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 DSS GTO 9-inch Conversion...
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.
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.”
Our 9-inch third member is...
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.
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.
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.
We cleaned the inside of the...
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.
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.
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.
Greg then went around and...
Greg then went around and began tightening the nuts until the third member was flush with the housing surface.
We took off the top five nuts...
We took off the top five nuts to install the intermediate bracket. Greg ground off some material that protruded and prevented the bracket from mounting. While this may seem a bit scary to do, the modification is minimal and will not affect the case’s strength.
Once completed, the bracket...
Once completed, the bracket installed easily and Greg torqued the locking nuts.
To mount the pinion bracket,...
To mount the pinion bracket, we removed the three upper bolts that secure the pinion snout on the third member. DSS provides five bolts to replace all of these if you desire, but the bolts included from Strange were strong and long enough.
Next, Greg installed the axle...
Next, Greg installed the axle stubs onto the housing. He lubricated the perimeter of the stubs with gear oil to help them on but it’s a tight fit since there can’t be any leaks from the housing. As you can see in the photo, there is a notch cut out of the stubs to give access to one bolt at a time. Greg tightened the 10mm bolts in equal steps by turning the pinion to get them to mount flush. In other words, don’t try and tighten them down one by one—gradually use the bolts to press the stubs in place to 57 ft-lb once flush.
Here Greg test fits the rear...
Here Greg test fits the rear bracket. The top should be angled away from the housing (toward the back of the car when mounted). It’s installed loosely first and Greg will tighten it once he raises the 9-inch into place. (If done incorrectly, the bracket will touch the housing and the housing will hit the car. It will also throw off the pinion angle.)