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Get A Grip—Bolstering a modern Mustang’s suspension begins with corralling bushing deflection

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Photography courtesy of Brian Sexton

While modern muscle machines have undoubtedly improved over their predecessors, they are still built to please the masses. That means they not only must perform at a high level, but they are also expected to remain quiet, smooth, and generally polite in situations when your right foot is not to the floor. That means there must be compromises.

Even for an elevated handling machine like the 2018 Mustang GT fitted with the Performance Pack Level 2 option you see here, the suspension is better suited to carve up corners in the Nitto NMCA West Auto-X series, but it’s suspension is not ready to regularly handle the shock loads that come with dumping the clutch on a prepped track with a sticky tire.

“Having a Mustang with some serious rubber on the back (Michelin Sport Cup 2s in 305/30-19), coupled with an independent rear, when launching hard the rear wheels will hop violently, potentially damaging or breaking the axles,” car owner Brian Sexton said. “BMR’s Cradle Lockout Kit, along with the Lower Control Arm Bearing Kit and Ford Performance Toe Link Bearing Kit, and replacing the factory bushings makes the rear much more stable by reducing wheel hop to little or none at all depending on the track surface.”

Seeking more traction for his 2018 Mustang GT with the Performance Pack Level 2 option, Brian Sexton ordered a choice selection of upgrades from BMR Suspension and Ford Performance. With the hardware in hand, he headed to Coastal Chassis Dyno in Tampa, Florida, to have the upgrades installed.

Of course, there are myriad options for modifying a 2015+ Mustang’s suspension for performance use, but BMR Suspension has become one of the more popular options, which led to their selection for this project.

“BMR’s reputation for building solid driveline components for the S550 Mustang made the choice easy,” Sexton explained. “They’ve been perfecting their products for many years on the independent rear Mustang platform since it was introduced and have a lot of racers, some even running in the sevens using their products at drag strips all across the country.”

To eliminate the bushing deflection in the rear lower control arms, Brian selected BMR’s bearing upgrade for the lower control arms (PN BK081), which add a much greater degree of control to the rear suspension.

To deliver on that kind of performance BMR first looks to control the movement inherent in the factory setup that is due to the noise, vibration, and harshness targets that restrain factory engineers from turning up the performance dials too high.

“The bushing deflection within the factory S550 IRS system is very extreme,” Ford specialist at BMR Suspension, Kelly Aiken, explained. Not only is it so much that causes the S550 to have much worse traction and wheel hop problems than it’s competitors, but also so much that is a major contributor to part breakage and cracking of stock factory bushings.”

To remove uncertainty in the rear suspension and quell wheel hop, the upgraded bearings in the Ford Performance toe links take the randomness of rubber out of the toe link equation.

Sexton obviously wanted better traction from his new Mustang, but he also feared snapping a halfshaft as a result of such extreme deflection.

“The BK081, CB005, and Ford Performance Toe Bearing are the very first three modifications that anyone serious about performance should perform to their S550s IRS System. These three parts address the three areas that deflect the most under loads on any performance application,” Aiken said.

One of the most effective (and popular) upgrades that BMR offers for the S550 Mustangs is this IRS cradle lockout (PN CB005), which corrals all the movement of the IRS cradle on the chassis.
One of the easiest and likely handiest parts in this grouping are BMR’s jacking rails, which makes it easier to find a spot to jack up a Mustang from all along the side.

The parts in question are the bearing kit for the lower control arms (PN BK081), the chassis jacking rails (CKR002), the cradle bushing lockout kit, and the Ford Performance knuckle to toe link bearing assembly (PN M-5A460-M). While the jacking rails mostly make it easier to service your S550, the other gear has a direct impact on its performance.

“The BK081 removes the deflection found within the rear lower control arms. This deflection causes massive wheel hop, alignment inconsistency, bushing knock/snap back, bouncy uncontrolled ride, artificial spring rate and more,” Aiken said. “This upgrade can be compared to upgrading the rear lower control arms on 1979-2014 Solid Axle Mustangs.”

The Coastal Chassis Dyno crew started by removing the stock lower control arms.

