I have a Th400 Tranny 323 posi rear and super stock II rims 14 inch and a 455ci motor what would be the correct number of teeth for the tranny thanks.

 

Do you have a copy of the factory service manual? There is a chart for the drive and driven gear.

 

YES i DO BUT iM NOT SURE OF THE PAGE

 

Here ya go.

misc.jpg

 

so if my tires are 245/60 R14 what color is the tooth I would need

 

According to what I found that's equivalent to an H78/14 so use that as a guide line.
Also you need to make sure you have both the correct drive and driven gears in the trans.
So that would be 18 & 43.

 

I have a 72 with a 350 turbo automatic. My new rearend has 3:73 ratio and I have 15 inch rims. Any ideas on getting this close?

 

If your tires are different than the chart you could ratio your new tire circumference to the tire circumference on the chart. Say for example your actual circumference is 5% more. I kind of called this my "correction factor".

This is assuming gear ratio between what you have and what is on the chart is the same. If your gear ratio is also different the same idea would work but you have to ratio for gear too.

Than take the ratio of driven and drive gear per the intended tire size on the chart and bump that ratio by 5%. This was my "magic number"

Use the chart to find any combination of drive gear driven gear ratio that is close to your magic number.

The drive and driven gear you now select may not make any sense per the chart based on what is says for tire size and gear ratio , its all about picking the right ratio (magic number).

Thats how i did it for my 3:90s without using one of those adapters. For comparison i believe at 40 mph my speedo was off by 1 or 2 mph. I couldnt get it exact but it was close enough.

When i did mine i had this whole sheet of math calculations that i never saved. I wished i saved it because it would be easier to show the formulas than just try to describe it. I wish i just put it into an excel sheet so all i had to do was plug in a number.