Ghost in my Speedometer? 1987 911

[iwhelan]

Hello,

Two separate times this has happened. I drive the car and notice the speedometer is not working. Even after a few stops and restarts, nothing. I tapped on the speedometer without result.

For what it is worth, when turning the key to accessory position to power up the electrics, I would see the speedometer needle do it's typical little jump, but then driving the car it would not move. Same with the odometer.

Both times (and these times have been separated by years!) I jacked up the rear end to start troubleshooting. I turn key to accessories, spin the right rear wheel, and it just works. Subsequent restarts and it's totally fine.

This particular time I even pulled the access panel in front of the rear seats so I could test the speedometer sensor with a multimeter and it works perfectly fine. 8 separate beeps from the continuity test. Prior to jacking the car up I even tried jiggling the wire connections in the access hole and that in itself did not solve the problem. I didn't pull the connection apart when testing. I just stuck the probes inside the connections to make contact.

The speedometer itself was repaired a few years ago because of a nonworking trip/odometer. I doubt any of the electronics were repaired because they weren't broken at the time, but just mentioning this just in case.

What could be going on here?

[Lyle O]

Check also the connections directly to the speedo in the dash. Use some De-Ox-it on them, or similar terminal cleaner. If this doesn’t work, it is likely something inside the speedo.

I had the same problem recently, so I hit the trip meter to check if the odo was working. Doing that broke the gear, so I sent it (speedo) in to Nichols Speedometer and Instrument in Greensboro, NC. They fixed the gear, and did a full diagnostic on the electronics. He said there were a couple of bad capacitors so those were replaced, all solder connections checked and cleaned, etc. Got it back, everything is perfect now. Big shout out to Nichols, by the way. Very reasonable price, and turn-around was just a few days. Great people.
Good luck.

[iwhelan]

Thanks, I guess I'll see if it happens again. Strange that it would be the connections since of how it hasn't happened during a drive, and then starts working again in an equally strange way. It's not intermittent, like you'd think would happen with a bad connection. Could be an internal issue as you said.