Re: Alignment techniques

[AUDIDUDI@delphi.com]

> >Although many people don't realize it, an non-centered rack can cause all
> >sorts of weird handling problems due to bumpsteer effects and the lack of
> >symmetry between the right and left sides of the car.  It's too technical
> >to explain the reasons why here but the effects of this are very real and
> >well known to anyone who's ever spent time dialing-in a race car...
> 
> Is there any easy way to tell if the rack is centered? I've got an 87
> 5000S FWD. I've taken off the steering wheel a coupla times to wrap it
> in leather and replace broken high beam cluster. I just try to remember to
> set wheel straight before I pull it or else . . .
> 
> If there is an easy or painless way to tell if rack is centered, it might
> be good to post it to everyone so we can be sure no dealer or shop is
> taking us for the ride and screwing up our Audi steering. Having the rack
> cock-eyed and setting tie-rods to match the skew must really screw things
> up.

Sure ... count the number of turns the wheel makes from left lock to right
lock and divide by two: THAT's the point at which the steering wheel should
be pointing straight ahead. :^)

Actually, what I do is raise the front end of the car with a floor jack so
the wheels just clear the ground, turn the steering wheel all the way to the
left and use a machinist's rule to measure from the outer edge of the inner
tie-rod bolt to the inside edge of the nearest ps line fitting on the rack
... then I turn the wheel all the way to the right and measure again.  This
distance, divided by two, is the measurement you should get when the rack
is centered.

By levering against the tire with my knee while I simultaneously lean over
the fender measuring, I can nudge the rack to the correct spot without too
much difficulty.  Once I've got it where I want it, I install my home-brew
wheel plates (aka lubricated floor tiles) under each wheel and lower the car
onto them.  As the suspension compresses, the upper tile slides on the lower
tile and allows the tires to "scrub" sideways instead of binding.

[Since it's a slow afternoon and I've already gone this far, I might as well
continue and outline the basic DIY procedure for properly aligning a car at
home.  I'll try to keep it as brief as possible.]   

I then jack up the rear of the car and install a set of plates under each of
the rear wheels to keep the car at its normal ride height (did I mention I
do this on a level concrete floor?).  I then take some fishing line, loop it
around a jackstand, run it underneath the car from front-to-back and loop it
around a second jackstand.  Using a plumb-bob attached to another piece of
line, I drop a vertical reference from a small notch I made in the center of
the rear axle and move the rear jackstand around until this line touches the
front-to-back line.  I do the same at the front of the car using the notch I
made in the front subframe then double-check the line at the rear in case it
needs to be readjusted (it usually does).

>From here, I then get four more jackstands and position them alongside (but
about 2.5' apart from) the ones in front and behind the car.  Next, I loop
some more fishing line around the pair on each side of the car and, using a
36" steel rule, slide them around until there's about 2" from the string to
each wheel and the distance from the center line to the one on each side is
equal front-to-back.  From here, you then measure from the string to the rim
at front and back of each wheel to determine toe (if the distance from the
rear of the wheel to the string is LESS than the distance from the front of
the wheel to the string, you have toe-in; the opposiste is toe-out.  If you
want to convert from inches to degrees, remember that a slope of 1 inch in
57 is approx. 1 degree and scale your measurements up or down accordingly;
i.e., if your two measurement points are 15" apart and there's .5" between
them, you've got 1.9 degrees of toe.

(BTW, the same basic procedure turned sideways also works well for measuring
camber.  I have a 6' long piece of 2" square steel tube that I drape across
the engine compartment and drop a plumb-bob from to establish a vertical
reference.  If the measurment points (in this case, upper and lower instead
of front and back) are 15" apart and there's .5" between them, then you've
got 1.9 degrees of camber.)
   
The procedure described above is known as "stringing the car" and works very
well as long as you take your time getting everything set up (this includes
the time initially spent crawling around under the car determining where the
center of the front and rear suspension is located and making notches in the
appropriate spots for future use) and make sure you use some sort of slider
under each wheel to prevent the suspension from binding up as you make your
adjustments.  

Because many of these adjustments interact with each other, I always start
with camber first, caster next (when applicable), then toe; I then go back
and double-check everything to make sure nothing slipped in the process.  I
also align each wheel independently rather than settle for a "thrust-angle"
alignment where the front wheels are referenced off the back wheels instead
of the center of the car.  If you've got a FWD car and not a quattro, this
means you'll have to spend some time installing shims under the rear stub
axles (NOTE: this is NOT legal for stock-class cars per the SCCA Solo II
rule book but otherwise recommended when appropriate for those of you who
don't autocross your Audi.).

On a good day, all of the above takes me about an hour from start-to-finish
(put another way, that's about as long as it took me write this!).  I have
intentionally glossed over some of the finer details but these shouldn't be
difficult to figure out once you understand the basic process.  I will, of
course, be happy to answer any questions as time permits, but this stuff is
covered pretty thoroughly in any number of books about suspension and/or
handling... 


                /| | | |\  |   |\  | | |\  |  AudiDudi@delphi.com
               /-| | | | | | = | | | | | | |  Jeffrey Goggin
              /  | |_| |/  |   |/  |_| |/  |  Scottsdale, Arizona