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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Thursday, December 15, 2016 2:20 AM
What's the front bump-travel like on the S550? It seems like quite a few modern McPherson-strut-equipped cars suffer from inadequate bump-travel. Dive into a bumpy corner under hard braking and the lack of travel manifests as a near total loss of front-axle grip. Many modern performance cars are quite heavy, making shorter, stiffer springs a go-to solution for reducing body-roll. Unfortunately, this modification only exacerbates any issues with bump-travel.

This problem is especially pronounced on our own tuning platform, the Hyundai Genesis Coupe. It's probably the worst offender among all modern sport-coupes. With the "Track Pack" springs it only has something like 1.5 inches of compression before the front suspension hits the bump-stops. This is only made worse by popular lowering springs such as those made by Eibach.

How does the S550 compare? Have you noticed a trade-off between bump-travel and body-roll, or does the stock suspension have enough extra travel to where it isn't much of an issue?
Thursday, December 15, 2016 8:08 AM
Clicking onto this article from the homepage took me straight to page 4.
Thursday, December 15, 2016 8:30 AM
StrangeLiform, After lowering the S550, with just about any lowering spring on the market, there is almost no bump travel before the bump stops start compressing. The bump stops on these cars are longer than a normal bump stop, and they are also very progressive.
Thursday, December 15, 2016 6:01 PM
Could also be due to stiffer springs and stock dampers. You should consider upgrading the shocks if simpler modifications don't significantly improve ride quality.
Thursday, December 15, 2016 6:06 PM
You should not use the word 'dampeners' in place for a shock, or damper.
Thursday, December 15, 2016 6:18 PM
On my Mac-strut DD car, I was having a significant amount of front-end 'bounce' after installing H&R lowering springs w/ Bilstein HD dampers. I thought the front end wasn't properly damped, but then I decided to do what I could without buying new shocks.

I did everything I could to remove weight from the the front-end. That helped tremendously.

Now, the part that I didn't expect....adding stiffer engine mounts! Apparently, the engine 'bounces' around completely un-damped on the soft stock rubber, and upgrading this to new, harder durometer rubber almost completely resolved this problem

Next, I found that the radiator support bushings were crap rubber too. Well, the radiator weighs a ton, so I upgraded the radiator bushings with some custom polyurethane pieces I carved out from a PU endlink.

Wow, what a HUGE difference. The front is super tight on the freeway now. No bounce or shimmy.
Thursday, December 15, 2016 10:37 PM
Jeez talk about using parts due to sponsorship instead of buying parts that actually work.

Just say that Steeda sponsored the build.

The MGW is far far superior in everyway other than going to a push down conversion which doesn't matter to me.

The Steeda Subframe support system is junk along with the bracing.

You'd be far far better off with the BMR CB005 cradle lockout which centers the cradle, stabilizes it and adds a jacking point. Instead you need the Steeda bushing supports, braces and the delrin inserts.

I've owned all of these along with that K member. Not only did it not fit but it also hits everything because it sits so low. BMR makes a brace that ties into the Front LCA mount and its flush to the subframe so it doesn't impede ground clearance.

I have the Steeda diff inserts, Steeda trans insert and Steeda camber arms.

I'm a firm believer that no company can be a one size fits all, but half of these parts you chose are inferior.
Thursday, December 15, 2016 10:57 PM
The clutch return spring rate is a bizarre issue.... I'm curious what Ford's benchmarking data shows or their marketing data for arriving at the spring rate that they did.
Friday, December 16, 2016 9:34 AM
It's actually a clutch assist spring. This is part of the band-aid to mask the poor release load characteristics of a self-adjusting pressure plate.

Looking at graphs of the the load curves with and without the spring gives a pretty good indication of what the intentions of this device are. At first, it holds the pedal up a bit to keep it from rattling. As the pedal is pushed, it quickly goes over center and becomes an assist mechanism, inducing a milder over-center feel.

By adding it, the clutch take up is unusually vague. My guess is that this helps sell the car off the lot by avoiding embarrassing stalls during the test drive. While it is hard to feel exactly where the clutch is starting to engage, the spring makes it easy to take off without stalling.

If the OE clutch is upgraded to a performance unit (non-self adjusting), the clutch assist spring is really not in sync and is best removed. With the stock clutch, a lower spring rate would definitely be desirable to anyone who has more than a few hours of experience driving a manual trans.
Friday, December 16, 2016 12:42 PM
Am I the only one thats not a fan of a really short shifter? I prefer it close to the steering wheel, the idea of reaching inside the shifter cutout to shift doesn't appeal to me...
Saturday, December 17, 2016 3:03 PM
Ah jeez, more complaining about the shifter. I don't get it. I had an '11 S197 brembo car and yes, that shifter was not great, though I sure as hell have driven far worse in far more expensive cars. I thought most of the problems with it were actually MT82 issues, people complaining about gear grind and that's not the shifter doing that. My '16 S550 PP is a world apart from that, I have zero issues with the shifter in it. That little tiny wee short shifter just doesn't look appealing to me.

I see guys talking about installing autoblip and other such aids because they can't heel/toe/rev match downshifts. I wonder if it just isn't a little skill and driver finesse lacking? I've been heel/toe shfting for 49 years now, on the track and street, and this shifter works great for me.

I also don't get a "bounce" as described here, this car rides light years better than the S197 and handles far better to boot. I have to question adding braces and such to this car, the last thing it needs is more weight. Kripes, for a DD that sees a bit of track now and then how much stiffness do you really need?

I totally agree with the clutch spring fix, the 35 lb one makes a world of difference in clutch feel. But then I hear people bitching about the clutch pedal being heavy with it in there. Just can't win I guess!
Monday, December 19, 2016 12:10 PM
Warm, I'm with you. Not a fan of lowering the height of the shifter. It should be close to the wheel, you shouldn't have to reach down for it. Shortening the throw a bit is ok, but combining that with a lower shifter is too much and reduces feel.
No race car I've ever seen lowers the shifter. If anything they raise it to be almost level with the wheel.
Wednesday, December 21, 2016 2:36 PM
@ Hap
I had a '14 S197. completely stock the shifter is ok, but sucks if you're trying to shift fast. a fast 2-3 shift was impossible (if you say it is, you're not shifting fast enough). I got the Barton 2 post shifter bracket and it fixed all my issues. I was able to shift as fast as I want in any gear without issue. a full shifter assembly upgrade isn't needed in my book. but I'm not sure if it'd be the same deal on a S550 chassis
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