Popped my cluster out today. The w124 is approximately the same as the w123 as far as the cluster attachment is concerned. The individual head-units are a little different, but nothing too difficult to figure out. Once I got the Spedometer/Odometer unit out of the cluster, I took to inspecting the gears. All intact. Using a small flat-head screwdriver, I clicked the trip odometer forward a little and got some movement on the main odometer. I looked at the drive mechanism, and the worm gear and drive gear were both fully intact.

After some confused muddling and tinkering, I determined that the main odometer axle had slid so that the drive gear no longer connected with the worm gear - and was not seated correctly on the opposite side (so that it was actually only attached on one end). I carefully re-aligned the axle with the port, and gently tapped the axle back into place, succesfully re-engaging the odometer drive gear with the worm gear. Re-integration to the instrument cluster was much faster - just assembling in reverse order from disassembly. A quick drive showed that the odometer was back in full working order. Total time: 45 minutes.

If I had to do it over again, I could do it in about 30. If I had known how simple it would wind up being, I would have done it on Monday when it stopped working in the first place (but I didn't want to have to spend the week driving without a spedometer if I screwed something up in the process).

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Lifetime owner
1977 240D

"new" owner
1988 300TE