calibrating speedometer

i have a 904 trans. my car had a 7 1/4 with 2.76 gears. i recently upgraded it to a 8 1/4 with 3.21 gears.

my problem is that my speedometer is off now. does anybody know how i calibrate the speedometer so that it is at least close?

my tires are 26.6 inches tall.

thanks

You may just need to change the nylon (or is it metal) gear in your trans with one with less/more teeth. You will just need to calculate which one you need.

I just bought a new speedo gear for my Scamp and it arrived in the mail today. Funny thing is that I bought it from Southey Motors Ltd (just north of Regina) as they were one of the only ones in Western Canada that had the right gear. If you call that dealer, talk to Allan in parts, he's restoring a 70 Dart with a 340 right now. He had one of the rare Canadian only '71 340 Darts a few years ago.

I went from a 7 1/4 2.76 gears to an 8 1/4 with 3.21 (although when I divide the # of teeth on the pinon with the # of teeth on the ring gear, it's 3.23) gears. I will be running 225/60/14 (24.6" diameter) on the rear so I went with a 34 tooth gear. Use this website (and open the xls chart) to determine which one you need.
http://www.moparts.org/Tech/tech/pages/speedo.html

Do you need to contact a dealer to get one of these? i looked at year one and paddock and could not find any of them?

Thanks,

Steve