I heard this trick on the speedo cable a while back, sometimes the square tang on the cable slips inside the square hole in the speedo gear so its not always spinning at the same rpms do to the slippage, they say you can slide a small piece of electrical shrink wrap on the tang and shrink it so it fits in the gear a little tighter if you feel its too sloppy. Pretty cheap to try and you can always cut it off if needed. Best of luck