Even the Chevy guys can't deny the greatness of Ford's legendary 9-inch rearend, so boldly opting to install a lesser 8.8-inch rear in a Mustang requires a compelling argument. Fear not, for such a questionable antic is more than justified. Sure, the 9-inch's virtues of strength, affordability, and ease of serviceability-thanks to its slick drop-out center section-are irrefutable. However, its 8.8-inch little brother is lighter, cheaper, takes less power to turn, and can be built just as strong. Bearing an uncanny resemblance to the GM 12-bolt, which the 9-inch is often compared, the 8.8 has proven its mettle in the world's fastest Outlaw Mustang drag cars, where countless racers have pushed them well into the 7s.
Since Fox-body Mustangs came...
Since Fox-body Mustangs came equipped with 8.8-inch rearends from the factory, we didn't have to track down a core, however, considering that the 8.8 has been Ford's bread-and-butter rearend in its performance cars, fullsize sedans, trucks, and SUVs for the past 30 years, cores are plentiful and sell for less than $100. By simply welding on some leaf-spring brackets, you've got yourself a dirt-cheap rearend for your muscle car that's just as strong as a 12-bolt. The weak link in many 8.8s are their 28-spline axles, but those found on '94-98 SN95 Mustangs boast 31-spline axles and larger axle tubes.
With such an impressive track record, a built 8.8 will laugh in the face of Project Fox's measly 775 hp. "People have run as fast as 7.50s in the quarter-mile with built 8.8 rearends, and I've had customers pull consistent 1.23-second 60-foot times with an 8.8 in nitrous cars," says Bill Buck of Bill Buck Race Cars in Austin, Texas. Bill keeps busy building race car chassis during the week, and serves as head suspension tuner on Mike Murillo's 6-second, 3,000hp, Outlaw 10.5 '93 Mustang on weekends. That said, we felt that he was the perfect candidate to not only get Project Fox caged and ready for battle, but assemble a bullet-proof 8.8 rearend for it as well.
Somewhat surprisingly, it takes very little to beef up an 8.8-inch rearend far beyond the durability requirements of even the most serious street/strip machines. For this build, Strange Engineering set us up with 33-spline axles, C-clip eliminators, 3.90:1 gears, billet bearing caps, a spool, a differential cover, a 1350 yoke, and 1/2-inch wheel studs. Such components aren't any more exotic than what's typically used in a basic rearend build, a testament to the strength of Ford's design straight from the factory. Furthermore, the only additional fortifications necessary were some custom chromoly back braces, and welding the axle tubes to the differential housing. At the end of the day, parts and labor for our super-duty 8.8 rearend rang up at just under $1,800. That's about $500 cheaper than a comparable 9-inch equipped with goodies like a nodular iron case and Daytona pinion support. Plus, building an 8.8 makes for a much more interesting story than merely ripping open a wooden crate and stabbing a turnkey rearend assembly under a car.
| WHERE THE MONEY WENT |
| Item: | Part No: | Price: |
| Strange axles, spool, studs, C-clip eliminator | P2000FM | $629 |
| Strange differential cover | R5234 | $149 |
| Strange billet aluminum main caps | H1124 | $88 |
| Strange 3.90:1 ring-and-pinion | RSF888390 | $160 |
| Strange 1350 yoke | U1630 | $89 |
| Strange installation kit | R5231 | $94 |
| custom chromoly bracing | N/A | $300 |
| axle tube welding | N/A | $100 |
| rearend assembly labor | N/A | $150 |
| Grand Total: | $1,759 |
C-clip axles are prohibited...
C-clip axles are prohibited by the NHRA in cars running 10.99 or quicker, so the rearend was prepped for a Strange C-clip eliminator kit. Installing it requires cutting off a small portion of the axle tube outboard of the backing plate flange. Bill suggests leaving 1/2 inch of tubing in front of the flange to allow enough space for the backing plate to mount and self-center upon.
After disassembly, our 8.8...
After disassembly, our 8.8 was pressure washed and degreased inside and out. Just like when cleaning an engine block, removing the grime helps reveal cracks and imperfections. Since the axle tubes were to be welded in several locations, they were stripped down to bare metal.
Simple physics dictates that...
Simple physics dictates that any bracing will be most effective when extended as far outboard as possible, which in this case is the inner portion of the control arm bracket. Custom bent from 1.25x0.95-inch chromoly tubing, the lower brace hugs the bottom of the carrier housing while the front braces attach next to the area of the housing that surrounds the pinion yoke. Note the two 7/16-inch holes that are drilled in the carrier housing in preparation for the front braces.
Under severe loads, the axle...
Under severe loads, the axle tubes in an 8.8 can sometimes rotate inside the differential housing. Welding this weak point is an obvious solution, but the procedure is tricky since the differential housing is cast iron and the axle tubes are DOM steel. Using nickel rods, Bill MIG welded the tubes to the housing by carefully controlling temperature buildup to prevent cracking the metal.
While the ends of the back...
While the ends of the back braces can easily be welded onto the steel axle tubes, Bill prefers attaching them to the carrier housing with Grade 8 bolts. After drilling a 3/8-inch hole on each side of the carrier reinforcement ribs, steel locating tabs were bolted in to help position the lower brace. Next, the lower brace was welded to both the axle tubes and locating tabs.
Although 31-spline axles may...
Although 31-spline axles may have sufficed for our application, we decided to play it safe with 33-spline units instead. These top-notch Strange Pro Race axles are made from the company's proprietary Hy-Tuf steel, which is an ultra-strong, low-carbon, high-nickel, manganese alloy. Combined with through-hardened heat treating, these axles yield superb torsional strength and ductility.