Steve Baur
Former Editor, Modified Mustangs & Fords
September 12, 2006

While the drag-racing crowd cringed at the sight of the independent rear suspension in the then-new '99 SVT Mustang Cobra, the road-race crowd was eager to see what it could do. Axle windup (felt through the seat of the pants, many called it wheelhop) was a prevalent problem, though, and in 2001, stiffer bushings were installed to quell the axle-snapping antics.

In 2003, the factory stepped up again with stiffer bushings and thicker axle shafts, leading to the best IRS unit yet. But the crazy corner carvers at Maximum Motorsports saw an opportunity to upgrade the IRS for serious street and track duty.

Ford was still using rubber bushings to keep noise, vibration, and harshness levels to a minimum, but most serious enthusiasts had been using stiffer materials such as urethane, aluminum, and Delrin-a durable and stiff type of plastic-for some time in the solid-axle Mustangs, with great results.

Maximum Motorsports' IRS kit (PN MMRG-22), which retails for $974.48, replaces all four subframe bushings, upper and lower control arm bushings, and the differential's bushings to solidify the IRS and make it more effective at what it was designed to do.

Usually, stiffer bushings come at a cost of ride quality and noise, but we noticed no issues of any sort with the new bushings installed. Proper installation and greasing of the bushings is essential to prevent squeaking, and makes installing them a bit easier as well.

Maximum Motorsports offers several upgrades for '99-'04 Mustang Cobra IRS units. We wanted to achieve the maximum and left no bushing untouched, by switching out all of the rubber with the urethane, Delrin, and aluminum bushings that come in the MMRG-22 IRS kit.

Removing the IRS from your Cobra is not an easy task, and one that should probably be left to the more advanced garage jockeys. We spent a couple of days learning our way around the IRS and visiting local friends' houses for various tools. Figure on 6-8 hours for an experienced shop to perform the install.

If you're going to tackle the job yourself, you'll need a drill, a complete 11/42-inch-drive ratchet and socket set, a torque wrench, and if you're going to install MM's low-profile rear subframe bolts, an 8mm Allen socket. A drill-mounted wire wheel (or something else you can use to clean out the excess rubber from the subframe bushings) is extremely helpful, as are an air compressor and a cut-off wheel.

We also employed some of the specialized tools that Maximum Motorsports has designed to make installation a bit easier, though removal of the rear subframe bushings really took its toll on the tool's threaded rod and supplied hex nuts.

After performing the installation, you'll need to set the pinion angle of the differential if you've installed the rear differential aluminum bushing kit. Follow this with an alignment by a qualified technician to ensure all of the specifications are correct. The last thing you want to do is mess up your car's handling when you've been trying to improve it with your latest round of mods.

The stiffer bushings were readily apparent on our first ride and drive, but we noticed no increase in noise or vibration. Some gratuitous smoke-shows let us know that axle windup/wheelhop was a thing of the past. Whether you want better handling or need to replace your worn IRS components, the Maximum Motorsports IRS packages have everything you need to make it work like it should.