check your condensers. They can fail intermittently with heat and some may be in the tach circuit.

How many condensers are there? There is the one for the alternator and that is the only one I can think of at the moment without digging thru the manual. Which I do not feel like doing after the day I've had. I know, no excuse

My original tach would "hang high" when it got hot in the car. 1976 280Z. Mid-summer, after a long drive, it just wouldn't come back down, it hung at around 2500 RPM, I think. After everything cooled, it went back to to normal. I got tired of it and swapped a 1978 tach in.

I don't really understand how these tachs work, so couldn't even guess on a cause.

Edited May 16, 201410 yr by Zed Head

There might be a transistor amplifier that drives the tach needle that might not be well stabilized against temperature variations. All I know about that is that one way for the designer to temperature stabilize a transistor amplifier is to put a resistor in series with the emitter of the transistor and ground. Maybe the designer selected the wrong resistor value or the resistor has changed in value with time, I have seen them change in old radio equipment. I wouldn't know what else to guess though.

How many condensers are there? There is the one for the alternator and that is the only one I can think of at the moment without digging thru the manual. Which I do not feel like doing after the day I've had. I know, no excuse

I can think of three, just from memory. The one on the alternator. Another is located near the voltage regulator, A/C relay under the metal bracket the fusable links are mounted on. The third is mounted on the coil and has two wires coming out of it.

I have seen a thread here from a member in Italy and he thought it had 6 or 7, but I can't find the thread right now. There could be more under the dash, need to dig through the manual to find out.

Chase

Okay, I have no idea what is going on. Unless it is heat related but the Tach is working fine! It is about 18 degrees cooler around here. Guess I'll have to wait til it gets hot again to trouble shoot it.

Glad that it's working, but you know the problem will come back, right?

Were you able to determine if it's a mechanical "needle sticking" or if it's an electrical problem?

Im going to say electrical. Each time I raised the rpms the needle would sometimes raise accordingly and then stick. When I came to a complete stop I could tap on the face of the tach and the needle would sometimes drop.

Oh...yes I know it will come back. I dont have any time to work on her right now. But when I do I will post what I find.