CalTracs
Performance Traction Bar System

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By Jim Bigley

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Big power can stress unmodified chassis and suspension components in ways that limit overall truck performance. Pushing ¼-mile times into the 13's is relatively easy. Going faster requires more power, more effort and more attention to chassis setup. The recent installation of Kennedy Diesel's CalTracs traction bar system in our Duramax Diesel hot-rod is a step toward the 11's.

With models to fit current GM trucks, the CalTracs traction bar system is a pure bolt-on upgrade to the rear suspension, that is designed to eliminate spring-wrap, wheel-hop, and maintain the differential pinion angle during full-on launches in the ¼-mile. Operating similar to a four-link suspension, the force-transfer link bar transmits forward thrust from the rear axle to a point more toward the center of vehicle mass. This translates to a weight shift during launch towards the rear for increased traction and acceleration, and with a lot less potential for driveline and rear axle damage.

Installing the CalTracs is pretty straightforward, except for replacing the rubber/steel front spring-eye bushing with the aluminum version supplied in the kit.

CalTracs recommends removing the leaf springs from the vehicle, then let a shop R&R the bushings using a hydraulic press. I'll admit that that approach would be easier in some respects, but I replaced the bushings on the vehicle. Here's how...

The first step is to pull the hardened steel sleeve out of the rubber bushing using a length of 7/16" all-thread, a large axle nut socket and an air wrench. The center steel sleeve comes out somewhat easily.

Getting the rubber bushing and its steel shell out of the spring-eye is more of a challenge. I cut through the outer steel shell with a saws-all, then used an air chisel to deform the steel shell enough to allow it to be pushed out.

Clean up the interior of the spring-eye using a small wire wheel or drum sander, then press the new aluminum bushing into the spring-eye using your length of all-thread and large washers. It goes in pretty snugly.

Once the new aluminum bushing has been pressed in, and is centered in the spring-eye, slide the greased steel center bushing through the two end-plates and aluminum bushing. Then push the spring up, and slide the bolt through the frame support and new leaf spring bushing. Tighten the spring-eye nut/bolt to 70 ft/lbs.

As the axle attempts to rotate under power, it pushes forward on the link bar. The top bolt through the CalTracs end plates then pushes down on the top of the leaf spring, preventing any further axle rotation. The amount of pre-load can be adjusted to suit track conditions or ride quality when on the street.

CalTracs includes new lower axle/spring mounts that include the brackets for the link bar. All of the steel components included in the kit are powder-coated for a durable and chip resistant finish.

Since this truck had been on the road for a number of years, I installed new U-bolts along with the new CalTracs link bar mounts. Tighten all of the U-bolt nuts equally, in a cross pattern, winding up with equal length threads showing. Again, working in a cross pattern, tighten the U-bolt nuts to a final torque of 101 ft/lbs while making sure the link bar mounts are firmly seated against the axle tubing.

For every action, there is an equal and opposite reaction. As the rear tire and wheel is driven forward (clockwise in this photo), it produces a corresponding reverse rotation torque in the axle (as indicated by the arced arrow). Without the CalTracs, this would result in deforming the leaf springs into a "S" shape. Spring wrap can result in sudden loading and unloading of the tires as they alternately slip and then bite into the track, producing what is otherwise known as wheel hop. These sudden torque load and pinion angle variations can break U-joints, damage axles and differentials, and can limit vehicle performance.

With the CalTracs, the axle rotation is restricted, thus smoothly transmitting the axle thrust forward and into the vehicle's frame.

All of the components used in the CalTracs kit are of a high quality, and the powder coating should maintain their appearance for many years to come. Best of all, wheel-hop and spring-wrap are now under control.  TDP

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