Bouncing speedometer needle

[Stephen717]

Ok so whenever I have the gauges hooked up the tach and speedometer needles bounce. The tach was a N.O.S. sunpro super tach ii that my father had laying around and I'm guessing it's a bad ground issue. The speedometer on the other hand I'm not sure whether it's a cable issue or a gear issue. I just know it bounces constantly. Haven't been able to take it out lately as I've been busy with work but would anyone know if it's the cable needing to be lubed or if it's a bad speedo gear going from the trans to the speedometer cable and what size it'd be if I had to replace it. It's a Saginaw three speed and I'm pretty sure it's never been rebuilt