Tach Question- Not reading correctly

[PatS]

I need some advise. I have '70 SRL and have a tach that is acting very odd. At idle or low RPMs, nothing registers and then once I get able 1,000 RPM is starts. I used my timing light that has a built in tach and noticed a ~700 PRM difference. The tach cable is fine adn is not broken. I disconnected it from the tach and watched it spin. It seems to be turning very slowly. I am hoping it's not a distubtor 'gearing' issue but...

Thoughts?

Thanks

[JT68]

Sounds like the tach is dorked up or one of the gears in the distributor base is slipping. Easiest way to test is hook up another tach. If it does the same thing its the gear, if the new tach reads correctly, it was the tach.

If you need a tach for testing, we have plenty//

[PatS]

Good idea Jim. I have a one with Jon F right now being refurbed. I try that when it returns.