Like the Fourth-Gen Firebird, the GTO is hindered by a sub-par rearend once engine output is increased. Unlike the Bird, however, the GTO uses an independent rear suspension and inadequate tire size to handle the 350hp LS1 and 400hp LS2. The result is drivetrain-murdering wheelhop.
To make matters even worse, this isn’t your run-of-the-mill rearend like the Firebird had. No, it was only used in the Australian-sourced GTO and that means parts cost an arm and a leg. To rebuild your factory rear, you’re looking at about $500 to $1,300 just for the few differential options. Gears? Those are going to cost you upwards of $500. Then a set of axles range from $800 to $1,300. In a nutshell, it’s not cheap—a downside to owning a rare car produced in Australia.
There is, however, another option. Since there has been a strong aftermarket following for the GTO since day one and they are admired with deity-like status in Oz, drivetrain companies went about solving the strength issue head-on.
The Driveshaft Shop (DSS), a major manufacturer of high-end drivetrain components, developed a complete rear swap that converted the car to an IRS 8.8 rearend from a Ford. Immediately, GTOs began to shatter records and not rearends. According to Frank Rehak at The Driveshaft Shop, the 8.8 did present some problems unrelated to holding capacity. “An issue we have with our 8.8 kit is that it requires the car owner to locate an IRS 8.8 rear out of a Thunderbird or a ’03/’04 Cobra,” he explains. While they can be hard to come by, they also might require a rebuild to the specs the car owner is looking for, and depending on where you look, it can cost some coin.”
The DSS GTO 9-inch Conversion Kit (PN GM9R-4; $4,400) contains two axles with a set of long and short bolts, a driveshaft, a 9-inch housing with locking nuts, stubs with four bolts per side, three brackets with required bolts, and two spacers for above the pinion with four additional bolts.
A New Hope
With the release of the ’10 Camaro came a whole new wave of parts development. Frank aligned himself with Scott Bagshaw of Bagshaw Fabrication in Mooresville, North Carolina, as he developed an IRS 9-inch conversion for the new Camaro. Since DSS prides itself on having its roots in the GM market, it was decided a conversion would be created for the GTO. Frank selected Jeremy (LS2-Goat) on LS1gto.com because he had one of the best known cars and it was the fastest six-speed GTO around. Jeremy’s Goat was put on the lift at Scott’s shop; shortly after, the drivetrain masterpiece was complete.
Our 9-inch third member is the popular S-series from Strange (PN PRF130; $1,190 plus $171 for the Trutrac upgrade). This nodular-iron center section features radial ribs for increased strength, a Daytona iron pinion support, a Detroit Trutrac limited-slip unit, 3.89 gears, and an S-series 1350 steel yoke, and it comes fully set up. The conversion kit was designed around it so we were pleased when we didn’t encounter any surprises installing it.
The Ford 9-inch features many benefits over the 8.8, not limited to its superior strength. Unlike the 8.8, to find a 9-inch all you have to do is open a catalog, select your gear ratio and differential type, and it’s shipped to you fully assembled and ready to install. No more hunting through eBay auctions or salvage yards.
The new 9-inch kit was designed around the Strange Engineering S-Series third members, so that is what we went with. Being a daily driven street car that will see road course duty, we chose a slightly more aggressive 3.89 gear (which offers some mechanical advantage over our factory 3.42) and a Detroit TruTrac limited-slip unit.
What’s In the Kit
The DSS GTO 9-inch Conversion kit comes with a 9-inch housing (not the center section/third member) and all the hardware and brackets you’ll need to install it. Also included is either a 4-inch aluminum driveshaft that has been balanced to 9,500 rpm, or for a nominal fee, it may be upgraded to carbon fiber. It features a Strange billet transmission yoke and your choice of solid 1350-series U-joints.
We cleaned the inside of the housing and installed the gasket. Letting gravity assist us, Greg carefully lowers the third member into the housing, which is resting on a padded surface.
Another highlight is the set of signature 1,400hp Pro-Level axles with rolled, 30-spline center bars. According to DSS, these axles are the strongest on the market and feature 300M races and full billet 4340 CV cages—an impressive step-up from the factory pencils. Finally, there are super-strong 31-spline axle stubs to fit most popular center sections should you choose something other than Strange. The kit also retains full ABS functionality.
We’ve heard the install is straight-forward, so we enlisted Greg Lovell from AntiVenom to assist us since he has assembled plenty of 9-inch rearends in the past. (This is not a single person job, so if you plan to install this by yourself, call a mechanically savvy friend—you’ll thank us later.) We soon realized there is a method to the madness and everything needs to be installed in a particular sequence to fit correctly. Otherwise, you’ll be left scratching your head as to why things don’t line up. Read on for the details.
Special thanks to Marc Christ (shown in lead photo) of Muscle Mustangs & Fast Fords for lending a hand.
