Project S550 Part 2: Addressing Shortcomings in the Suspension and Drivetrain

Project S550: Part 2 – Addressing Shortcomings in the Suspension and Drivetrain

by Nathan Brummer


We’ve gotten pretty familiar with Project S550 since our last update, having logged several thousand miles to date. While we’re still very much in love with the car, it has begun to reveal some of its quirks and shortfalls but, like any good relationship, we’re willing to work through these in exchange for our long-term goals. As with any good therapy session, it’s time to be completely honest and get all those ugly irritations and disappointments out in the open. We’ll start by recapping the issues we’ve encountered and then outline what we’ve done to address them.

As mentioned in the previous article, we chose the optional Performance Package at purchase. Despite all the upsides, this package has left us, and many other Mustang owners, with an annoying bounce at freeway speed, not-so- affectionately dubbed the “PP Bounce” on countless S550 forums. We haven't been able to pinpoint the exact cause, but our theory is that it has to do with a combination of the springs and dampeners in this package along with the soft rubber bushings. These three things simply don’t play well together. The bounce isn’t noticeable during normal street driving, but inevitably rears its ugly head when cruising at 65mph or above. In addition, we’re experiencing some pretty harsh wheel hop under hard accelerations. The IRS and soft bushings are undoubtedly the culprit here. While the IRS is great, we kind of expected this to be an issue going in, so we’re not really surprised. Another shortfall that we can’t say we’re shocked to see is the amount of body roll that presents itself under hard cornering. The S550 is a relatively heavy car and, despite the larger sway bars included in the PP kit, we definitely need some additional help in this department.

The opportunities outlined above are fairly serious issues, but they pale in comparison to the “elephant in the room” with Project S550 – the utterly dismal stock shifter. There are honestly no redeeming qualities to the stock shifting experience. From the squishy shifter, to the frustrating clutch assist spring, to the notchy transmission, it’s all bad and everything about shifting this car is frustrating. So, that being said, there seems like no better place to start.

Fortunately, our first upgrade is also one of cheapest and, arguably, one of the first enhancements any S197 or S550 Mustang owner should perform. Ford chose to install a super stiff clutch assist spring, which gives the clutch pedal a non-linear feel and makes it very difficult to accurately predict the moment of engagement. It’s extremely frustrating and can make even a seasoned manual transmission driver look like a first-time Driver’s Ed student. Many owners simply remove this spring immediately. However, in doing so, the resulting lack of any spring causes slop at the top of the pedal and can even cause slave cylinder damage since the force of the pedal is now constantly resting on the slave cylinder. The installation of a lighter clutch assist spring solves all these issues. The new spring is significantly softer at only 35 lb/in, which is enough to prevent pedal slop and premature slave cylinder damage, but still light enough to allow proper pedal modulation while delivering a much more consistent feel with predictable clutch engagement. Installation is straightforward – the spring is located toward the top of the clutch pedal and simply replaces the stock spring using all the factory hardware. This most basic of upgrades provides tremendous improvement, with the pedal being only slightly heavier after the install. It’s really pretty baffling why this wasn't the factory choice.

Next, we're addressing the shifter itself. S550 owners have several options here. There are a variety of different bushings and brackets to help firm up the sloppiness and, from our research, these seem to help quite at bit. Additionally, there are also numerous companies offering short-throw shifters that use the stock shifter housing. These can make for a solid solution, especially when paired with new brackets. However, when considering the install time and overall cost of the various options, we decided to go with a complete replacement shifter and came down to two finalists – the MGW Race Spec shifter and the Steeda Tri-Ax Race shifter. Both are excellent choices, with the MGW shifter being transmission-mounted while the Steeda Tri-Ax mounts to both the transmission and the body. The Tri-Ax is more similar to the stock unit but the frontmount is solid while the rear uses a firm polyurethane bushing. The other major difference is that fact that the Tri-Ax unit retains the factory-style pull-up reverse lock-out whereas the MGW unit has a push-down lock-out. With everything else being essentially equal in our minds, this small difference is what pushed us toward the Tri-Ax shifter. The Tri-Ax features a billet aluminum housing and hardened steel shift lever, which Steeda reports is 20 percent lighter than other replacement shifters and features a 30 percent throw reduction.


Here’s a comparison between the stock shifter and the Steeda Tri-Ax. The shift lever sits about an inch lower that stock and features a 30% reduction in throws. You can also see the flimsy stock bushing versus the Tri-Ax solid Polyurethane mount.
Here’s everything included in the Tri-Ax kit. Using billet aluminum reduces the weight by about 20% compared to other replacement units available.

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