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

BY RICHARD EHRENBERG. Copyright © 2005 Richard Ehrenberg. Reprinted by permission.
First printed in Mopar Action


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.

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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 complaining
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.

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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:)

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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.)

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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.)

For more by Rick Ehrenberg, click here!

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