E21 Speedo Working but Mileometer Not Recording?

[Steve21]

Recently my mileometer stopped working although the speedometer was still recording the road speed correctly. This had happened before a few years ago and having taken the speedo out of the instrument cluster I had noticed that a plastic gear had developed a crack in it and was loose on its shaft. Being loose it was not transfering drive to the mileometer or tripmeter and therefore although the cable was driving the speedometer the mileometer was not recording mileage. On removing the speedometer I found the same fault had developed again - look out for this if you find this fault developes with your mileometer. See the image below to help identify the suspect.

[uwbuurman]

Save a lot of miles on the car!

[PeteK]

Did you have to get a complete new speedo, or just replace the gear?

[Steve21]

I replace the gear. I had another speedo that on close examination also had the hairline crack in the same gear although the gear was still intact - just. The gear can be slid off the shaft - it appears to be just a friction fit. Once off the shaft I introduced some superglue into the hairline crack and once refitted on the shaft I added the tinyiest bit of superglue to stop it rotating/slipping on the shaft and it worked a treat. The drive was restored to the mileometer and tripmeter.