Ford Differential Builder's Guide

This is the 7-1/4-inch integral carrier differential used in light-duty applications like we find in the six-cylinder Falcon, Comet, Mustang, and Fairlane. We call this an "integral carrier" differential because the differential is an "integral" part of the axlehousing. Axle ratios are 2.83:1, 3.00:1, and 3.20:1. Most common are 2.83:1 and 3.20:1. If you want economy, use the 2.83:1 ratio. If snap is more important, opt for the 3.20:1 ratio instead. Believe it or not, Limited Slip was available, though quite rare.

The most common Ford differential/axle combo was the 8-inch removable-carrier unit. We call it a "removable carrier" because the differential bolts to the axlehousing as a separate unit. The removable carrier is nicknamed the "pumpkin," "chunk," or "third member" by enthusiasts. We call this an 8-inch differential because it has an 8-inch-diameter ring gear. Available ratios are 2.79:1, 2.80:1, 3.00:1, and 3.25:1.

The 9-inch removable-carrier rear axle is Ford tested tough. Like the 8-inch unit mentioned earlier, the 9-inch is a two-piece axle with a removable differential carrier. The 9-inch axle was produced a variety of ways for Ford's heavier-duty applications, like fullsize Galaxies, pickup trucks, and big-block V-8 automobiles. This guy is easily identified by its size. Axle ratios range from 2.55:1 to 4.30:1 from the factory. Shown here is a later-model 9-inch housing with a flange instead of a conventional yoke.

This is the 7.5-inch integral-carrier rearend used in the '74-'78 Mustang II and the '79-'84 Fox-body Mustangs. Like the 7-1/4-inch axle mentioned earlier, the 7.5 has the differential and axlehousing in one unit.

Removable-carrier Ford axlehousings play out like this. The 8-inch Ford (top) is the bread and butter housing common to nearly all small-block and large six-cylinder Ford applications. This one is common to '62-'66 Ford compacts because it has the smaller axle tubes. They are tapered toward the flanges. Midway is the 9-inch Ford axlehousing we find in the '65 Mustang fitted with the 289 High-Performance V-8. Note the tapered axle tubes for Mustang and Fairlane. Also note the rounded differential cover common before 1967. On the bottom is the '67-up 9-inch housing with the bulge. Also note the uniform tube size common from '67 and up on all removable-carrier axlehousings.

Axle tube size with 8- and 9-inch rear axles is easy to understand. Prior to 1967, you will see the tube on the right, which narrows at the leaf-spring pads. On the left is '67 and up, with a uniform tube size from the center to the flange.

From '67 and up, 9-inch axlehousings have the ring-gear clearance bulge shown here. Prior to '67, the center-section ring gear cover is uniformly rounded, like the 8-inch center section.

In 1985, Ford introduced the 8.8-inch integral-carrier rearend, which appeared first in the Fox-body Mustang GT. This is a more durable rearend that gives us the strength of a 9-inch, without the weight penalty. This is a proven differential that has performed well in nearly 20 years of use. Axle ratios range from 2.73:1 to 3.73:1 from the factory. The aftermarket offers a wide variety of ratios.