Speedometer becoming slower and slower
 

The speedometer on my 1979 911sc has been gradually becoming less and less accurate with time (showing slower speed). At first it only became slow after about 70 mph, but, after a track event this weekend, it got worse. I don't think that it is the magnets, because of the progressive worsening. Any ideas?

Thanks,
Coglin

might be time to send it to north hollywood speedometer to be reconditioned. there is a signal check that can be done to make sure the sender and the magnets in the differential are working correctly. But i dont know how it's done.

N. Hollywood rebuilt my speedometer a few years ago and did a great job.

I would think about putting a very small drop of light machine oil on the bearing. My speedometer shows nothing below 25 mph, and I'm pretty sure it is just friction.

Try driving faster and faster.