your 8.5-inch 10-bolt. We offer both clutch style and gear style units in 28-spline and 30-spline models.