1989 Mustang LX Rear Suspension Upgrade - Bringing Back The Bite

Drag racing differs from other forms of motorsports in that it is a sprint to the finish line, unlike other segments where the cars drive around endlessly looking for the finish line. The short sprint down the track leaves little, if any, room for a mistake, and there are countless variables that have to be just right for your Mustang to perform its best.

It all starts with a hard-launch that requires your tires to grip the track surface. Thankfully, '79-'04 Mustangs feature a four-link-style stock suspension, which is quite effective when modified for drag-racing applications. The rear control arms aren't parallel like a racing four-link, but the factory suspension carries similar principles.

This month, we upgrade a '89 Mustang LX with UPR Products' Pro-Series rear suspension and adjustable rear-spring kit, adjustable Strange shocks, and some new guts inside the 8.8 rearend housing. Each modification was selected to provide grip at the track without sacrificing street performance.

DMC Racing of Halifax, Massachusetts, handled the work, which included more than just bolt-in parts. The hardest segment of the installment was the adjustable spring mounts. It was easy for the DMC crew, but it might present some challenges for someone installing the parts in their driveway due to the welding aspect.

"The stock suspensions in Mustangs are great. With a few modifications you can make adjustments to help plant the rear tires and get the nose in the air. Just look at Outlaw Drag Radial cars. The only two 6-second cars on drag-radial tires are Mustangs, and both run on stock-style suspension. Most of the low 7-second stock-suspension-type cars are Mustangs," commented Dennis MacPherson of DMC Racing. "Sure, the components are different in those cars than the setup we installed in this '89 coupe, but the same basic design is shared by both."

Running fast on stock suspension goes back to the early '90s when going mid-9s was a huge accomplishment. Most racers utilized nothing more than a set of Southside bars, non-adjustable square upper control arms, and a pair of 50/50 shocks. It made for some wild rides, as the power under the hood wasn't effectively channeled to the rear tires. Fast Mustangs across the country would leave the line in a corkscrew fashion as the body rolled excessively. The Southside bars would lift the body and plant the tires rather violently due to the lowered attaching point at the rear housing--and without any adjustable components, there was little the racers could do except try to limit the front-end travel and move weight around. Some of the early heroes of stock-suspension madness include Jimmy LaRocca, Ronnie Crawford, and Tim Lynch. All three, along with many other notable racers, seemed to hit a wall (no pun intended) in the mid-to-low 9s. That is, until the aftermarket responded with adjustable components and a better understanding of how things work under the unibody.

The reason the cars acted violently was because of the dynamics of a rear suspension setup. The rear suspension's action during a drag launch is simply described as controlling the rear axle's rotation due to the driveshaft turning. The control arms limit the rear end's ability to rotate (opposite of the direction of the tires), and it transfers that energy into leverage to lift the front end and plant the rear tires. In addition to the control arms controlling the axle rotation, the rear shocks control the rate at which the rear separates from the body. The UPR Pro-Series control arms and Strange shocks will allow us to control the action of the rear and help our car plant the tires more effectively. UPR also provided us with a drag-race-style antiroll bar that will help keep the body level as it leaves the starting line.