Finding Proper Speedo Gears

[LTZ C20]

Hey all, have a quick question here. New 700R4 in my 73 2wd 3/4 ton. Trans builder installed RED drive and driven gears for the speedo. Speedo doesn't read proper, go figure haha. I found a site with a calculator to determine which gears were needed, using tire size and rear end gear ratio.

Here's the calculator:
http://700r4.com/speedoCalc/speedocalc.shtml

Tire size is 265 / 75 R 16. Rear gear ratio is 4 : 10.

Then I found another site with a chart to find the right color depending on tooth number. Here it is:

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

Using the calc, it says my DRIVE gear should be a 19 tooth, my DRIVEN gear should be a 34 tooth.

Using the chart, the DRIVE gear should be YELLOW and the DRIVEN gear should be LIGHT GREEN.

Does this sound right? I think it is but want to be sure. Not taking it apart twice. Thanks guys.

[76LongBox]

To be honest, I have no idea if that sounds right or not, but I can tell you that the folks at TCI were very helpful to me with this same thing.  Last year I bought one of their TH350 transmissions for my '76 to mate up with a new GM Crate Engine.  My speedo was off after the swap, so I checked (as best I could) my rear axle ratio, and of course I knew my tire size.  I called them up and they told me exactly what I needed.  I ordered it, and it's pretty well dead on.

Someone else with more knowledge will hopefully chime in, but I just wanted to give TCI their props since you mentioned them above.

[LTZ C20]

Ok cool thanks. I will see about calling them next week and see what they say.

[Captkaos]

Based on the info you provided, that does sound correct...
http://73-87.com/7387garage/drivetrain/speedo.htm