Over the past several issues, we’ve taken a close look at the hardware that’s pretty much proven to make your leaf spring car hook hard and go straight. It’s all well sorted stuff, but what might not be well known is the adjustment process for a car fitted with the Cal Tracs components recommended by the folks from Classic Industries. Unlike a four-link car, which can be adjusted by way of the control arms, shock, and strut settings, a leaf spring suspension is adjusted in a different way. According to the experts, making adjustments to leaf spring cars is the same as for any other car, but the big change will be the way you deal with the back end. With Cal Tracs, changing instant center comes from the link attaching point (upper or lower hole). Pre-load settings have an effect upon the action in the back of the car and pre-load on one side of the other helps steer the car while the front wheels are in the air, much the same as an upper bar in a four-link or an anti-roll adjustment.
For the setup, try this: Starting at the front, you have to ensure that the front end is not binding. Typically, if you have “stiction” in a bushing (for example, a poly bushing), then the front end will bind. With a drag car or a street strip car, what you need is either a bearing or a rod end or a Delrin bushing in the control arm. Front springs should be “soft”. That means either a dedicated drag race spring or something like a six cylinder spring with a small block or a small block spring with a big block (engine). What you’ll need here is something in the range of 5-6-inches of travel. More is better. You’ll need a “loose” shock. With the Cal Tracs shocks recommended by Classic Industries, they’re 90-10 jobs and they’re perfect for the application. If you choose adjustable shocks, set them full loose for the baseline. You can adjust them from this point.
At the back of the car, again, check for binding. Typically, you’ll encounter suspension bind at the rear spring shackle and/or the front mount bolt (the one that passes through the spring eye). In many cases, the shackle bolts and spring eye bolts are over-tightened. Lube the bushings, too. Without the shocks and the Cal Trac bars in place, you should be able to easily push the rear of the car down several inches by hand.
Begin with the upper adjustment hole in the Cal-Trac bars. Set the preload on the Cal Trac at 1/16-inch. Some folks also do this rather than use the 1/16-inch preload: They use a dime and set up the bars so that the dime just slides out from between the spring and the load bolt. For now, set the rear shocks at full tight (extension). At this point, you’re ready to test the car. What follows are several scenarios you’ll likely encounter:
- The car works perfectly!
- The car hooks and wheelstands: If the wheel stand is huge, tighten down the front end. You can do this with the shock and/or a suspension travel limiter
- The car hooks, but starts turning the tires once it’s past the Christmas tree: Loosen the extension on the rear shock absorbers. Try loosening them by one adjustment “click” until it hooks without blowing off the tire.
- The car hooks but it pulls to the right or to the left. Add a small amount of preload to the side the car pulls toward.
- If the car hooks too hard and flattens the tires (hits the tires too hard): Move the bar into the lower front mount position and retune, using the steps above.
The most common mistake a tuner will make with a Cal Trac setup is to tune it like a big tire car. For example, if you leave off a transbrake, don’t leave with the RPM too high. That will (obviously) turn the tires. If you leave off the foot brake, use a two step. It will add consistency to the launch. With a stick shift combination, too much clutch air gap, too much clutch base pressure and too much RPM (basically a violent clutch setup) will make the car spin.
As you can see it’s entirely possible to make a little tire leaf spring care hook hard and go straight. Traction Masters? No doubt.