tachometer sticking... sometimes works normally
 

the tachometer in my '85 911 is sticking. it sometimes sticks showing at idle while im driving, then sometimes shows the wrong RPMS and fluctuates. Today while driving it showed 1000 RPM and then after hitting a bump it normalized to 3500RPM, .... something Loose? where do I begin to look? Thanks

Sometimes the “glass” can get too hot and flex against the needle causing it to stick- mine will do this if it sits in the hot sun. After it cools off a bit, needle flys up to the correct reading.

Interesting
 

The car is parked underground and it is now cold in the NE. Don’t think heat has affected the tachometer. Thanks

Mine was acting up and would just drop to zero, and start working intermittently. It also seemed to have something to do with going over bumps. My mechanic sent it to Palo Alto Speedometer for repair and it’s perfect now.