'83 240D. The speedometer works fine, needle holds steady at any speed. The odometer doesn't work. When I zero the trip odometer it and the main odometer will work for a few miles, but then they stop working until I zero the trip odometer again.

Any ideas what's wrong and how to fix it?

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'75 John Deere 450C (times 2)
'83 240D plus parts car
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