Bolt-in axles include (right to left) the axle, retainer plate, split washer shim, press-on bearing, and housing end. To remove the axle shafts, you need to remove the four bolts.
The rear cover’s shape and the number of bolts are identifying features for GM rear differentials. The round 10-bolt cover with a bulge for the ring gear identifies this axle assembly as an 8.5-inch 10-bolt. The two lugs on the lower case at the 5 and 7 o’clock positions are also identifying features. The 8.2-inch differential does not have these lugs.
7.5/7.625-Inch Units
To positively identify the Chevy 10-bolt in the 7.5/7.625-inch size, you need to measure it because it is very similar to the 8.5-inch housing. The case has a similar pair of lugs at the base of the center of the housing, which are located at 5 and 7 o’clock. However, the 7.5-inch lugs are smaller, with the outer side running at an angle and the inner side cut with a radius. The oval-shaped cover measures 8
A pair of long flat areas on the front side of each axle tube is a clear indicator of an 8.5-inch Chevy 10-bolt.
To help you identify the 8.2-inch housing, remember that it may have an irregular-shaped cover or a round cover, but it does not have lugs as on the 8.5-inch.
Chevy 10-Bolt Models
Although the 8.5- and 8.6-inch rear axles are more than capable of handling 400 hp (and with some setups a bit more), the 10-bolt name has a bad reputation due to the inherently weaker 7.5 and 8.2 designs. Because these two sizes are so common in pre-1971 (8.2) and 1975–2002 (7.5) vehicles, the 8.5 is lumped into the same group. This design was used in all GM rear-drive cars from 1964 through 1972. The 8.2 was phased out starting in 1971; it was replaced by the 8.5-inch “corporate” 10-bolt, and was installed in everything from Camaros and Chevelles until the mid-1980s. It remained in the 1/2-ton trucks until 1999, when the 8.6 replaced it, using the same basic design.
By far, the most common 10-bolt is the 7.5/7.6, and it has been around since 1975. It was installed on small trucks and vans up to the 2005 model year. There is very little aftermarket support for this axle assembly because it couldn’t handle high-horsepower loads and therefore its performance potential was marginal. In street applications, the 7.5 is good for 350 to 400 hp with street tires and lots of wheel spin. When sticky traction bars and/or sticky tires were installed, owners found that 400 hp can quickly turn the 7.5 into shrapnel.
In the final analysis, this axle is simply too small for high-horsepower cars, and so these axles should be avoided for most muscle cars and certainly any racing applications. Although gear sets and a locking differential are available, these are only suitable for a mild street engine or possibly a dirt track car. In the world of dirt track racing, some classes require a GM 7.5-inch 10-bolt and because there is no traction on dirt, this rear works very well.
Millions of 8.2-inch axle assemblies were built and many can be found in salvage yards. And like the 7.5 axle, it has a fair amount of aftermarket support but the ring gear is too small and therefore it cannot handle much torque. If installed on a 400-hp or stronger engine, it often fails. And unfortunately, there simply isn’t enough room to install bigger axles, so it isn’t a viable option for a high-performance car. To support high torque and horsepower loads, the axle shafts need a larger diameter and spline count. Combined with the small outer bearing races, the 8.2 is limited to 28-spline axles.
For performance vehicles, the 8.2 can typically handle up to 400 hp with street tires, but that’s the limit for this axle. If you bolt on even a set of drag radials, the axles bend or break, along with having the potential for breaking the gears and carrier themselves. You can build these for performance, but if you use sticky tires, the superior traction and consequent strain from the grip will kill it quickly on the drag strip.
There are temporary fixes for the 8.2, such as a carrier girdle, but they don’t provide a reliable and suitably strong solution. When too much torque or traction is fed through the axle, it will eventually break the axle.
The 8.5- and 8.6-inch 10-bolts have larger ring-and-pinion gears, which makes an important difference. These rear axle assemblies can handle up to 400 hp. Among the Chevy 10-bolt family of axles, these provide the best performance and durability. The car versions were in production from 1971 to 1987. General Motors has been using this axle assembly in cars for 16 years and in 1/2-ton trucks for 30 years. The 2010-up Camaro uses a similar design (8.6 10-bolt) in the center section of its independent rear suspension.
The 8.5 is limited to 30-spline axles, but can withstand 1,000 hp with slicks when properly built. The factory installed the 8.5-inch 10-bolt in the Buick Grand National, and that’s the biggest claim to fame for this OEM axle. In stock form, the 8.5 can support wheel-standing launches from the turbocharged 6-cylinder. At just 3/8-inch smaller than the 8.875-inch 12-bolt differential, the 8.5-inch ring gear is strong enough for high-performance applications.
The aftermarket fully supports the 8.5. Gears of all sizes, limited-slip or Posi-Traction, lockers, and spools are offered. Affordable performance is what the 8.5 is all about. Considering the challenges of the typical 12-bolt swap for most muscle cars, when the 10-bolt units are often a bolt-in swap, the 8.5 10-bolt starts to look really good.
10-Bolt Carriers
Several differential carriers are offered for the 10-bolt axle assemblies. However, only certain gear sets are offered for the carriers, especially if you change gear ratios. Typically, 10-bolt carriers are specific to a series of gears. A 2-Series carrier holds 2.56:1 and higher gears (numerically lower) such as 2.41. These are very high gears, good for top speed, not for off-the-line performance. The 3-Series carriers are good for 2.73 and lower gears, so 3.08 and 3.73 gears work well.
Most axle assemblies have open differentials. The open differential does not have anything in the middle of the carrier between the side gears. If this were a limited-slip or Posi-Traction differential, you would see the clutch packs in the middle of the carrier and between the side gears.
The stock axles for both Chevy 10- and 12-bolt differentials use C-clips unless you have one of the rare bolt-in axle units. A small bolt in the center of the carrier retains the crossbar.