When Ford was planning the '62 Fairlane, with 221/260ci small-block V-8 power, it found an immediate need for a light-duty, removable-carrier rear axle that could stand up to the torque. The 8-inch, removable-carrier rear axle is a scaled-down version of the 9-inch axle. Ford used the 8-inch axle across a huge variety of applications in compact and intermediate-size vehicles from '62 through the early '70s. You can expect to find the 8-inch in most small-block applications (except High-Performance) and some six-cylinder packages. For example, Mavericks and Comets equipped with the 250ci six all had 8-inch rearends with five-lug hubs. The same is true for the Granada and Monarch with 250ci sixes.
Although enthusiasts have generally viewed the 8-inch rear axle as the one to toss as horsepower has increased, there is renewed interest in this Ford axle these days. Currie Enterprises, for example, is marketing an aluminum 8-inch carrier, which is lighter and much stronger than the factory cast-iron case. You can fill it with Limited Slip, also from Currie, and have a terrific differential that will stand up to greater amounts of power.
If you're building an 8-inch differential, there are a couple of issues to be mindful of in the process. First, choose a '67 and up case, which is stronger than those we find from '62-'66. The '62-'66 8-inch case has horizontal ribs across the front of the carrier, with less iron around the pinion pilot. From 1967, the case has both vertical and horizontal ribs, plus more iron around the pinion pilot, which makes it a stronger case.
All 8-inch axle assemblies were fitted with 28-spline axleshafts. Did you know the 8- and 9-inch axles used the same axleshafts? The 31-spline axle, available in the 9-inch, will not work in the 8-inch. A large-bearing 9-inch axle will not fit the 8-inch housing either.
Small Bearing, Large Bearing
How do you identify a small-bearing 9-inch housing from a large-bearing housing? You can do this without having to pull the brake drum and axleshaft. The small-bearing 9-inch housing has 3/8-inch brake backing-plate bolts, which take a 9/16-inch socket. Large-bearing, 9-inch housings have 7/16-inch brake backing-plate bolts, which need an 11/16-inch socket. Axle bearing size was determined by gross vehicle weight. Large-bearing 9-inch housings were used in Fords with a higher gross vehicle weight.
Another quick way to identify small and large-bearing housings is brake size. Most small-bearing housings had 10-inch drum brakes. Large-bearing housings had 11-inch drum brakes.
Lightweight 8-inch Carrier
Currie Enterprises introduces the new Alumin8 differential carrier for 8-inch Ford axlehousings. The Alumin8 looks sharp, weighs less, and gives you the strength of a 9-inch axle without the weight and drag. You may polish the Alumin8 or you can install it as is. The Alumin8 is made from super-strong 206 aluminum alloy, which means great strength, without the weight. This little gem is a Currie exclusive.
 |  This is the '67-and-up 8-inch...  This is the '67-and-up 8-inch differential carrier, with a Currie Limited Slip unit in the middle. Note the abundance of support ribs from '67 and up, which gives us strength. Expect to see C7OW-A and higher on this one. |  This is the '62-'66 8-inch...  This is the '62-'66 8-inch carrier casting. Note the horizontal ribs and the absence of an oil-filler plug. Expect to see C2OW-F through C6OW on this case. |
 Whenever you're building an...  Whenever you're building an 8-inch rearend, be mindful of the oil-filler plug situation. From '62-'66, the oil-filler plug is in the axlehousing, which means there is no oil-filler plug in the carrier. Use a '62-'66 carrier in your '67-up axlehousing and there will be no way to check the axle for lube. This same rule applies to 9-inch axles as well. Make sure your carrier has an oil-filler plug if you're using a '67-up housing. |  | |