[s-cars] fact or fiction - diff lock relay...

Varon H. Fugman vfugman at globaldialog.com
Fri Oct 17 21:04:20 EDT 2003

Ken & all,

First just to clarify for new folks, only 92-95 cars have the push button
lockable rear diff.  The 95.5-97 cars have EDL (electronic differential
lock) which simulates a limited slip diff by applying the brakes to the
spinning wheel.

Normal behavior is for the diff to automatically unlock at around 15mph
(which is more like 24km/h).  Perfect for launching in snow and ice and
leaving all those "4x4" SUV's behind!

I too have been looking into disabling the 15mph disconnect for running ice
trials.  Of course, I'm not sure if this will be a good idea or not...
keeping the diff locked could cause some serious understeer (or other
handling anomalies) in turns... and the quattro is hard enough to drive on
ice as is.*

There is a wire feeding the diff lock controller under the back seat that
tells it when the "drop-out" speed has been reached.  IIRC it is white with
a blue stripe.  If you cut this wire (or put in a switch) I believe the diff
lock becomes full manual... and I would expect that it won't cut out by
itself at any speed until you hit the button again.

I'm hoping to try this first-hand this coming winter.  I might just splice
switch into the wire so I can try it both ways.  If I like having manual
mode available I might add a relay controlled by a button in the dash (along
with my ABS switch that I haven't finished installing yet!)

Why not just cut the wire and be done with it?  Because the only place I can
see wanting to keep the diff locked over 15mph (24km/h) would be for a
winter track or lake event.  For on-road use I want to keep the automatic
drop-out.  I think very bad things would happen keeping the diff locked on
dry or even partially dry pavement (tire wear, handling problems, possible
drive-train damage).

'95 urS6 waiting for ABS switch and diff lock manual mode

*The quattro system is fantastic for on-road winter driving... a regular
snowmobile.  Whatever traction is available it will find it and use it.  But
get out on a frozen lake where there is almost zero traction and the torsen
center diff seems to "hunt" making for unpredictable handling... applying
throttle in a turn seems to produce understeer 2/3 the time and oversteer
1/3 the time.  Almost makes me want my old predictable FWD ice trials car

-----Original Message-----
From: s-car-list-admin at audifans.com
[mailto:s-car-list-admin at audifans.com]On Behalf Of Ken Ng
Sent: Friday, October 17, 2003 3:57 PM
To: s-car-list at audifans.com
Subject: [s-cars] fact or fiction - diff lock relay...

I understand that the 92-95.5 UrS cars have a push
button lockable rear diff. and that the locking
feature is electronically 'unlocked' at ~40km/h - i
spoke to a fellow 95.5 UrS6 owner and he indicated
that there is a relay that can be removed to
deactivate the auto 'unlock' at ~40km/h... and that
somehow this permits full lock up to 100km/h...

query: 1. is this fact or fiction, 2. what happens at
100km/h that causes it to 'unlock' when the relay (if
such a thing exists) is removed and 3. what are the
adv. and disadv. of removing the relay ...


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