Mark Houlahan
Tech Editor, Mustang Monthly
June 14, 2013

If you daily drive your '79-'04 Mustang, chances are you've grown accustomed to the clunks and bumps coming from the rear over anything but smooth asphalt. The original design of the Fox chassis rear suspension is an engineering and financial compromise of grand proportions. You can almost imagine the Ford engineers arguing for a parallel-link four-bar rear to the bean counters, who in turn probably just kept shooting them down by spouting budget numbers and deadlines. Nevertheless, the non-parallel four-link suspension found its way under the new Fox chassis and we had to live with its short comings for 25 years—with only minor improvements/Band Aids—until the '05 Mustang debuted with its all-new parallel three-link design and fixed Panhard rod.

The design of the Fox four-link utilizes four control arms, two lower arms parallel to each other that locate the axle in the wheel housing and two upper control arms mounted at an angle to the lower arm that locate the axle laterally. These upper arms are the main issue with the Fox rear suspension, as they were designed to do two jobs: locate the axle AND prevent the axle from moving side to side. The control arms themselves are made from stamped/formed steel in a U-shaped configuration with standard rubber bushings at each end. The shape/design of the stock control arms, along with the softness of the OE rubber bushings, allows for a lot of play in the rear suspension as the bushings, as well as the control arms themselves, flex under load. Adding years of service and often well north of 100,000 miles means worn bushings and even fatigue cracking of the control arms is common.

While there are upgraded suspension offerings on the market that really improve the Mustang's four-link setup by enhancing stability, traction, and handling, many require chassis modifications, welding, and so on, not to mention their relatively steep price points.

If you're looking for a budget solution to help your Mustang's rear suspension improve on the OE design without needing anything more than basic hand tools to install, then you should consider upgrading to aftermarket tubular control arms with urethane bushings. The aftermarket arms offer increased strength and rigidity through their solid tube design that resists flexing. The urethane bushings included with these aftermarket arms also reduce flex via their higher durometer materials.

There are literally a dozen or more manufacturers of tubular control arms for the '79-'04 Mustang with as many options, including billet aluminum, powder-coated steel, fixed end bushings, adjustable spherical rod-ends, and much more. While all have their benefits and detractions, for the majority of our readers looking for a nice basic replacement set of control arms, the standard powdercoated control arm set from Mustangs Unlimited certainly fits the bill.

Our Mustang coupe has seen a lot of miles and hard driving, so it had the typical Mustang rear axle clunk over speed bumps, railroad crossings, and the like. A quick call to Mustangs Unlimited for their '79-'98 control arm kit (PN 215563R, $139.95) means that we'll have improved traction, better handling, and best of all no more clunk!

Photo Gallery

View Photo Gallery
13. To finish the installation, simply return the coil springs to their home between the chassis and lower control arms, then raise the axle housing to relocate and secure the bottom mounting points of the shock absorbers. Although not required for urethane bushings, it’s good practice to do final tightening of the suspension mounting bolts with the full weight of the vehicle on the suspension. Reinstall the antisway bar using the stock hardware. Lastly, to return the parking brake cable brackets to their rightful position, you’ll have to bend the locating tabs as shown so they’ll sit flush on the new lower control arms using the antisway bar attaching bolt. Alternatively, you can drill and tap a hole for the bracket, though many people simply leave them off.