How Do Traction Bars Work?by Pauline Gill
Leaf springs are flexible spring steel bars about five feet long with loops on front and rear ends that are fastened to the vehicle frame on both sides of the rear of the car. The one-piece differential drive axle is fastened to the middle of both springs. When accelerating normally, the springs provides a small amount of rotational give as the axle tries to twist backward and turn the drive wheels forward. When accelerating forcefully, the axle tries to lift the fronts of the springs, and drop the rear length of the springs more noticeably. When trying to accelerate violently, as with drag racing, the axle twists the normally straight springs into an S-shape, and the traction wheels start to hop up and down. This diminishes their traction and causes them to bounce and chatter violently. Additionally, the normally straight drive shaft from the front is forced to spin at an angle, which can cause vibration and potentially U-joint failure over the long term.
Traction bars are hefty rigid bars or tubes of tempered steel with pivoted brackets on both ends. The front ends of the bars connect to the front spring mounts on the vehicle frame. The rear brackets bolt to the bottom of the drive axle. Traction bars keep the axle from twisting backwards while it forces the drive wheels to turn forwards, completely eliminating leaf spring windup, and keeping the rear drive wheels forced down to the pavement for superior traction.
Traction bars are relatively easy for the hot-rod enthusiast to install themselves on street rods. Usually, serious racers have them installed by professionals so they can be tested and adjusted for peak performance.
Sometimes serious users of traction bars like to actually adjust in a slight amount of forward twist so that the axle assumes an exact zero twist under full power starts. Some racers still add traction bars to non-leaf spring rear suspensions such as trailing link with coil springs to provide more stability to softy sprung passenger vehicles.
The Only Downside:
Traction bars add rigidity to the rear suspension, so the cushy ride may be compromised.