All vintage Mustangs have a leaf-spring rear suspension, and while they're durable and easy to maintain, a major disadvantage is that the spring has a tendency to twist under hard acceleration. This type of load usually happens when accelerating hard on the street and more dramatically on the starting line of a dragstrip. The end result is often wheelhop, which can be violent if left unchecked. In a bad situation, wheelhop can break axles, snap springs, and possibly cause damage to the car's wheelhouse. Recall that only the leaf springs connect and locate the rear axle to the car.
For cars with high-horsepower engines, traction bars can be a good solution. Traction Master's underride traction bars-the same design used on '66 Shelby GT350s-are the perfect setup for the rear suspension on any vintage Mustang.
The bars are obviously a top-quality component, and the heavy construction of the bars themselves mean there's almost no way they'll bend. Furthermore, once in place, the bars also serve as trailing arms, solidly locating the axle in relation to the car. While some designs fasten at the forward end of the spring, the front mounting bracket of the Traction Master bars weld to the framerails under the car, providing new attachment points for the rear axle. So, the axle is no longer held in place solely by the leaf springs.
Finally, installation is easy, as the bars essentially bolt in place, save for a few minutes of welding that's required to attach the front mounting bracket. A good automotive welding/suspension shop near you (such as Marlo's Frame and Alignment, a local shop we use quite often) is the ideal place to help with such an installation.