64 - 66 Chevy C10 Speedometer Problem
 

I have a 1965 Chevy C-10 pickup and when the odometer went to rollover to 600 miles, it hung up at 599.9 and the speedometer started to click back and forth in a 10 mile increment. I found a used unit and when I put it in, it ran good until in tried to rollover to 800 miles and hung up at 799.9 and the speedometer started to do the same thing. The first one was at 73000 and the second was at 48000. Also, does anyone know a company that revamps these clusters or sells rebuilt ones. Looking for some help.