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Re: rear differential not locking

In a message dated 12/17/97 Jad.Duncan@GAT.COM writes:

<<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?>>

What speed were you going when you tried to engage the rear diff lock? My
recolection from when I owned a Torsen center diff q is that the rear diff
lock only works below something like 10 mph. The intent is to use it to get
unstuck and it will turn itself off above that speed in the event you forget

As far as how to troubleshoot it, you will most likely need Bentley in hand.
Are you sure the system engaged at 65? Perhaps what may have really happened
is a false indication of it locking (hello Audi electrical gremlins???). I'm
not sure what is underneath that switch as my 88 80q was new and in warranty
so I never tore into it. There must be some electronics involved that ties to
the speed sensor for the automatic deactivation to work. In turn this circuit
must control the vacuum actuater in some way. Without Bentley in hand more
thought is pure speculation but I hope this points you in some direction...

Mike Veglia
87 5kcstq