Back about twenty years ago, had trouble with the big speedo gear inside my T10. Original was grooved and any replacement long gone. Used one of similar tooth count, same outside, but one that had hole in center too big. It was designed for yet some other tranny. I then had a friend make up an aluminum collar. We shrunk fit this into the gear and then onto the output shaft.

The replacement gear may be out there now, but this one has worked good ever since.

Wm.

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Old Ford owner