Speedometer is driving me crazy- Something is Wrong

AZ-Nick said

I disconnected the Speedo cable from the transmission and hooked into the drill and ran it at full rpm (1060) for 2 minutes on a stopwatch with my buddy watching the speedometer and odometer. The result was a steady 67-68mph and a total of 2.2 miles.
Now I am wondering about the gear inside the transmission

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At 1060 the odometer should read 2.12 miles. That you got 2.2 is close enough for horseshoes, hand grenades, and atomic bombs.

As for the 67 to 68 mph, that's a bit high 62 would be more like it at 1060.

1000/1060 is 6% fast, so 60mph at 1000 would be 63.6 at 1060.

So your needle is off by about 4mph.

With the correct gear you can make up for that or pull the cluster and adjust the needle.