We improve the handling and ride of an S197 with a Watt's Link rear suspension kit.
writer: Frank H. Cicerale
photographer: Frank H. Cicerale
It has been a long day at work, and you relish the fact that when the clock strikes 5:00 p.m., you'll be punching out and heading home. Making the drive a bit more tolerable is knowing that sitting in the parking lot is a thundering S197 Mustang. On the way home, you get a bit frisky and take an off-ramp at a higher-than-posted speed. The car settles into the corner nicely, and you're cutting it with precision. That is, until the rearend hits a slight blemish in the road and the rear skips out just a bit, forcing you to swing the wheel in the opposite direction, roll out of the throttle, and realize that when you get home, a change of underwear will be needed.
With the advent of the S197 Mustang came a 300hp Three-Valve engine, some killer good looks, and as far as the rear suspension was concerned, a three-link, live-axle setup with a Panhard bar. While this is great for a factory car, when it comes to handling and cornering, the factory setup has its limitations. To improve performance on our S197, we cruised over to JDM Engineering in Freehold, New Jersey, to modify the standard three-link rear suspension setup with a Saleen Watt's link.
As just mentioned, S197 Mustangs roll off the assembly line with a live axle in a three-link design. A three-link suspension locates the rearend on three different points: two on either side of the rear and one at the top of the housing.
Part of a three-link's advantage is that there are many different variations as to where the links are placed. With each different link placement comes a different set of handling characteristics. In addition, a three-link is more compact than a leaf-spring (or four-link) design.
The disadvantage of a three-link is that it needs something to locate the rear axle laterally. On the S197 Mustang, this piece is the Panhard rod, also known as the Panhard bar, or in NASCAR speak, the track bar.
A Panhard bar is the component of the rear suspension that provides lateral location of the rear axle. It was invented by the Panhard Automobile Company of France in the early 20th century and has been used in many different applications since its first iteration. It's a rigid bar that runs from one side of the car to the other at the rear axle. The bar is attached on either end with pivots that enable it to swivel up and down, thus allowing the axle to move in a vertical plane only. One end of the Panhard bar is connected to the axlehousing, while the other is attached to the chassis. The length and position of the Panhard bar is what determines movement, and in a sense, handling, of the rearend.
When you tune into a Sprint Cup race and hear crewchiefs comment about raising or lowering the track bar, they're discussing using the Panhard bar to make the car handle properly in the corners. By either raising or lowering the Panhard bar, they're changing the range of motion of the rear axle, thus increasing or decreasing an understeer (push) and/or oversteer (loose) condition. While these expensive cars have adjustable Panhard bars, your street Mustang does not. When compared to a Watt's link-style suspension, the Panhard bar, as well as the Watt's link, has advantages and disadvantages. Before we get to that, however, let's see exactly what is a Watt's link.
A Watt's link suspension is a complex system that utilizes a pivot and more solid attachment points on the rear axle to keep the housing from moving side to side when cornering. Carlos Duran of Saleen gave us the scoop on the Watt's link. "With this setup, the Panhard bar is removed and replaced with the Watt's link. The Watt's link bolts on the passenger side to the stock Panhard bar mounting point, and on the driver side to an added mount. In the middle, it's mounted to the differential cover."
This type of suspension is used predominately in Trans Am racing, and more recently has been installed on the Saleen/Parnelli Jones Mustangs. The Watt's link helps to give the axle a better roll center. When it comes to roll center, there are two definitions. The one commonly used is the geometric, or kinetic, roll center, while the other is a force-based definition pioneered by the Society of Automotive Engineers (SAE).