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Beef Up an 8.8 Rear!

From 5.0 Mustang and Super Fords
January, 2002 pgs. 48-57

Our Mark Williams Prepared 8.8 features an Eaton Posi augmented by Richmond 3.73 gears, MasterLine 31-spline axles, 9 inch bearing ends, a billet pinion yoke, and a TA performance girdle to cover up everything. Baer 12 inch brakes were shipped to Mark Williams and installed at the same time as the buildup as well.
Project Real Street gets some spunk under the trunk courtesy of Mark Williams Enterprises Our engine for Project Real Street, a Paxton Novi 2000-supercharged D.S.S. 306, will have plenty of torque and horsepower to propel us down the 1,320-or I-95 for the matter. But getting all that usable power to the ground has to be done with the right combination of parts. Since class rules dictate a manual transmission of production design-T5, T45, Tremec, and so on-we opted for the brute strength of the Tremec TKO. An aluminum drive shaft (composites aren't allowed in Real Street) will transfer power to the rear. Our last drivetrain decision became our rear-axle assembly. What should we run for best performance, strength, and ease of use?

Our main decision came down to the axlehousing. Do we keep an 8.8 under the rear of the Real Street car, or do we go with the respected but heavier 9-inch rear? Since our Real Street car didn't have a V-8 spec rear under it (heck, it didn't have any rear under it), we had to start from scratch. While a 9-inch would be great for swapping gears easily, we wouldn't be road racing or circle-track racing. Once you figure out your combination, the track's always going to be a quarter-mile in length. We also figured that most people following along will be starting with an 8.8 production housing, thus our decision was made. The 8.8 axle would be used. But where to get one? We placed a call to Mustang Parts Specialties in Winder, Georgia, for one of its used 8.8s. Since we were going to be replacing the axles and differential, gear ratio and brake type were not considerations during our purchase. We just wanted a good 8.8 housing to start with.

We had the housing truck-freighted to Mark Williams' facilities in Colorado. After discussing the project with the crew at MW, we decided to use the popular Eaton Posi unit in a 31-spline configuration along with MW MasterLine axles. To secure the axles, we had the technicians at MW convert the 8.8 with a TA Performance cover girdle and Baer 12-inch brakes. Check out Mark Williams' expert work in the photos.

Horse Sense: According to NHRA safety rules, a bolt-in device must retain all axles when running 10.99 or faster. That's fine if you're running a 9-inch, where such retention is factory. But the late-model 8.8 uses C-clips-small C-shaped retainers on the ends of the axles. If the axle breaks somehow (usually on a launch or burnout), the axle will come out of the axle tube. C-clip eliminators have been popular in the past, but we chose to go one better by using 9-inch -style axle-tube ends and their bolt-in axle hardware.

1.When the rearend housing arrived from Mustang Parts Specialties, the fluid was drained and the rearend was locked into one of Mark Williams' workstands to begin the transformation into the stout assembly proud to wear the MW logo.
2.In order to properly re-create the original track width and to machine the MasterLine axles to the proper length, several measurements are taken by the technicians at Mark Williams. The axle flange-to-pinion-center is measured for the left and right axle tubes, and the axle-flange-to housing-end (also called the brake standout) is also measured and recorded.
 3.The complete housing will be stripped and bead blasted before continuing. First, the stock C-clip axles must be removed. With the cover off and the differential cross-shaft removed, the axles can be pushed in to access the C-clips.

    4.Once the C-clip has been removed (notice the machined groove in the axle tip where the C-clip was in photo 3), the axle can be removed from the housing. This step is repeated for the other axle, and then the brakes and differential are removed from the housing.


 5.Using the measurements taken earlier, the bare housing is set up for removal of the housing ends. Knowing how long the 9-inch replacement ends are determines how much to remove to maintain the stock track width.

     6.With the measurements verified, the housing is locked down and the band saw makes quick and clean work of the cut needed. The housing is then rotated and the other housing end is measured and cut off.


 7.Before welding on the 9-inch housing end, we had Mark Williams snap this quick comparison photo of the stock 8.8 end-where the axle bearing is located-and the new 9-inch end. The 9-inch end will be able to take more load and abuse than the 8.8 end it is replacing.

     8.Next, a tool called a line-up bar is placed inside the axlehousing, running from one end to the other. This tool is secured by the differential bearing caps and extends out the end of the axle tubes. The line-up bar allows the new 9-inch axlehousing ends to be easily aligned to the existing housing tubes.


 9.The 9-inch housing end is then slid over the line-up bar and seated to the 8.8 axle tube. Once the housing end is secured and "clocked" correctly, the end can be welded to the axle tube.

     10.The 9-inch axlehousing end is 360 degree TIG-welded to the bare axle tube for strength and to prevent any leakage. These quality welds are extremely strong and will take plenty of power.


 11.To prevent axle-tube flex-which can ruin axle bearings, differentials, and wear tires-the axle tubes are also welded at the inboard ends to the cast center housing for strength. These welds are also 360-degree, which is exponentially stronger than the factory spot welds.

     12.Many rearend problems, such as excessive wear, noise, and so on, can be traced to worn or damaged bearing caps. Mark Williams has this trick billet-steel main cap for most types of rearends. The caps feature an increased cross section for more strength and holding power, and come with heat-treated hardware. The billet steel cap is shown here next to a stock Ford cap.


 13.The bearing cap must be milled to the proper installation height, which can be handled by any machine shop. Of course, if Mark Williams is building your rearend, the company can machine it in-house. Typically only the driver-side cap is replaced, as that is the main load-bearing side of the differential under acceleration.

     14.With all our machine work and welding completed, the MW in-house spray booth makes quick work of our freshened 8.8 housing. Once the housing is dry, it will be moved to the final assembly area to receive the Eaton Posi, Richmond gears, MasterLine axles, and Baer brakes.


 15.Installing the Eaton Posi and Richmond gear is straightforward and has been covered numerous times before. Once everything is assembled, the technician completes final ring-and-pinion setup and checks the backlash via gear-marking compound and a dial indicator to ensure a quiet, yet strong gear pattern.
16.Final crating is done with 1/4-inch board and a custom mini-pallet just for rearend housings after the brakes are installed. Everything is secured with shipping straps for its truck-freight ride across the country. Here our axle assembly arrived trouble-free and ready to rock. 5.0