Budget 10-Bolt Upgrade

The ’67-’69 Camaros are probably the most sought-after and popular performance cars Chevy ever built. If you have one, then you know that finding a 12-bolt rearend for it is even harder than finding a president with high moral standards. The 12-bolt is coveted mainly because it’s as strong as the standard 8.2-inch ring-gear 10-bolt is weak. Abuse an 8.2 10-bolt and it’ll break. Sure, you could bolt in a 9-inch Ford, but there is a more elegant solution that’s also downright inexpensive.

GM enthusiasts assume all 10-bolts are weak. While for the most part this is true, there is one exception—the GM 8.5-inch ring-gear 10-bolt. The truth is the 8.5-inch 10-bolt is almost as strong as a 12-bolt since its ring-gear diameter is only 0.375 inch smaller than a 12-bolt (8.50 versus 8.375 inches) and the pinion gear shaft is an equal diameter. Even better, the 8.5 rear axle assembly was the universal rearend for millions of GM cars and trucks from 1971 through 1996. This means there are a bazillion to choose from.

Our pal Tim Moore, of Moore Automotive, turned us on to this low-buck rear-axle swap for the early Camaros. The corporate 8.5-inch 10-bolt was first used in ’71 Camaros (the ’70 Camaro retained the 8.2) along with several other body styles, including the second-generation Novas. While the Camaro might seem the likely swap, the ’71-’81 Camaro rear axle is 1 inch wider and employs a wider leaf-spring mount. The ’72-’75 Novas also used the 8.5-inch housing and its dimensions make it a bolt-in for first-generation Camaros. But this is just the beginning.

While ’72-’75 Novas offered gear ratios from 2.73 to 3.42 both with and without posi units, most came with open differential 2.73 or 3.08 gears. After dozens of recycling-yard jaunts, Moore has discovered that many ’71-’81 Firebirds and Trans Ams came with posi units that can be purchased relatively cheap. As for gear ratios, Moore likes to look first in ’77-’94 ½-ton Chevy trucks and vans equipped with the 8.5-inch ring gear to find the 3.42 gear sets.

Moore recommends purchasing a bare 8.5-inch housing unless it’s already equipped with a posi and the right gears. By purchasing the gears and posi separately, he can usually find all three major components for less than $200. Chevy’s famous interchangeability comes into play here as well since the stock ’67-’69 Camaro 8.2 brakes and axles will bolt right on the Nova 8.5-inch rearend. What could be easier? Before assembling the rearend, Moore recommends buying a Federal-Mogul rearend assembly kit (PAW offers a great price on these) that includes all the bearings, seals, and small parts you’ll need to assemble an 8.5-inch ring and pinion. The only other parts you’ll need are a pair of new axle bearings.

The only other major expense involved with this swap would be paying someone to set up the ring and pinion. This can cost around $200, which could drive the entire cost of this swap up to as much as $400, but this is still cheap. Even at this price, that’s a third the cost of building a similarly equipped 12-bolt or a Ford 9-inch. This is a classic example of how to use inexpensive factory parts to create a very strong drivetrain that will last for decades in even the most brutal street/strip applications.