I was commissioned to build a custom Ford 8.8″ as a direct replacement for the original axle under a 1957 Bentley. Performance upgrades on the Bentley axle were not possible, and with the vehicle getting a modern engine/transmission combo it required an axle that could handle increased horsepower with the ability to lower the gear ratio and add a limited slip. The 8.8″ needed to be built to the same width, pinion offset, pinion angle, and wheel lug pattern as the original. The customer was turned away by every local differential shop before finding me, and I was happy to accept the challenge.
After making the appropriate measurements and calculations the old c-clip style bearing ends were cut off to narrow the 8.8″ and convert it to bolt-in style axles using Big Bearing Ford “Torino” style ends. These are the later model Ford 9″ ends with 3/8″ bolt holes that accept the tapered Set20 axle bearing. This revealed the junkyard 8.8″ led a hard life under the ’95 F-150 it came from and that the left tube was severely bent. Some persuasion on the straightening jig using chains, binders, and localized heat brought the tube within acceptable alignment to allow installation of the new housing end. Once the housing was complete the diff was set up with a modern 2-cut OEM Ford 3.73 ring & pinion, Eaton TrueTrac posi, 1350 u-bolt style yoke, and finished off with a US made TA Performance Girdle cover. A set of custom 31 spline performance axle shafts were sourced from Dutchman Axles. Due to the diameter and offset of the OEM Bentley wheels and the way in which the centers were welded it was questionable if clearance was sufficient for a disc brake upgrade, so the customer opted to use the OEM Ford 11″ drums from the donor axle.
The Ford 8.8″ as it started life in stock form. The Bentley axle sits on the floor below. The object was to build a performance axle that matched the dimensions of the original axle and for it to be installed in its place.
Cutting off the old bearing ends. Careful measuring and calculations are done before this step to ensure the width and pinion offset are correct when the new housing ends are welded on. Look closely at the tube nearest the photo and you can actually see the bend.
With the alignment bar installed holding the new bearing end in place it reveals how straight the tubes are. This side will take some work before the new end can be welded on.
The housing is set up in the straightening jig. Chains, binders, and localized heat are used to bring the tube back into alignment.
The tube is now straight enough for the bearing end to be welded on. The tube does not have to be perfectly straight, and they rarely are.
After beveling the ends of the tubes, new bearing ends are welded to the housing at the correct pinion angle. Housing width and pinion offset were determined before the original ends were cut off. Even though the tubes are not perfectly straight, the new bearing ends are in perfect alignment with the carrier bearing bores.
After completing the housing it’s time to move on to the differential set up. A modern face-hobbed 2-cut process OEM Ford 3.73 gear set is installed with an Eaton TrueTrac limited slip. The TrueTrac is a helical gear driven unit which operates seamlessly with no clutches or cones to wear out. It also boasts a hardened steel case and bearing journals making it an ideal choice for applications where spun bearing journals are an issue.
Once the differential setup is complete it’s time to install the brakes and custom axle shafts. The axle lengths were calculated early in the project after the housing width and pinion offset were determined. Finally, it’s time to install the differential girdle cover. The girdle cover has studs going through the cover with pads that rest against the bearing caps. The purpose is to stiffen the cast housing and to minimize deflection of the bearing caps under heavy load. A coat of paint is applied and the finished housing is now ready for pick up. The customer will need to determine placement of the spring, shock, and sway bar mounts once the housing is mocked up under the vehicle.
Bull Built Differentials 