Do the Motorsport speedos have a mechanism to match your odometer? People are awfully sensitive on any discussion about changing odometers so I am curious how you matched them up.
Do you just connect a drill to the speedo and spin forever?
The drill takes waaaaaaay too long. I have a spare 85MPH speedo that I put a drill on. Even at max speed, it takes a good 30-45 seconds for 1 mile to turn over. You'll be there all day. It might be good if you need to spin off 10 miles, but not 20,000.
You also cannot spin them backwards. Only forward. Theres a 1-way clutch on the odometer that prevents them from running back.
The motorsport speedos actually ship with instructions on how to match up the miles. I have found a picture of this doc, but unfortunately the quality was so bad I couldn't read it.
How I do it is to flip the speedo over and look at the odometer from the rear. There's a small rod with white gears on it that advance the miles. If you tap one side of the rod out, you can lift the rod and spin the odometer to where you need it. Then you can reset the white teeth. The white teeth have teeth of different sizes. One big, one small. The big tooth fits into a large slot on the odometer which moves the digit up one spot. It doesn't nececcarily make it difficult, but if you study how the teeth fit in, you'll see how they much sit once you are ready to replace the rod.
As for legality, my understanding is that it's only illegal if it's done with the intention of deception. If you are replacing the speedometer and, in good faith, are matching up the mileage, then it's not illegal. However, I haven't read the law nor am I a lawyer so don't go based on that. But in 2021, many of these cars have odometer discrepancies anyway, and in many states it doesn't matter.
Like I said previously, I thought about doing a how-to, but people get weird when you bring up rolling back an odometer, so i'm not going to go there.
However, If someone can find the Ford motorsport directions to correct the odometer, i'd love to read those