After not being driven in over one month, I took my 82 380SL for some exercise. When I started the car, I heard a strange knocking sound that seemed to be from under the hood. I switched it off and checked around, but could not see anything unusual, so I tried starting again. When I got in the car, I noticed that the tach was on 1800 RPM. It started and ran fine, with no unusual noises or behavior. I did see the tach move above 1800 briefly, but after an upshift it just fell back to 1800 and stayed there.
I also have had a jumping fuel gauge for a long time, so I'm willing to spend some effort to remove the cluster if it is the gauge itself. Before I do, can someone tell me if the tach is driven off of the flywheel in this model, or is there some kind of amplifier under the hood that I need to check out, or perhaps there is a fuse?
Thanks for any advice.
David