Rear differential lock always on

[Robert Rossato]

Hmmm, I wouldn't expect it to be a Torsen thing.  My S6 is essentially the
same setup as the 90Q - Torsen center diff and lockable rear diff.  The only
time I have had shuddering from the rear wheels was when I locked the rear
diff on dry pavement on purpose - just to make sure it was engaging.
Otherwise she's quiet.  Full lock or not.  

Sounds like the rear diff is stuck in the locked position.  Is the "ABS Off"
light on by chance?  That comes on when you engage the rear diff lock, which
should disengage on its own at 15 mph.  If the light is on and it's not
disengaging at 15 mph then it sounds like there might be something foofed
with the vacuum switch.  If the light is not on, then it's possible that the
rear diff lock is internally stuck.  Try crawling under there and see if you
can engage/disengage manually.

Bob

-----Original Message-----
From: quattro-bounces at audifans.com [mailto:quattro-bounces at audifans.com] On
Behalf Of Cody Forbes
Sent: Sunday, April 25, 2010 7:57 PM
To: audi at humanspeakers.com
Cc: Radek; quattro at audifans.com
Subject: Re: Rear differential lock always on

That's a torsen thing. The torsen is locking up because of the wheel  
speed differentials caused by the sharp steering angle. People tend to  
call it "torsen shudder". My A8q does it too (as should all torsen  
equipped cars).

-Cody (mobile)

On Apr 25, 2010, at 7:27 PM, Huw Powell <audi at humanspeakers.com> wrote:

> My '89 90Q does that, with the lock not engaged.  It probably  
> shouldn't
> but it does.  Every day when I do a full lock (steering) 180 degree  
> turn
> to leave my parking lot.  I ignore it.  My Chebby truck does it  
> too.  I
> ignore that as well. I ignore a lot of things that would otherwise
> bother me.
>
> (resisted urge to sign with four tildes...)
>
> Radek wrote:
>> H'Audi;
>> Car is a 1988 90Q.  A question I couldn't find the answer to in the  
>> Bentley:  is the rear differential lock actuator on when pulled or  
>> when pushed by the vacum thingy?  The car has a shudder coming from  
>> the rear end when turning at slow speed.  At highway speeds, no  
>> issue.
>> TIA
>> Radek