by Joe Palazzolo
(Taken from Ford Differentials: How to Rebuild the 8.8 and 9 Inch by Joe Palazzolo)
A common and effective upgrade is to replace the Ford 8.8-inch axle’s semi-float axle shaft retention with the Ford 9-inch-style wheel-end retention for superior strength in high-performance applications. This requires modifications to the axle housing and a set of unique custom axle shafts. If you are already upgrading to 3-tooth axle shafts, consider this upgrade at the same time. The axle shafts are straightforward and just a purchased item. Decide whether to use a sealed ball bearing or the tapered set 20 bearing arrangement. If you are going this far, opt for the set 20 upgrade. If you use tapered bearing set 20, it’s difficult to remove the axle shafts without damaging the seal or trapping it on the axle shaft.
The steps required for the housing modifications are covered below. Surprisingly, the cost to modify the housing is relatively inexpensive, but shipping the axle to a business, such as Currie Enterprises, can be somewhat expensive. Depending on the condition of the housing, this upgrade can cost as little as a couple hundred dollars without the price of the new axles and is far superior to the aftermarket C-clip eliminator kits.
The first step is to fixture the axle in an industrial-style cutoff saw. This saw has a very precise vise to precisely support the axle housing. It does take some time and effort to get it aligned. Once it is in the fixture and measured perfectly, the stock wheel end flange is cut off. The measurements are based on how long the wheel end flange is and referenced from the center portion of the axle housing. The team at Currie Enterprises has performed this operation so many times that they have the measurements for most common axle configurations. This saw is huge and makes quick and accurate cuts of the housing.
Once the end of the axle tube has been trimmed off, the cut is straight and true, so it looks like this. When machining any housing, a burr is left on the inside and outside of the tube wall that needs to be removed. Use a hand deburring tool for the inside of the tube while a hand file can be used for the outside of the tube.
The outside surface is carefully cleaned up and a chamfer is ground on the outside of the tube for the weld. Although hand tools can be used for this operation, an electric angle grinder was carefully used to chamfer this axle. As always, patience and care must be taken with this type of work. The inside diameter is also cleaned up just as carefully. A flapper wheel style sander disc was used on the inside of the tube and marks quick work of the task. This is the prepped end ready for placement of the alignment fixture and new wheel hub flange.
A special set of collars is inserted in the center portion of the axle that simulates differential bearings. These collars can be seen in the photo clamped in the bearing caps. Also, the tight fit bar is aligned with the collars. This bar is inserted through the entire axle tube and properly aligns the wheel hub before it’s tack welded in place. Even though these collars and shaft are only required once, they are a necessity to get this alignment correct.
A similar collar is clamped in place on the wheel end side of the axle. This collar and shaft arrangement serves to perfectly align the wheel hub flange for welding. On the top of the new flange, a half circle is machined in the flange, which provides clearance for the wheel speed sensor. This modification is performed on the latest Mustang 8.8-inch axle housing. Also, both the axle housing and the new flange have been chamfered for the weld.
A MIG welder, .030-inch wire, and the correct setting for the wall thickness of the tube is used to tack weld the new flange in place in four spots, which are equally spaced around the tube. This may take some practice based on the welder used and I recommend practicing on the old cut-off wheel hub for the correct welder settings. With the flange now aligned and secured, the entire housing assembly goes to another unique turntable style tool for final welding.
The entire axle housing is placed in a special modified lathe style tool. This custom-built tool is just for this purpose and is a must for any good custom axle shop. As you can see by the entire bench layout is just for this type of axle housing welding. The axle housing is carefully installed in this tool and a roller support rest allows the weld operator to easily spin the axle housing when welding. During the weld process, a foot pedal controls the speed of the rotation of the axle housing, and the operator must adjust rate of rotation while he is welding the housing. Skill and practice is necessary to correctly do this each and every time.
The completed weld is structurally sound and leak proof. There is the perfect heat-affected zone and weld penetration along with the perfect amount of overlap on the weld end to ensure it never leaks. All that is left now is to clean up some of the weld spatter and clean up any debris on the inside of the tube thoroughly. With just a few coats of primer and paint, this unit is ready to be assembled.