Dear bjcsc:

I was thinking about W116 300SD (1978-1980) and W126 300SD (1981-1985). I heard that W116 300SD has a mechanical speedometer and W126 300SD has an electrical speedometer. I believe that in both cases, the speedometer (mechanical or electrical) drives the odometer via gears.

For a LCD-based odometers, it's pretty sure that a tiny chip handles the calculations based on data from the speedometer.

Thanks again,

Eric