I have a 63 Dart, wheel size stock 13" and I just had a OD transmission from a 76 Aspen installed to replace the original 3 speed. Will the difference of wheel size and gear difference cause my speedometer to read 10 mph more than what I'm actually running? It seems to be the case, now how do I buy a speedo cable for this modification? I currently replaced the speedo cable with one for a 76 Aspen thinking that was the right choice, but like I said I have 13' wheels and I'm sure a 76 Aspen had larger wheels.
Can I just change the gear that drops into the transmission?
What would that gear count be in the A833?
Brian

Seeing that you are from L.A.. Check with Shannon at Redline Gauge Works...661-259-8891. He makes speedo cables and has all the gearing. He also has a Dyno if you want him to get it dead on. They are very Mopar friendly.

you should be able to take the drive gear out of the three spped and put it in the OD ....if you havent changed the rear gears or tire size should put you back with right reading on speedo....i
keep on roddin'

Nope. Speedo drive pinions in '63 were totally different from the ones used starting in '66.

It will not be hard to solve this problem. You will not need to spend money on custom cables or special adaptive ratio boxes. Just tell us what your rear axle ratio is, and what size your tires are, and we can direct you to the correct parts. If you are not sure how to check your rear axle ratio, see this post.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks to everyone for all the suggestions and assistance. I'm going to bump up wheel size to 14" first then do what I need to adjust the gear or install the correct one for what I'm running. I had a long conversation about tires with a collector for which he explained quality and strength or tires and how important and beneficial it is to have the right size and quality on the car.
Happy holidays to all,
Brian

Mmm...what sort of advice did you get from this collector? What'd he tell you?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I hope that you are not thinking that wheel size alone determines the pinion needed to drive your speedo correctly. You could put 20s on there
(though I wouldn't suggest it as it would ruin the looks of a great car)
and still have the same overall tire diameter that you have now, and therefore your speedo readings would still be correct. The transmission won't matter either other than the older/newer design pinion drive setup.