This is good news...kinda

[Eagleflyer]

The 1977 911S purchased last month has an unusual mechanical issue. At stop the speedo will show zero or 60 mph or some other speed and then go to zero. Very intermittent. While driving the trip and odometer rotate /count 10 times faster than actual. Example: driving from my house to the end of my driveway it shows I drove 1 mile when its more like 400 feet. The odometer shows 133K plus miles. If this has been going on for several years the car has a lot less miles than indicated. Questions:

What part is controlling the speedo?

With a 10 digit vin its a challenge to track down previous owners to better understand the actual mileage. Thinking of researching the 2 previous owners I can reach and keep going from there. Website someplace?

Thank you for your ideas on resolving this issues. Love the Car!

[Flat6pac]

Your counter is 8 magnets on a disc in the transmission, a problem of a dropped magnet your count would be slow. Your pickup may be faulty causing mis numerics, or the dash might be a problem with the count.
The least expensive is the pickup on the side of the trans, it connects to the harness in rear seat access in 2 individual plugs. Change the pickup and if problem persist, it’s in the dash
Bruce

[Eagleflyer]

Hi Bruce...thank you. I'll look into this

[Eagleflyer]

[Bill Douglas]

It could be an earth/ground issue.

It doesn't hurt to find all the grounds for the car and clean them. It can make lots of odd electrical gremlins go away.

[LIRS6]

Originally Posted by Eagleflyer

The lines of a true classic - it think’s it’s doing 70 when just standing still..