My 560SL's speedometer was working fine at purchase, but the odometer had been out of commission for several years. I didn't give it much thought at the time, but when I got home and looked into the situation, I couldn't find much on the internet or forums, here included, on repairing the newer electronic speedometer/odometers. Lots of info. on the old ones with the simpler worm gear driven odometers, though, and I recall fixing one in a 70's Mercedes. They could easily be tested with a drill in reverse too.
So after getting together what information I could find, I went ahead and did the job on this one in my '86 560SL. Here's the step-by-step on this little, and very easy, project:

1. Usual first steps are to remove the instrument cluster and the speedometer unit. I'll skip the cluster removal as it varies by model, except to mention that the SL requires removal of the steering wheel first. The speedometer unit is then unscrewed from the back and removed from the cluster.

2.Remove the 4 screws holding the white casing and lift the casing off. To make working on the odometer easier (and safer, to avoid messing up the delicate speedometer needle), I supported the unit on the bench with foam pieces. You'll be working on the end with the gears.

3. You'll be able to see the damaged gear(s) at this point, probably very obvious. Mine had it's main drive gear missing (2 pieces later recovered from inside the body). To get at them, take out the 2 screws holding the clear lucite end-plate and lift it off (nothing will fly up or out, the gears won't drop out or anything).

4. As you can see, there was also a 'loose tooth' on the second gear down, which fell off as I rotated the gear with a screwdriver to count the teeth. You can move the large gears with your finger to check that the numbers roll over correctly and that there is no other damage to repair.

5. At this point, you need to determine a source for new gear(s), unless you have a donor parts odometer handy. I found several on the net, and decided on www.odometergears.com. Jeff, the owner, was very nice and helpful, emailed back several times, great telephone conversation, and just was excellent.

6. From the website, and from our discussion, I ordered the 3 gear package, even though I only needed the small drive gear and the second one down. The logic here is that the plastic is old and brittle, and it would be only a matter of time for the third one to pack up a tooth or 2. On the website, I went to the BMW section as the Mercedes pictures were down. Same VDO unit anyway.

...continued next post.....

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1986 560SL
2002 Toyota Camry
1993 Lexus