These units are full of plastic gears [typical of bean counter work at VDO, I assume] and in the top photo you can see the END of one [of 2] bad plastic gears in this speedo. It is the white gear between the two spiral gears.
This is the speedometer out of the 78 EMS. All looks good here.
--literally--and the odometer stops odometering. I replace that gear--using a number of very special puller and pusher and holder tools--with a gear made of some modern, miracle plastic that is tough and won't slip on the shaft.
This photo shows the bad [cracked and slipping] small, white gear, the main register shaft, and just inside the speedometer frame, the bad [also slipping] part lead drive gear. I replaced both gears, lubed the unit, set the odometer to the figure the customer wanted, then reassembled it and calibrated the speed. Every speedometer has a specific gear ratio. The master VDO book [which I have] shows speeds for the speed needle, given various input speeds [from the speedometer cable]. I use a calibrated input speed, and set the speed needle to agree with the VDO figure for that speedo's gear ratio. No guess work. We all like the speedometer to read right. This one is ready for another 87,000 miles....