So I recently bought a '68 'Bird - original 400 car, but now has a chebbie 427. Trying to figure out what tranny she has - feels like a close ratio when I drive it (not much rpm drop b/w shifts), but that's the extent of my knowledge on the subject. Is there any way to look at the outside of the tranny and tell which one it is?

Thanks!

Scott

Hey Scott,
This should do it for you.

http://www.5speeds.com/muncie2.htm

Jim

Hey, Jim, thanks for the link - great info there. Based on what I read, the casting number is from an M20, M21, or M22 from 1968-1970, so it could be the original trans.

And it sure feels like a close ratio trans - not much of a drop in rpm b/w shifts - so that would narrow it down to an M21 or M22 - but it appears that there is no way to tell difference b/w M21 and M22 without taking it apart (angle of gears is different) unless you can hear distinct gear whine while driving. Well, I have a huge gear whine, but it's coming from under the hood - am about 99% sure that my engine has a gear drive - it's LOUD!

So, some of the mystery is solved, but not all of it...

Thanks!

Scott

Drove it again today and tried to tune out the whine from under the hood and listen to the whine of the tranny. Tranny whine was very noticeable, even above loud gear drive and leaky exhaust, so I'm thinking it might be an M22...

You could do some fancy math calculations using the rpm and the mph in each gear to determine the ratio. If you don't get into calculations you could give me the mph and the rpm in each gear and I may be able to make an educated guess. Without taking out the trans and counting the spline and the rings I can't think of another way to tell.
Jim

Take off the side cover and look at the gear set. A 20° helix is an M22 and a 45° helix is an M21.