Dale Amy
March 25, 2011

We’re lucky. For years, the factory has equipped the V-8 Mustang with an 8.8-inch rear axle assembly. It has earned a reputation for hardiness at power levels well beyond stockat least, in street applications, where traction usually breaks before the rearend housing.

Even so, back when the 8.8 was engineered, it’s safe to assume that nobody on the project foresaw the day of 600, 700, or 800hp street Mustangs. Nor was the housing or its internal components designed with the high-traction torture of a dragstrip or the high-heat environment of a road-course in mind. Its integrated-carrier design also complicates gear ratio swaps. All of which is to say that like every stock component, the 8.8 axle simply has its limitations.

But, as Blue Oval fans, we’ve always had an ace up our sleeve, in the form of Ford’s venerable 9-incharguably one of the sturdiest axle assemblies ever engineered. And strength isn’t the only advantage of the 9-inch design; there’s also that removable gear case, or third member, which permits relatively quick ratio or differential swaps for swift adjustment. Of course, the 9-inch axle housing itself is a rather generic beast, seeing use in everything from muscle cars to stock cars. Luckily, the aftermarket embraces the basic design, with companies like Currie Enterprises manufacturing application-specific versions.

One of Currie’s latest variants is a 9-inch upgrade kit specific to the S197 chassis, meaning it is correctly sized and configured to bolt right in place of a factory 8.8-inch assembly, while allowing retention of the factory rear brakes and even ABS function. More than just a housing, Currie’s unit is an overall upgrade kit complete with 31-spline axles, a one-piece aluminum driveshaft, Currectrac lower control arms, and an adjustable third link.

That kit was just the ticket for a car like Classic Design Concepts’ Weekend Warrior projecta ’10 GT conceived for the 2009 SEMA show. Once its show duties are wrapped up, the Weekend Warrior will see street driving and open-track use at road courses around the country. Such an application will benefit greatly from both the greater strength and easier gear swaps of Currie’s 9-inch upgrade kit, which installs as a straight bolt-in replacement, as evidenced by our photos.

Horse Sense: You’ll sometimes hear of designs like the Mustang’s venerable factory 8.8-inch rear, with its integral gear carrier, referred to as a Salisbury-type axle (the name of an early manufacturer). Removable-carrier axles like the 9-inch are also often called banjo-style because, in someone’s mind, that’s what their empty housings resemble.

Photo Gallery

View Photo Gallery