Rear differential lock always on

Robert Rossato rossato.qlist at
Mon Apr 26 04:07:33 PDT 2010

Maybe it's a short wheelbase thing.  All I can say is that I've never
experienced that on any of the C4 chassis quattros I've driven.  With tires
ranging from snows to 255/40-17s.  Radek's problem could still be a locked


-----Original Message-----
From: Huw Powell [mailto:audi at] 
Sent: Monday, April 26, 2010 2:17 AM
To: Robert Rossato
Cc: 'Cody Forbes'; 'Radek'; quattro at
Subject: Re: Rear differential lock always on

ABS, haha, long dead.  Relay pulled, switch gone. The rear is not 
locked, everything is different when I do that.

Robert Rossato wrote:
> 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
> 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
> light on by chance?  That comes on when you engage the rear diff lock,
> 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
> rear diff lock is internally stuck.  Try crawling under there and see if
> can engage/disengage manually.
> Bob

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