The Root of the Problem
Solid-axle-equipped Mustangs were manufactured with a four-link rear suspension design that requires the rear upper control arms to do two jobs. One job is to locate the axle laterally. Unfortunately, compromises in the design of the Mustang four-link prevent the rear axle from being precisely located. The axle will shift from side-to-side by up to 2 inches. This inconsistent movement of the rear axle causes a rear-steer effect.
Rear-steer means that the rear of the car is steering itself, without any steering input from the driver. This rear-steer behavior makes the Mustang unstable, and requires corrective action by the driver. This can make the driver feel very uncomfortable, as they do not have complete control of the rear of the car. While that four-link design might be suitable for a commuter car, it cannot provide the handling prowess expected of a high performance vehicle.
The MM Panhard Bar Solution
The MM Panhard Bar adds an aluminum rod as a lateral suspension link between the rear axle and the Mustang chassis. This simple design precisely controls the side-to-side location of the axle to eliminate rear steer. The unstable and unpredictable feeling typically associated with the Mustang four-link suspension is gone, making your car safer and easier to drive!
Why choose a MM Panhard Bar, and not a Watts Link?
There are two good methods of controlling the side-to-side location of a rear axle, a Panhard Bar or a Watts Link. MM's Engineering Team chose the Panhard Bar because it allows a much lower roll center than a typical Watts Link design. A lower roll center reduces the tendency for the inside rear tire to lift and unload during cornering. As a welcome bonus, a Panhard Bar is far less complex, less expensive, lighter, and allows for the use of tail pipes!
Upper Control Arm Bushings
Whether or not your Mustang is equipped with a MM Panhard Bar, it is very important that the rubber upper control arm bushings be retained. This is one application where the compliance of a rubber bushing is a benefit. Retaining the rubber upper control arm bushings is a necessary compromise to achieve acceptable handling. See the Rear Lower Control Arm section here for more information about control arm bushings.
How it Works: The Complex Interactions of a Four-link rear suspension plus a Panhard bar
As the suspension moves, the rigid Panhard Bar causes the Mustang's rear axle to move through a different, and better path than the stock four-link design. This requires the upper arms to physically change length as the suspension moves. Obviously, the metal control arm cannot change length. But its effective length, the distance between the control arm's two pivot points, can change because of the inherent compliance of a rubber bushing. If the ability of the upper control arms to change their effective length is hindered by a noncompliant bushing material, the suspension will bind up, and not move freely. The resulting restriction in the ability of the rear suspension to freely articulate will cause poor handling; the car will have a tendency to oversteer, and it may do so in a sudden and unpredictable manner.
Unique Features of the Maximum Motorsports Mustang Panhard Bar:
- MM's Panhard rod is the longest possible at 38" between pivot points. This minimizes the amount of the rear axle's lateral movement due to the arc of the rod's travel. The longer the rod, the larger the radius of the arc. The larger the radius, the smaller the sideways movement during bump and droop travel.
- A single slot on the MM chassis mount allows for vertical height adjustment to keep the Panhard rod level at different vehicle ride heights. A level bar minimizes lateral motion over the range of suspension travel.
- Large 3/4" rod-ends are mounted in double shear at both ends.
- The unique design and quality materials of the MM axle and chassis mounts ensure they are strong enough to not break, and stiff enough to not flex, even when cornering loads exceed well over 1 G.
- Maximum Motorsports' boxed panhard bar axle mount bracket encloses the rod-end for a rigid, non-flexing mount.
- The MM chassis bracket mounts to the rear frame rails of the car, not the flimsy trunk floor or spare tire well.
- MM's exclusive frame panhard bar frame inserts fit inside the rear frame rails. These provide a structurally sound attachment point for the MM Panhard Bar chassis mount.
- The MM Panhard Bar is designed to clear the factory tailpipe routing. Aftermarket tailpipes that follow the factory routing, such as Flowmaster and DynoMax will clear the MM Panhard Bar without modifications.
- The MM Panhard rod is mounted as low as possible to lower the Mustang rear roll center height (which is essentially at the same height as the rod). A low roll center reduces the tendency for the inside rear tire to lift and unload during cornering. The roll center height of the MM Panhard Bar is considerably lower than what can be achieved with a Watts Link.
- The Panhard rod itself is a lightweight aluminum tube. It is available in either natural finish or polished. The identical item is used on NASCAR stock cars.
- While a properly installed MM Panhard Bar is compatible with the standard T/A differential cover, we do recommend the new low-profile T/A cover to ensure there is no interference.
The next logical step after the installation of the MM Panhard Bar is the installation of a MM Torque-arm. Upon installation of the MM Torque-arm the rear upper control arms are be completely removed. This solves the bushing deflection problem, and finally removes the last source of binding in the rear suspension. Maximum Motorsports also has complete MM Torque-arm Suspension System packages.
Note: If you have a Baer brake system with PBR calipers on the rear of your 1994-04 Mustang, you will need the MM Caliper Relocation Brackets.