Turn of the screw: front end alignment for performance on classic Mopars

BY RICHARD EHRENBERG. Copyright © 2005 Richard Ehrenberg. Reprinted by permission.
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After doing a quick, rough front end alignment, we needed to get the alignment angles professionally set. For years, we’ve set camber and toe adjustments on the garage floor. Frankly, setting caster that way is a royal pain. So, we simply took the car to our local know-what-they-are-doing alignment guys, Derham Frame and Axle in beautiful downtown Newburgh, NY.

Alignment is different things to different people. To the average chain-store point-the-wheels guy, it means getting the toe somewhere near zero, so you don’t hear the tires squeal while you’re driving straight ahead, and getting the camber and caster approximately equal on both sides, so you’re not back in ten minutes bitching about a pull. To the factory (back in the 1960s and ’70s), it wasn’t much better, although they cared a little about handling and steering feel/response.

While we’re working with suspension geometry that was designed 45 years ago, it was also way ahead of its time, with features that many modern cars would love to have (such as indirect, rear-anchored torsion bars with zero unsprung weight). Obviously, the Chrysler engineers knew what they wanted, and they delivered, from maximum anti-dive to near-perfect bump steer. And the published (FSM) alignment specs were, generally, very good. However, in one area, they succumbed to the desires of the marketing guys: caster.

The spec was generally barely adequate, and, in the case of manual steering cars, wholly inadequate. This was done to reduce steering effort. If you look at the big picture—the state of performance, the quality of roads, the typical driver, etc., back in, say, 1962, you probably would have done the same. But now it’s 2007. And we don’t drive like granny. And we have modern low-profile steel-belted radials, a tire design that was unheard of in the USA when the B and E-body suspensions and steering were penned in 1959-60.

There’s no doubt that we want more caster—we drive faster and we want the stability it provides. The old service manuals typically recommended no more than 1.25 degrees of positive caster, and even that number was typically not easy to achieve. They also recommended as much as one full degree negative for manual-steering cars, a number guaranteed to induce road wander and instability. We, however, are now equipped with Firm Feel’s tubular upper control arms, which allow caster (and camber) settings consistent with performance driving without having to resort to crutches such as offset bushings.

Camber’s a whole different ball game. The factory never recommended negative camber at all. (It’s negative when the top of the wheel tilts in.) They had a good reason for this: they were trying to minimize tire wear. With bias ply tires, camber is critical. Tilt the top in a bit, and the inner edge of the skin will wear out—fast. With steel belted radials, this is much less of a factor. Of course, there’s lots of other factors at work here: how stiff are the sidewalls? How much air pressure do you run? How low is the aspect ratio (profile)? All of these factors can affect the “best” (if there is such a thing) camber number for you. If you have superlow- profile tires (like 40 series), you might want a tad less camber. Ditto for high air pressures and/or stiff sidewalls. You always (always) want at least a some negative camber. Even with granny driving, there will be that emergency, kid chasing a ball, etc., requiring an evasive maneuver. Having more cornering G force at your disposal—via the more complete tread/pavement contact afforded by the “preload” that negative camber generates— is always a good thing.

Toe’s pretty simple: You need a skosh of toe-in on our RWD cars to assure that, with linkage deflection, there will never be toe out. We’ve created a neat matrix on page 97: pick your driving style, read your numbers. If you wind up with that chain-store alignment jockey we mentioned, who’s probably equipped with the latest laser, computer, semi-automated alignment equipment, and, hopefully, at least 4 or 5 live brain cells, you’ll need to stand there and be sure he doesn’t simply punch in your Mope’s Y/M/M and set it to “factory specs.” A “pre-tip” of a folded Jackson pressed into his sweaty, greasy palm usually does the trick. If you do the majority of your driving on two-lane blacktop, you might want to go a quarter-degree more negative on the right side to compensate for road crown. (What’s a skosh? Here’s a chart:)

If you read some of the older Mopar service and training publications, you may have heard of a fourth angle: SAI, or Steering Axis Inclination. This is the angle between true vertical and a line drawn through the center of the ball joints. Wait? Isn’t that caster? Yes, it is. This confuses everybody, so we’ll clear it up right now. It’s the same “line” but it’s viewed in a different plane! Caster is viewed from the side of the car, SAI from the front. SAI isn’t adjustable independently anyway, it’s designed-in. The main reason it’s helpful is in being sure that a smacked-’n’-pulled car is really straight again. It’s just that simple. And odds are your alignment guy has no idea. (Ours does.)

We used the “Max. perf. street” setting. (On our Green Brick road racer, we were pretty close to the “track” settings, although we couldn’t get that much caster, and that much isn’t desirable for street use, anyway.)

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