Does anyone know how to tell an M-20 from an M-21? Any distinguishing characteristics between the two?. I am looking to purchase one for my 70RS Camaro and want an M-21, not an M-20. I want to be certain of what I'm looking at when I buy it. I know what to look for as far as gear wear, etc. but not on the differences between the two. Any help would be appreciated. Thanks a bunch!

As far as external markings, I believe the M-20 and M-21 both have studs on the shifter forks, the M-22 has tapped holes to attach the shift linkages. There might be some other, subtle differences, I'm not sure. I always stick a trans in first gear, and turn it over, while counting the output shaft 1 turn. The M-20 has a 2.52 first gear, and the M-21 has the 2.20 for first gear, along with the M-22. I used to have a catalog for Hurst shifters. It has some good info on identifying different transmissions, by side cover patterns and features.

Another thing I like to do with a 4-speed, is pull the side cover and inspect the clusters. Most sellers won't mind you pulling the cover, as long as 1) you are a serious buyer, and 2) they aren't trying to hide something, like chewed up syncros, or even worse, a chipped gear tooth or two. Also, ask why they are selling it. I regret selling my #'s matching M-20 from my 64 El Camino, years ago. I needed money, it was out of the car, well, dumb move. I doubt I'd ever sell another Muncie, especially if it was in good shape. Darren



[This message has been edited by Cameano (edited 11-17-98).]

The easy way is to look at the input shaft. There will be either none, one, or two rings around the circumfrence of the shaft. No rings indicate the possibility of the M22 HD close ratio, however, replacement input shafts also have no grooves, so beware. One groove would indicate M21 close ratio, two grooves indicate M20 wide ratio. The only way to positively identify a M22 rockcrusher is to remove the sidecover and look at the angle of the gear teeth. M20 and M21 are cut at an angle around 30 degrees, and the M22 are nearly straight.
As a side note, M20 wide ratio boxes were usually used with rear end ratios below 3.73, and M21 and M22 were used with 3.73 and above ratios. The exception being the 454 powered Chevelles which used M22's exclusively. With a smallblock, I prefer a wide ratio box, it is easier to get the car rolling.

[This message has been edited by Dave Birdwell (edited 11-17-98).]

Pull the sidecover and count the teeth on the input shaft gear. M-20 will have 21 teeth; M-21/22 will have 26.

Scooter,

Check out www.gearzone.net. They have a couple of pages on identifying Muncies. Pretty good reading.

Hey, thanks for all the responses guys, quite a bit of help. I talked to the guy selling it and he dropped it by my work today so I could check it over, and I didn't do anything with it yet, but did get some numbers off it. I will put another post in the Tag Team section for this info. I do appreciate all the info tho, and will check it out at work tomorrow. It does have two grooves on the input, so I'm suspecting an M20 at this point. He says he will exchange it for and M-21 until I'm satisfied, I guess he has quite a few of them, mostly from Corvettes. We'll see. Thanks again.