I believe you need the 21 tooth (don’t know the color), I can’t remember what is in mine but I have 3.73:1 and it is a corrected gear. It's fairly close to accurate. Call up Max at 5 star Ford, he will know for sure what you need. You only need to lift the driver’s side of the car up and take one bolt out like they said, easy stuff.
"Ford speedometer driven gears for automatic transmissions. AOD transmissions use either a 7 or 8 tooth drive gear. Once you change the gears in your differential or tire size, you need a new speedometer driven gear to recalibrate your speedometer. They're inexpensive and only take a few minutes to change. We have 16, 17, 18, 19, 20 and 21 tooth gears. The 16 tooth gears have longer teeth because they fit more than one application.
23 tooth Ford speedometer driven gears for use with 4.10 gears with 7 tooth shafts in automatic transmissions."
Info from
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