Speedometer bounces all over the place

Mine does the same thing. clicks under 30mph or so and around 65mph its bouncing between 55 and 70. Guess it's one of those fancy "approximate" speedos (lol). In all seriousness my duster's cable did the same thing, one day my cousin took the cable loose at one end, and said it had twisted itself (probably from topping out the speedo), and he claims he just twisted it back and that fixed the issue. Granted, I wasn't present when any of that happened, but it did fix the jumping around. Still clicks at low speed but that could be the plastic gear too.