1967 AMC Rambler - Get Your Leaf-Spring Car To Launch

Some Solutions
The oldest and likely cheapest solution is to heat metal strips and bend them around the front leaves to keep them from separating and distorting. The front half of the spring from the axlehousing forward is used like a control arm to locate the housing in the car. If you can prevent the front of the spring from distorting under acceleration, that energy will be transferred to the axle centerline, forcing it and the tire down onto the track surface.

Before we added the Competition Engineering traction bars, the Rambler would squat and unload the passenger-side tire, causing wheelspin.

The second solution is the traction bar (or slapper bar) trick that we used on the Rambler. A set costs about $160 from companies like Competition Engineering. As the pinion rotates toward the body and the axle begins to wrap, the snubber on the end of the traction bar contacts the spring eye and transfers the energy directly to the centerline of the axle, driving the tires down like a big lever. At the same time, the spring is forced down, lifting the body into the air. The distance between the snubber and the leaf eye at rest determines how hard the system strikes the tires. It's about as simple as a sledgehammer and works about the same.

The third solution is the adjustable traction bar. There is a point on your car, the center of gravity (CG), where the vehicle weight is equal front to rear. If you put a jackstand under that point, the car would be balanced in the air. Now imagine that you walk to the front of the car and lift up on the bumper. The car will rise in the front and dive in the rear. The same is true for lifting the rear bumper as the car rotates or pitches around the CG. CalTracs or Slide-A-Links have the ability to move the point of lift, or instant center (I/C), if needed closer to the center of gravity. This is helpful as you make more power and try to go faster. As the I/C is moved forward, the load on the tire is greater and less violent. As the I/C is moved rearward, there is less load delivered to the tire with more violence. The benefit of an adjustable instant center is increasing or decreasing the speed of load transfer as you begin to build more torque, or to compensate for track conditions. Since we are making only about 400 lb-ft of engine torque, the current rearward I/C doesn't produce a hit on the tire so violent that it smashes the tire down causing it to later unload and spin. As we build more power using a larger engine or nitrous oxide, we are going to play with the CalTracs bars.