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Re: Odometer & Fuel Gauge
Posted by David Prantl (more from David Prantl) on Wed, 15 Aug 2001 00:18:58
In Reply to: , Kok Chen, Sat, 17 Dec 1988 12:00:00 

>  It just seems a little odd to me that the speedo will  work fine but the 
>odometer/trip-meter don't - aren't
>  they interconnected somehow via some gearing???

Yes.  The Odometer is driven by a worm gear from the speedo, meshing with a 
straight gear.  This straight gear has a tendency to come out of alignment 
in it's shaft for some reason, getting out-of-mesh just enough to hang up 
occasionally.  The hanging up tends to crack the gear, which makes it lose 
grip on it's shaft, and allows it to freewheel, which makes it unable to 
drive the odometer.  The earlier Swiss-made units (which your '84 should 
have) are much less prone to this problem since the gear in question is made 
of metal (rather than plastic as in the later German-made units), but is 
apparently not immune to the problem either.

The trip-meter is driven by a straight gear on the odometer, through an 
intermediate straight gear.  So, if the odometer no longer turns, the 
trip-meter will not turn either.

I have spent one whole Saturday monkeying around with one problematic 
speedo/odo/trip meter from an '89 900 (plastic-geared German-made VDO unit), 
and have managed to fix it rather nicely.  It was very tedious and 
frustrating to disassemble and reassemble the unit, to repair the cracked 
gear, and to fix it such that it would not freewheel on it's shaft anymore.  
Then I had to break out the Dremel tool for some final tweaking of the 
gear-tooth profiles to achieve a perfectly smooth mesh, thus preventing the 
hang-up problem that caused it to break in the first place.

I haven't had to fix a tank-level sender, so I can't advise on that.

Good luck.

David Prantl
david_prantlno39sdcx6spamx782hotmail.com
'84 900S, 5M, 210kMi, RIP as of 2/98
'89 900, 3A, 116kMi, restored and SOLD on 3/24/01
'86 9000T, 5M, 188kMi
'88 9000S, 5M, 142kMi
'90 9000S, 4A, 133kMi
'93 9000CSET, 5M, 72kMi
'68 97 Sonett V4, 4M, 76kMi, #000467

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