Re: Flaky speedometer revisited

[steveb@newkla.kla.com (Steven Buchholz)]

> 
> A while back I asked about my flaky speedometer in my '89 200TQ. 

TEXT DELETED

> 
> Problems internal to the instrument cluster have been
> essentially ruled out.  I removed the cluster and checked all
> solder joints, traces, etc., and all is OK.  It appears that
> there is a problem with the speed sensor in the transmission. 
> My Audi dealer mechanic tells me that to fix the problem he
> needs to drop the transmission ($460 labor) and install a new
> sensor (+ $$ parts).  
> 
> My questions:  Does this sound reasonable?  Is there anything
> else I should try first?  Like, for instance, where do I find
> the ground connection for this circuit?  What specific part(s)
> will be needed?  (I think I need to buy a set of Bentley's for
> my car.)
> 
> TIA
> 
> 
> Bob  __________________________________________________      ^_____^
>     | Robert L. (Bob) Myers  <RMyers@WVNVMS.WVNET.EDU> |    /       \
>     |__________________________________________________|   (  O _ O  )
>             Love M'Audi - Love M'Bimmer.                    \  (_)  /
>        Siberian Huskies are better than either!              |  U  |
> 

Looked it up in Bentley this morning ... They don't mention anything about 
dropping the transmission to access the sending unit.  I couldn't tell much 
context from the picture, but it is probably located near the drive shaft 
flange on the drivers side of the transaxle.  The troubleshooting sequence 
was:

Remove connector from S.U.  Turn on ignition.  You should measure 12 volts 
  between the outer 2 contacts.  If this is found to be true ...

Remove the SU from the transaxle and connect it to the electrical connector.  
  Slide the rubber boot back to expose the back of the electrical contacts. 
  If viewed from the back end of the connector with the release bail on top, 
  you should be able to measure a signal that switches between 0 and 8 volts 
  on the left and center contact.

If all of this stuff works properly I'd recommend running a couple of wires 
from the terminals noted above to allow the tach/dwell/duty cycle meter to be 
connected as I mentioned in the previous post.

All that now said ... the dealer service guys do have more experience than I 
do.  It may be true that in their experience it is common for the drive gear 
to fail (I've never seen or heard of this).  It seems to me that you should 
be able to access this simply by removing the half-shaft and drive flange 
though.  

HTH!
Steve Buchholz
s_buchho@kla.com