Had a 2.56 gear went to a 3.23. I had a 30's housing with a 37 tooth red speedo gear. Initial drive speedo was obviously reading a higher speed. So I needed a new speedo gear. With the thread browsing and calculations I went with a 43 tooth and new 40's housing..
Here's what I have now.
225 x60r 14
TH. 350
3.23 rear end
43 tooth speedo gear
GPS drive test
Speedo. GPS
20. 18
25. 22
30. 25
40. 36
50. 45
55. 48
60. 54
65. 57
I guess I could buy both the 44 and 45 and see which one is more accurate, however if someone has an exact match or suggestion I'm all ears or eyes in this case.
Mike

 

Maybe this will help

http://www.tciauto.com/tc/speedometer-gear-calculator/

or this

speedochartmarked_zps77437540.jpg

 

I got one of these for my car back in the '80s when I swapped form a 2.56 rear to a 3.55 rear:



Bought it over the phone from Ohio Valley Speedometer after giving them my odometer reading vs 5 mile markers on the highway so they could customize it for my speedo. It's very accurate. I was fortunate (and surprised) that it was within a couple percent after swapping to the current 3.23 gears and 245-60-14 tires.

 

Question: so I'm not just guessing on the drive gear teeth... ( the other gear 15-19) if you take the speedometer cable housing off and shine a light in there can you see the color of this gear to determine which one I have for sure? Didn't do this when I swapped driven gear from red to purple.... 37 to 43...

 

I also used one of these, mine was set on a dyno they got it within 1% at 60 MPH.

 

I used this company.

http://www.transmissioncenter.net/sp...n_______va.htm



I had to use a reducer, they had me drive my car with GPS at 40, 50, 60 mph. Called them, gave them my info they built my reducer, mailed it out that day, I installed it, and I now have a accurate speedo.

 

nevermind.

 

OP, what'd you end up doing?