Trying to determine what tooth speedo drive gear would be in a 71 m20, factory 3.23 if that matters.

 

When I was looking for a speedo gear I reached out to Autogear, told them all the specs (tranny type, rear end ratio, tire size) and they sent me the correct speedo gear. It's within 2 mph @ 60 mph

http://www.autogear.net

I know there are also calculators on line to figure it out yourself

 

I need to determine the drive gear count 7-8 or 9 to get to my driven gear. If it's an 8 tooth then I need a 21 for my gearing and tire size.

 

So conformed with Paul @ 5speeds.com that it is an 8 tooth drive gear. Good guy for parts and info.

 

He's got some great rebuilding videos as well. I need a rebuild kit for my Mustang's T5 but unfortunately he's out of stock and apparently has been for a couple years. Maybe he's sticking to Muncie's and T56's now

 

There is a speedo gear chart on TCI page that will help determine what gear you need. You need to know the tire diameter, and either the drive or driven gear tooth count. Enter those figures, it will calculate the other needed gear.

 

Well, crap. It just occurred to me your working with a manual trans. TCI doesn’t list gears for a M20. The formula would be the same, so you determine the correct needed gear. I’m not sure if the gears are the same between auto and manual trans.

 

I think there is a chart in the 1965 Service Manual that shows the different size gears, not sure if 71 Manuals have it.

 

There is a chart in the service manual. Biggest hassle using that chart is converting the old tire size to the new methods.

 

275-60-15, 3.73 gears, 8 tooth drive gear takes a 21 tooth driven.