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GM 8.5-Inch Rear-ends—Worthy of Your Chevy
Back in the ’80s, it was fairly easy to find a 12-bolt rear end for under your muscle car. The strength and presence can’t be denied, but finding one today is so much more difficult and expensive that most people don’t even bother looking anymore.
This is part of the reason why so many 9-inch Ford rear ends have been put under so many input torque increases. The balanced design ensures that the bias torque of the differential is proportional to the input torque for smoother engagement. The Eaton diff also features precision-forged gears for improved strength and durability. The patented, high-temperature, carbon fiber clutches feature carbon anti-wear coating, are virtually indestructible and will maintain smooth, quiet operation over the life of a vehicle. Eaton also chose to upgrade the side bearing journals by making them larger, thicker and stronger. The aftermarket Eaton diff is a very desirable unit.
J&S Gear in Huntington Beach, California, jumped on the 8.5-inch bandwagon early on and has had tremendous success installing them in a variety of customers’ cars. One J&S Gear customer drag races an early Nova that consistently runs in the mid-10s using an 8.5-inch GM corporate rear, and he has had no problems with this setup to date. J&S Gear builds its 8.5-inch GM corporate rear ends to Buick Grand National specifications, and orders parts accordingly.
Several brake options are available for these GM rear ends, from drum brakes to iron-caliper disc brakes to aluminum-caliper disc brakes. Whichever brakes you decide upon, all parts are available through your GM dealer or local parts house. With the ease of obtaining housings, limited-slip differentials, gears, brakes and parts, the 8.5-inch GM corporate rear end should be high on your list of replacements for your high-performance Chevrolet. Leave the Ford parts to the other guys.
