Tachometer??

[scoutll]

I know this is an electrical issue, but was hoping someone has had it before and can help me cut out some gremlin chasing.
The tach on my 63 is reading about 500 rpm high. When you turn the ignition on (without starting the car) the needle instantly jumps to 500 and stays there. When the car starts, it continues to read that 500 rpm to high ie... the car idles at 800, but the tach is reading about 1300. The needle also flickers up and down slightly when you are driving.
This is the original tach and it never did this before, just started a few days ago....

 

[spritenut]

If it's 500 too high with just the switch on, just re-zero the needle.
Remove the glass and the back housing, hold the flywheel still with your fingers and move the needle back to zero.
The potentiometers also absorb moisture over the years and will throw off the readings, they are adjustable, just turn the little wheel screw.
I am not sure about a 63, but 65-67 had this.
Hook up a known good tach to the coil and adjust yours to suit.

 

[scoutll]

Thanks. I was wondering if anyone may have had this happen to theirs, and wondering why it might suddenly start doing it.

 

[Sarastro]

My guess is that one of the capacitors in the circuit has become leaky. They deteriorate over time. If the tach indicated 500 RPM with no power, then it would probably be the needle. But, rezeroing the needle as a quick fix is probably a reasonable thing to do anyway.

It's likely, though, that it's not accurate over the full range. So be careful not to trust it too much and over-rev. Meanwhile, it might be good either to start looking for a replacement--they're cheap on ebay--or get someone to rebuild the internal electronics and recalibrate it. This should be easy for any electronically knowledgeable person.