My 79 sport coupe has the deluxe instruments option. The tachometer has been reading steily higher over about the last ten years. It now shows an idle of 2000rpm, and at 65mph it is 7000rpm. The voltage is reading higher than normal also even though the lights and such look normal.

Obviously I'm not turnoing that kind of rpms, and this is a 4 speed manual. (Semi-stock Engine would probably explode if it was 7000rpm anyway)

I did remove the tach to see if there were any adjustments, and there aren't. I really can't afford the mega-buck replacement cluster or rebuild. And I dont want to hang an aftermarket item on this dash which is in mint condition.

Does anyone know of a proven trick or mod to correct this? I already tried putting a variable resistor in the distributor tach feed, that doesn't work.

Any one else having this problem on an older car?