The Ford 8 inch axle is a smaller version of the popular Ford 9 inch axle, just with an 8 in ring gear diameter, removable pinion support, and typically 28 spline axle shafts. Original gear ratios range between 2.79:1 and 5.43:1, and aftermarket replacement gears are available for many ratios as well.

Visual Differential Identification Without an ID tag, differentials are identified by the number of cover bolts, the distinctive shape of the cover, the number of ring gear bolts, and ring gear diameter. They can also be identified by whether the center section is an integral or dropout design.

There’s an easy way to tell an 8-inch apart from a 9-inch. All of the 8-inch case nuts can be accessed with a socket. In contrast, on the 9-inch, two nuts on the bottom at about the 6 and 7 o’clock positions cannot be accessed with a socket and require a wrench.

An 8 inch Ford rear axle was designed for use behind 6 cylinder and low power 8 cylinder engines. 175 hp to 275 hp max, with tor questions to match. The 409 engine your friend is installing will probably make 350 to 400 hp, and a lot of torque.

8.8 is fine up to 1,200hp or so. just weld the tubes, build a brace off the center section to the tubes, and weld 9in ends on it for the desired width.

There should be a tag on the diff. On bottom it will read 4 L 10. That is 4.10 limited slip.

How to Identify Ford Rear Ends

1. Locate the axle ID tag on the rear-end housing—usually a sheet-metal tag bolted to the housing, although some vehicles had a paper tag, which may be missing.
2. Decode the service number by matching it to an axle service code chart, similar to those found on WoodyG.com and Drivetrain.

The Ford 8 inch differential was supplied with Ford Falcon, Mustang, Comet, Cougar and some Ford Fairlane’s. You can purchase high quality ring and pinion sets in various ratios, high quality bearing rear end bearing overhaul kits including pinion bearings, pinion seal, crush sleeve, pinion nut, shims, ring gear bolts, marking compound and gasket.

A Ford 8-inch rearend can be a lower cost alternative to the popular 9-inch third member-type carrier, for enthusiasts with straight-six, V-6 or small-block V-8 engines. In its stock configuration, you should easily be able to transplant an 8-inch into any mid-size muscle car that has an engine rated at 300hp or below.

Both the large axle bearing, and the extra large axle bearing (some F150 trucks) had 31 spline factory applications. From about 1970 on, the big Fords, Mercury’s, and Lincoln’s has axles big enough to respline with 31 splines if they are shortened about 4″ per side.

58-59 – two dimples on back of housing, flat center band, some had drain holes. 60-67 – two dimples, flat center band, oil level hole in back cover.