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re: RE: Quattro Info? (& problem with S4's Rear Diff Lock)

"David Bray" <panacea@istar.ca> wrote in panic:

Just in case anyone missed it, the problem is as follows:
Unless I accelerate EXTREMELY gently, the rear differential lock comes on
BY ITSELF!  Even though it is designed to automatically disengage at speed
(25 mph ?), it doesn't.  It's certain that the diff. IS in fact locked
because I can feel the *skipping* tires when turning.  (Of course, the ABS
also becomes disabled.)
A different guess.  If the diff lock actuates under no vacuum, then there
may be a failure in your vacuum system check valve allowing the pressure to
rise whenever you step on the gas.   The speed limit function (at least on
my 90q) is driven by a signal from the speedometer circuit and wouldn't
affect a vacuum leak.  If you can get to the vacuum lines (assuming your car
uses them) you might try a MightyVac or equivalent to keep them under vacuum
and see if it makes a difference to your symptoms.

                .... Kirby   (Kirby A. Smith)
                              2 x 1988 90q
                          New Hampshire USA