Our 8.8-inch axle assembly arrived safely strapped to a shipping pallet via FedEx ground freight. The assembly, as built here, minus brakes, set us back $2,100. We had to pick up gear lube (DTS suggested 90W-140 for break-in) and a Ford replacement axle vent assembly (PN E4LY-4022-A, $13).
We're itching for the day we can bolt on the wheels and tires to our Factory Five Roadster and roll it out of the garage. It'll be the first time since early February when we placed it on four jackstands for the beginning of the project. While we're only about halfway through the project, making it a "roller" will be a big turning point for us. There's still the drivetrain installation, lots of wiring, body fitment, painting, and more before the project will near completion, and then we still have to title, register, and insure the car. With so much to do, we'll take the small victories anytime we can.
Of course, we can't bolt up our wheels without suspension and hubs/drive axles. In Part 3 in the August issue, we installed the majority of our Roadster's suspension parts. This month, we take delivery of a custom-built axlehousing and bolt the Factory Five mounting brackets to it for installation into the Roadster's frame.
Next month, we'll install the rearend and brakes. Then we'll be able to get our wheels in place. Once they're on, we can set ride height via the adjustable coilover shocks and torque all of the suspension hardware one final time.
It doesn't really matter what 8.8-inch housing DTS starts with since it cuts the axle tubes to the proper length for the application. We had the company install 9-inch Torino bearing ends to the axle tubes. This is a much safer way of securing the axleshafts to the housing than the stock C-clips the 8.8 uses. If you want the whole 9-inch package, DTS offers 9-inch housings for late-model Mustangs that will work in the Factory Five application as well, including the FR/9 housing with improved geometry for better traction.
As many of you know, the Factory Five Roadster is based around using donor or new parts designed for the hugely popular '86-'04 V-8 Mustang, including the drivetrain. For the rear-axle portion of our build, we had several options, including installing a 9-inch Ford housing designed for said Mustang model years, or a production Mustang housing, again from said model years, which is Ford's corporate 8.8-inch housing with integral carrier gear design. The 8.8-inch housing is immensely popular for its strength and light reciprocating weight, and can be found in everything from Mustangs to F-series trucks, Explorers, Crown Vics, and Lincoln Town Cars. Even classic Mustang owners are swapping to the 8.8s, but that's another tech story.
The '86-'93 Fox Mustang housing is what the original Factory Five dimensions are based upon and offers the widest rear-wheel choices because it is the narrowest Mustang rear at 5911/44 inches. The '94-and-up rearends grew wider as the body style changed and disc brakes were added. If you are on a budget, the stock 8.8-inch housing will work fine for a donor build, but with the 500 hp we'll have on tap, we decided to build something a bit stronger while still allowing bolt-in functionality of the Factory Five suspension parts.
We contacted Drivetrain Specialists (DTS) in Michigan for some ideas. We knew we wanted the narrowest rear possible for some serious rear rubber, so DTS obliged by building us a "Fox width" axle assembly and stuffing it with all sorts of goodies from Eaton, Strange, Ford Racing, and more. After discussing the details with Mike Rosales at DTS, he had his guys Adam, Patrick, and Josh break out the welder and pull the parts from stock to build us one tough rear axle. DTS not only offers parts for most any rear for repairs and upgrades (such as gears, bearings, and seals) but it can custom build just about any rearend you can think up-such as our 8.8-inch unit for our Roadster-including custom fab work, powdercoated housings, brake kits, and so on.
The factory 8.8-inch housing uses a cast centersection with steel axle tubes. The tubes are pressed into the cast center and then a weld "button" is used to secure them. To prevent axle tube distortion under power, it is common practice to weld the tube to the centersection. Here the axle tube and centersection have been ground clean in preparation for welding. | 
Pat from DTS carefully welds the joint in a 360-degree fashion, using a custom work stand that allows him to rotate the housing during the welding process. The axle tubes are checked and straightened during the process, and the billet 9-inch ends are welded after the tubes. | 
Here's the completed weld that prevents the axle tube from moving in any way. We've seen a few 8.8s leak oil from this joint, so the weld will prevent this as well. |
The 8.8-inch housing is an integral carrier design, which means the differential and gears are installed into the housing and not a removable carrier or "pumpkin" like the older 8-inch or 9-inch units. We opted for an Eaton Posi unit for this axle build. The Eaton Posi (PN ED 19588-1, $505.60) is a tough unit, with 400 pounds of preload and 31-spline side gears (more splines equal more surface area for strength). | 
As you can see by the exploded-view diagram, the Eaton Posi is a clutch-type differential. The clutches use super-tough carbon fiber for the friction plates. Forged gears add even more strength to the unit, and the whole thing is rebuildable, just like a stock Ford Traction-Lok. | 
When swapping rearend gears, it's smart to install all new bearings and seals. This was pretty much mandatory since DTS started with a bare housing from its inventory (you can send the company your own housing as well). This complete bearing, seal, and shim kit (PN IK 83-1013 $128) has Timken bearings for the differential and pinion gear, ring-gear bolts, cover gasket, pinion nut, gear-marking compound, and more. |