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1977 280z rpm tach gets stuck

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scruz32

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Hello I have a 1977 280z and the RPM needle gets stuck from time to time. when I park the car and leave it off over night it will reset back to zero. This is my first post so I don't know if I am explaining myself correctly. I am looking for some guidance of what steps I should take first to check it without having to dismantle the dash. I know there has to be someone else that may have or had this problem. Thank you and I hope I am posting this correctly. Open to some feed back.

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Does the car run okay? Does the tach stick going both ways so that going to a higher RPM it still reads a lower RPM and when dropping off RPMs it stays reading too high? Just trying to understand better. From what I have read the tach can be taken out without dismantling the dash (harder with a dash cap). After turning off the motor does tapping the meter face cause it to drop to zero, which would indicate a mechanical failure instead of an electrical one? I would think replacing it would be a good road to take though I tend to be obsessive about fixing things even when replacement is easier (and sometimes cheaper!). I have never seen a circuit diagram of the inside of the tach though with that it might be possible to troubleshoot it if you have worked with circuits. Hopefully the mechanical bearings of the needle aren't sticking or it isn't binding to whatever coil drives the needle. If that is the case there might be a repair possible that would be similar to what is sometimes done with electrical meters to fix them. One suggestion I saw for electrical meters was to reduce the pressure on the bearings slightly in case they are binding. I did put ordinary light machine oil on the needle bearings on an electrical meter once and it started working but I think that stuff evaporates and gums up the works eventually. Anyone seen the inside of the tach meter movement? Does it just look like an ordinary meter as might be found in a VOM (volt ohm meter)?

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