Certainly the bushings are a big improvement, but the cradle-lockout kit offers the largest leap forward in this group of parts, as it addresses the area where much of the deflection takes place.

“Our CB005 is likely the single most popular IRS modification within the S550 Suspension industry segment. This part removes almost all of the deflection that is found within the mounting of the IRS subframe to the chassis,” Aiken explained. “The deflection found here is responsible for uncontrolled oscillation while using the car for any purpose to include simply driving to get lunch. This deflection is also a major reason for the wheel hop found on the factory S550 Mustangs.”

With the arms free, they removed the flexible factory bushings, pressed in the BMR spherical bushings, and reinstalled the lower arms.

“One of the overall biggest improvements the CB005 makes is in how the rear shocks, sway bar, and coil springs react to inputs. In stock configuration, the working function of the suspension is delayed due to having to work through the ‘dead zone’ of the IRS deflecting first—before the suspension affects the chassis movement,” Aiken added. “Think of this like dropping an anchor from your boat when you are in 65mph winds, once you commit to dropping it, you have to wait until the anchor drops to the bottom for the reaction to happen. When you commit to a turn, you have a delay before the suspension can actually work the chassis — same thing.”

The final piece of this puzzle was the addition of Ford Performance’s toe-link bearings, which complement the BMR parts by stabilizing the rear suspension geometry.

With the lower arms reinstalled, the Coastal team replaced the stock toe links with the upgraded units from Ford Performance. As you can see the new billet links are far more rugged and eschew the inconsistent rubber bushings in favor of spherical units.

“There is a reason why this was one of the very first upgrades Ford Performance offered for the S550. Rubber does not belong on an alignment component/link. Alignment is one of the most important factors in improving performance,” Aiken said. “With rubber in the system, the vehicle simply cannot perform at its best. Swapping to the this bearing kit improves everything—it lessens wheel hop, improves braking, improves handling, and makes the car more predictable in any performance driving situation.

To accomplish the upgrade, Sexton headed to Coastal Chassis Dyno & Performance in Tampa, Florida, where Sam Lippencott and his crew deftly installed the upgrades and give this Mustang more traction.

In place of the factory cradle brace, Coastal installed BMR’s cradle lockouts, which vastly improve the predictability of the rear suspension.

Finally, they bolted on the BMR jacking rails which you can see offer far more real estate that you can use to jack up the car should you need to swap tires or do maintenance in the pits.

With all the new upgrades installed, this S550 was ready for launch.“At the drag strip I could launch the car as hard as I wanted with minimum wheel hop. There was still a little, but I was at Bradenton Motorsports Park where they are well known for their track prep and sticky starting line,” Sexton said. “Pair that with the 305/30-19 Michelin Sport Cup 2 tires I was running and you’re going to have some grip! Overall it was a lot better then before. I can now launch with confidence without the fear of snapping an axle and leaving the track with my car on a flatbed.”

Sexton moved on to another vehicle before putting too many laps on the car, but the initial runs showed that this foundational upgrade had the car on the right path for lower elapsed times.

“The car felt more solid and the rear was as if it was just locked into place, but not harsh. I could launch on the street with zero wheel hop,” Sexton said. “It would track better through the curves on my favorite back road and was just a joy to drive.”

Undoubtedly any S550 owner would likely move on to more modifications to put down even higher levels of performance, and Aiken is well versed in the strategy to take.

“A set of springs designed for the intended use that have a stiffer rear rate to plant the tire harder, as well as an adjustable shock with the bias of the adjustment toward the extension/rebound control,” Aiken added. “The S550 IRS squats, a lot, so controlling the rebound (opposing reaction) is the key to consistency and efficiency when launching.”

But further mods are for another story. Until then, check out the bolt-on upgrades that transformed Sexton’s new Mustang at the starting line.

Sources

BMR Suspension

813 | 986 | 9302

BMRSuspension.com

 

Coastal Chassis Dyno & Performance

813 | 849 | 2423

Facebook.com/coastalchassisdyno

 

Ford Performance

800 | 367 | 3788

PerformanceParts.Ford.com


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