Ford Mustang Suspension Guide - Suspension Dimensions - Tech

"On the S197 Mustang, there are actually still four suspension links, but three of them (two lowers and one upper) are only responsible for locating the axle fore/aft. This means the upper arm can be designed for minimal bind, longer effective length, and the desired geometry. The fourth link is the Panhard rod, which is only responsible for locating the axle side to side. The link can also be designed for minimal bind, much longer effective length, and desired roll center.

"It's the same number of parts, just designed in a far better way. One of the reasons this design couldn't be used on the Fox and SN-95 is that the rear-mounted gas tank meant there wasn't enough room between the axle and the tank to fit the parts properly. While there are a number of aftermarket Panhards (and even Watt's links) for Foxes and SN-95s, it's a tight fit, and it's impossible to fit a design that meets Ford's requirements for clearance, crash safety, exhaust clearance, and so on."

As Feit stated, aftermarket companies have reengineered the Fox and SN-95 Mustang suspensions to incorporate Panhard bars, among other devices, to help correct some of the inherent imperfections. Be sure to consult with the manufacturers before you purchase one of these items, as there may be issues regarding tailpipe usage/clearance.

BMR's Rockey also explained that, "Factory Panhard rods, like on the S197 Mustang, are made with small-diameter tubing and rubber bushings that allow deflection under load." Like most other aftermarket suspension companies, BMR offers replacement Panhard rods made from large-diameter, heavy-wall tubing and utilize either greaseable polyurethane bushings or HD spherical bearings. The latter are usually adjust-able versions.

"By nature, a Panhard rod will alter rearend position as ride height changes," Rockey says. "This makes it necessary to use an adjustable Panhard rod when lowering your vehicle as it allows you to recenter the rearend. Adjustable Panhard rods also become a must-have part if you're trying to fit the widest tires possible in the wheelwell."

The Torque Arm
Another item that many aftermarket manufacturers offer is the torque arm. The stock Fox and SN-95 four-link design angles its two upper two control arms outward, which means the lower and upper rear control arms are not parallel, and as the suspension moves, the upper arms are twisted in their bushings. According to the folks at Griggs Racing, during performance driving, the stock rear set quickly leads to a near total binding of the rear suspension, called "roll bind." With the axle bound, it acts like a giant antisway bar, causing the rear roll stiffness to skyrocket and the overloaded rear tires to lose traction and spin. This is why the rearend snaps and fishtails when cornering, and why the rear tires break loose at the dragstrip once the body starts rising from the initial power hit.

Griggs Racing's answer is the use of its torque arm and either a Panhard bar or Watt's link to provide the necessary axle location. This is followed by the removal of the stock upper arms. Roll bind is then impossible, and the tires freely follow the pavement.

Use of two locating devices, such as a torque arm and either a Panhard bar or a Watts link, separates control of the fore-and-aft engine and braking loads from the lateral suspension loads, offering more precise suspension control. Griggs also noted that at this point, the rear roll center is now defined by the Panhard bar or Watt's link instead of the upper control-arm angle. In stock configuration, the stock Mustang's rear roll center is far too high, which overloads the outside rear tire and causes oversteer. By lowering the rear roll center with the Panhard bar or Watt's link, it's possible to get the rear tires to carry more of the load so the rearend will stick longer.