FIXED: Problem with S4's Rear Diff Lock

["David Bray" <panacea@istar.ca>]

My nightmare is finally OVER!!!

Thanks to:
  Jim Dupree
  Kirby Smith
  Steve Buchholz
  Chris Miller
  Michael Williams
and all listers who expended cycles reading & thinking about my problem.

My rear diff is no longer locking on its own.  The cause ... the vacuum
check (non-return) valve as suggested by both Jim Dupree and Kirby Smith,
then supported with more analysis and information from Steve Buchholz.

I broke down and purchased the complete set of Bentley manuals (about $380
Cdn, including all taxes).  One look at the diagrams convinced me that you
guys were right on the money, even though the dealer (after umpteen hours of
diagnoses) was certain that it was a wiring issue.  In fact, the service
manager said _We haven't worked on too many of these newer quattro drives,
just the old vacuum operated ones.  We know about those._  It would seem
that they can't read their own service manuals, if they can't see that it's
still vacuum operated. It's also clear to me that they didn't _waste_ any
time troubleshooting it, just trying to get some codes, and following some
blind advice, goodness knows from where!

BTW, the dealer quoted me $57 Cdn (taxes in) for the check valve.  My
mechanic friend just happened to have a distributor retard valve (about $2)
which looked similar but was slightly smaller, and worked the same way.  We
installed it and everything works perfectly now.

Thanks guys ... I'm deeply grateful.

Many thanks also to Chris Miller and Michael Williams whose suggestions were
much appreciated (what you guys told me will be invaluable for maintenance
later).

David Bray
Ottawa, ON, CANADA
panacea@istar.ca
ICQ# 2896073

'93 S4 - modified to over 300hp
(previously, '90 90Q - amazing handling, but a little shy on power)