Re: rear differential not locking

[Steve Manning <stephenm@ix.netcom.com>]

At 08:45 AM 12/17/97 -0800, you wrote:
>I have searched the archives for awhile, and even posted a message a couple
>of days ago and have heard nothing.  Is the diff lock 1) so reliable that
>no one has had a problem with it, 2) so complicated that no one messes with
>it, 3) hard to trouble shoot, or 4) everyone is too busy driving in the
>snow and holiday shopping to waste time on the list?  I usually get lots of
>suggestions and helpful ideas.
>
>Quickly, my problem is that the rear diff does not engage when I press the
>button on my '89 90q.  I don't know too much about the system, but after
>looking at it, it appears to simply be a vacuum system that moves a lever
>in the diff.  Is there a good place to start looking for the problem, pump,
>hoses, fuses, (not the differential I hope)?  The system did engage on its
>own while going 65mph on the freeway a couple of weeks ago.  Does this give
>anyone any clues?
>
>If anyone has any ideas, please let me know.  Thanks.

My estimate from BTDT:  75% of the time a rear diff problem on the '88-91
90q is caused by a vacuum leak, 10% of the time it is a stuck lever on the
diff, 10% of the time it is the diff lock switch itself, and the other 5%
is up to the Audi gods.

Trace the vacuum lines from the intake manifold, back under the back seat
where it is T'eed, then back to the rear diff to see if they are actually
connected, and leak free.  If everything is OK, then disconnect the vacuum
line at the diff, apply your own vacuum (use a Mityvac or such) and see if
the lever moves.  If it does, check your diff lock switch.  Its location is
very subject to spillage, dirt, etc. and it can become flaky.  If that's
not it, e-mail me and I'll try to come up with something
else.............SLM

Steve Manning:  stephenm@ix.netcom.com
...Physical home: Metro D.C. area, USA
.....Virtual home:  http://www.stationwagon.com