Believe it when the manual says.....

[Andy Tiura <ATiura@engpo.msmailgw.intermec.com>]

.... make sure all of your tires are the same size, type, and equally worn.

My recently purchased '90 V8Q was sporting brand new front tires as it 
waited on the used car lot.  After putting a couple hundred miles on the 
car, I was convinced that it was intermittently fighting me for control (and 
occasionally growling and rumbling most eerily, varying with speed, load, 
phase of the moon, etc.).

Two trips to a "real" Audi dealer in search of a cause almost gave me a 
heart attack.

The first visit resulted in a $170 charge and a 'no trouble found, but we 
tightened up the steering rack anyway' report.  The second visit was a $131 
charge and a 'no trouble found, but we bent some chassis cross member that 
was rattling on the exhaust anyway' report.

I said:  "No, there's something scary going on.  Take the car home with you 
this evening and maybe you'll feel it too."  The next day the technician 
called to say that yes, he'd felt it, and his new diagnosis was the 
transmission.  (Factory rebuilt only, $6200 plus extras.)  He thought that 
it was trying to engage two gears simultaneously, hence the noise, etc. 
 Yecch!

I let them keep the car for the weekend.  (I didn't want to even see it.  I 
was almost sick at the prospect.  Jeez,  I can't afford a transmission.) 
 Besides, by then I had made e-mail contact with the esteemed "Eliot" who 
was giving sage advice about other possible causes.

Monday brought no activity.  Other customers had higher standing than the 
car that had already been there four days.

Tuesday, after further diagnostic test drives and head-scratching all 
'round.  The Technician, the shop Foreman, and myself were left debating the 
merits of Audi's "replace the whole thing" transmission service (non-)policy 
while standing in their parking lot leaning on my car.

Suddenly, the foreman dropped to his knees and exclaimed:  "There are 
different tire sizes on this car !".  Sure enough, the rears were 215/60s 
and the new fronts were 205/65s.

Actual circumferences were measured, with the "too-small" new tires turning 
out marginally LARGER than the half-worn "right sized" tires.  The wheels 
were re-arranged to place one big and one small on each end of the car..... 
and VOILA!

No longer did the center differential attempt to pit the ends of the car 
against each other.  The less-than-one-inch circumference difference of the 
front vs. rear tires was persuading the car to lock up that diff!   Would 
have been nice if Audi had snuck a little green indicator light onto the 
panel to indicate diff lock.... this saga would have been much shorter an 
much easier on my blood pressure.

A new set of "right-sized" tires all around was installed and the story ends 
happily.


Whew!


 -Andy Tiura
(still) '90 V8Q

Senior Design Engineer,
Intermec Corp.