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Got My Nine

Building a bulletproof Ford 9-inch with Auto Weld and Mark Williams components.
By Evan J. Smith
Muscle Mustangs & Fast Fords, September 2000
Nothing came easy in the early years of the 5.0 Mustang racing. Go-fast parts were limited to small blowers, nitrous, gears and not much else. Still, the EFI Mustang pioneers got by using age-old tricks to improve performance. As slicks went on and horsepower increased, elapsed times dropped into the 12s and then 11s, but all was not good in Mustang land. Mustangs were getting quicker, but driveline parts dropped out quicker than Mike Tyson's opponents.
At the time, a solid 5.0 driveline consisted of nothing more than a modified T-5 with a factory 8.8 rear; if you were smart you dropped in a set of 31-spline axles from a Ford truck, but that was it. Shortly there after, racers figured out how to hook better. The inception of the 90/10 struts and Southside bars hit the market and elapsed times dropped even more, and Stangs in the 10s broke parts with regularity. Axles snapped like toothpicks and Traction-Loks gave way equally as quick. (Remember, this was long before 33-spline axles, spools and T/A covers were available for the 8.8.)
To combat this breakage, many racers turned to the Ford 9-inch rear. In racing circles the 9-inch is known as a brute--infact, you can find one in everything from Stockers and Pro Stockers to Winston Cup cars.
Back then, a 9-inch swap involved making your own brackets and having custom axles cut to the correct width. Today, switching to a 9-inch is much more easily accomplished. Auto Weld of Danville, Pa., is one company that sells a killer 9-inch conversion. But there's more to it than that. Auto Weld's 9-inch also includes a nifty set of adjustable four link control arms which feature Heim joints and mount in the factory location. The bars can be tuned in length and in mounting position making the four-link system infinitely adjustable. The mounting brackets are heavily reinforced and the lower brackets also include a perch (one per side) for the rear coil springs to ride on. By placing the springs (and the sprung vehicle weight) on the rear housing instead of on the lower control arm, like in a stock Mustang configuration, the bars move more freely. This helps the system to work more like a conventional racing four link.
By design, the 9-inch is stronger than the 8.8 and there are more heavy duty or race components available for it. Ask anyone who runs a 9-inch and they'll brag about the ease of maintenance and quicker gear swaps, too. Speaking of gears, you'll find the ratio selection is broad. Virtually any ratio is available.
Realizing the benefits of the Auto Weld Ford 9-inch, we figured we couldn't go wrong selecting one for our '96 Mustang project car. Our plan is to run in Hot Street, Street Bandit and occasionally in NHRA Super Stock Modified. To do so we'll need about 700 horsepower and lots or traction. With any luck we'll be packing some heat in the form of a Kuntz & Co.-Prepared small-block Ford, which will be backed by a G-Force 5-speed. And with a race weight over 3000lbs., we'd need a serious rear.
We contacted Auto Weld for the housing and suspension links and Mark Williams for the rear end internals. Both were helpful with preparing the 9-inch for our combination. As I mentioned above, the car will be run in three classes. While ladder bars are legal in all three classes, we decided to run the stock style adjustable set-up from Auto Weld. One reason for not running ladder bar is because we wanted to keep the stock mounting location for the housing and the unibody stock in case we ever wanted to run the car in a class requiring stock chassis and suspension. Besides, we've seen Sam LaManna's car run with the Auto Weld rear and we like his results.
Using MW-supplied housing ends, Ron Showers of Auto Weld fabricated our 9-inch housing. He also installed his own brackets for the control arms and coil springs and added reinforcing material on the back of the housing and at the lower control arm brackets. Before assembly, the housing was powder-coated bright yellow (Auto Weld also offers the coating in gray) to add looks and exterior protection.
When it came to internal rear parts, we looked no further than Mark Williams Engineering. Mark Williams is known as an industry leader and Mark Williams himself was available to recommend the proper components for our combination. Since we're building a car for heads-up competition, Williams wanted us to go with top-of-the-line high-performance parts. This included an aluminum center section with lightweight axles and lightweight brakes.
In the world of 9-inch rears, there are some terms you may or may not be familiar with. In case you're not up on the lingo, let's get in touch. Naturally, the housing is the component that houses the rest of the parts. Housings can be based on a stock original unit, or fabricated from exotic materials. Housings can also be altered in width, hence the term "narrowed rear." In addition to the housing, the 9-inch has a differential. The differential is the unit that takes the rotation of the driveshaft and transfers it 90° to the axles. Differential types include a Posi or limited-slip, open, Auburn, locker, spool and a few others. Unlike an 8.8, the differential in a 9-inch does not go in through the back of the housing when it is installed. In a 9-inch there is no rear cover, either; instead, you'll find what is termed the third member.
The third member is an assembly of parts including a case, ring and pinion, pinion support, spool (or other differential), and the pinion bearings. Prior to installation in the housing, the ring and pinion are setup in the third member case. This makes installation of new gears easy, because the third member is simply bolted to the housing. There are generally four types of third member case material: cast iron (found in OE application), nodular iron, aluminum and magnesium. Mark William's lineup includes Nodular Iron, Aluminum Thru-bolt, Light-weight Aluminum and Magnesium.
For a third member, we went with MW's Pro Stock Assembly (part No. 57019). This unit has an aluminum case with a bolt-through design, meaning the carrier bolts run through the case and are secured with bolts behind the caps. The case also has Grade 9 hardware and widened caps made from 7075 T651 material. Our third member was prepared with an aluminum 40 spline spool, a MW 28-spline 1350 series pinion yolk with ball bearing support and Richmond gears.
In addition to this top-of-the-line setup, Mark Williams also offers a complete selection of thirdmember units for the wide range of performance applications and race classes. "Most customers select the aluminum because of the significant weight savings," stated Brian Balsley of Mark Williams. "But our nodular case is very strong, and can handle some serious power," he added. According to Balsley, the nodular case weights 27-28 lbs., whereas the aluminum units come in at 16 lbs. That's a big difference when weight matters.
In light racing vehicles (1800 lbs or lighter), when only moderate strength is needed, one may opt for the magnesium case, which is about another 30 percent lighter than the aluminum, but not as strong.
To match the 40-spline spool, we installed 40-spline axles (part No. 50500). These are MW's Super Light Hi-torque axles designed for race vehicles over 1800 lbs. The axles are gun-drilled to reduce reciprocating weight. And in addition, the axle are machined behind the MW name plate to make them as light as possible without sacrificing any strength. MW axles are forged from a special nickel-chromium-molybdenum alloy to provide strength and ductility. Each axle is also computer machined, heat treated in house, and Magnafluxed to insure dependability.
To stop our Mustang, we chose Mark Williams Symmetrical Brake Kit (part No. 71225). This kit is designed for heavy race vehicles, but with performance in mind. "The calipers are exceptionally compact," says Balsley, "and engineered to provide optimum clearance. The most important characteristic for a caliper's stopping ability is the bridge strength. The limiting strength factor for calipers of this type is fastener strength. All the attention over material types(forged or billet) has little effect of bridge strength. MW calipers use four 7/16-inch diameter fasteners plus a center support bushing. And all fluid passages are internal eliminating external lines that are prone to damage," he added.
In a few months we'll have some horsepower and we'll be able to put these parts to the test. We look forward to completing the buildup and getting to the track. The action in Hot Street and Street Bandit is heating up and we want to be a part of it. However, we're remaining patient because we want to put the puzzle together correctly. And when it's complete we hope to be competitively in the 9's and running against the likes of Bob Hanlon and LaManna. So stay tuned and look for our hot '96.