Written by Jason Reiss
Photography courtesy of GForce Performance Engineering
Let’s face it, chassis bushings are decidedly unsexy performance parts. They aren’t shiny, billet, or covered in a high-visibility hue to catch the eye. Properly performing bushings are mostly out-of-sight, out-of-mind components that aren’t even thought about until one or more fails. But according to Jesse Powell and the fine folks at GForce Performance Engineering, they can make all the difference in your high-powered performance car that utilizes an independent rear suspension.
Traditionally, OEM bushings are made of soft rubber. While this material is excellent for compliance over bumps; reducing noise, vibration, and harshness; and delivering a quiet ride, rubber bushings are in no way designed for high-performance applications. These components can be thought of as cushions for the suspension. When an enthusiast is looking to improve performance, bushing replacement is often one of the first places to turn. Traditionally performance bushings are manufactured from polyurethane, but as Powell explains, not just any polyurethane is ideal when looking at the S550 Mustang chassis.
“The Mustangs in particular have always struggled with NVH issues. With the S550, it appears to be especially prominent. This becomes all too clear when you install a one-piece driveshaft. When you put a driveshaft in and there’s a vibration, 9 times out of 10, it’s not the driveshaft at all. The driveshaft has become a tuning fork, a speaker, an amplifier for the harmonics that are in this car,” he said. “The magic bullet is reducing motion without inducing NVH,” Powell elaborated. “When you put a driveshaft in the car, there are going to be some sacrifices. Everything is mounted to the chassis as it’s all one unit, and all of those harmonics go up through the body. When you start upgrading the suspension in the rear, a lot of guys say they can feel it in the seat of their pants, the roof of the car, and see it in the rearview mirror.”
To combat these problems that have become the bane of the S550 owner, G-Force collaborated with Australia’s SuperPro. The companies have developed bushings that offer the proper amount of compliance and performance for IRS-equipped vehicles—S550 Mustangs today, with Challengers and Chargers in the pipeline—that have a ton of power. GForce released the new ProBushing line, which combines the benefits of rubber bushings on the street to ensure a smooth, comfortable ride, and on the flip side, the performance of a solid mount at the track, which will help to prevent costly equipment failures like those seen in the IRS axles and even the differential case. Interestingly, it was a video posted on the internet that showed Powell and his team that they had to figure out a better solution.
“Based on some of our research and findings, we knew that pinion movement was an issue and was plaguing these cars. What we underestimated was the amount of cradle movement that was occurring under there,” he said. “After stumbling upon an older video posted by an engineer who mounted nothing short of seven cameras and an accelerometer under his car during a couple of passes, we realized just how much of an issue this was and that we needed to start engineering a solution immediately.”
“We have calculated as much as 7 degrees of pinion movement +/- during a single pass! That video shows us that the cradle was pulling away from the body by as much as an inch—like it was trying to spit it out the back of the car,” Powell explained. “We knew then we needed to educate people on the critical nature of bushings to help their driveline parts live under these power levels, and also the importance for us to design bushing kits that would not only hold up, but enhance the driving experience of these vehicles.”
Rather than force customers to use a system that solidly locks out the differential bushings and removes nearly all movement—but can introduce prodigious and unwanted NVH—the GForce/SuperPro design gives them another option.
An introduction for Powell from Aussie shop owner Rob Herrod of Herrod Performance to Graham Scudamore-Smith of SuperPro started the ball rolling on this project. They ultimately decided together to search for a bushing design that could provide OE-quality performance at idle, but remain firm under power to stop cradle movement on the Mustang and Mopar rear suspension designs.
Over the past year-and-a-half, they’ve tested several different bushing compounds and configurations and have finally settled on the current design as being the best of the best to achieve the goal. Testing with no less a racer than Jon Lund Sr.’s 7-second Mustang verified the performance of the design. Lund had broken several differential housings and driveshafts trying to find the right solution for his high-powered S550. Once the ProBushings were installed, he was able to go out and win TX2K without any failures. More testing with a Mopar racer proved to be just as fruitful: no failures and a happy racer.
The configuration of the bushings is twofold.
“It is truly a dual compound. The main piece is pressed into the same position as the factory that’s meant to really absorb the NVH. On load, when those things start working, the pressed-in, much-stiffer polyurethane piece is designed to lock it out to minimize the amount of movement each bolt has. This limits pinion movement and cradle movement in the car, which keeps the U-joints alive and your diff from point-loading and snapping an ear off the diff,“ Powell explained.
Applications for 2015-2020 Mustangs are available now and GForce is finalizing the design for Mopar cars currently. Meanwhile, the company began working on configurations for the Sixth-Gen Camaro platform. Although there has been a bit of a pause in that process due to the coronavirus shutdown, Powell assured us that the company is working on making these ready to go soon.
Ultimately, bushing replacement is a small thing that makes a significant difference in performance, and anyone with one of these cars looking to hit the track should invest in the upgrade. It could save a lot of money in the long run.
“The key is allowing it to move enough and using the compound that will absorb the NVH and not transfer it,” sums up Powell.
GForce Performance Engineering