Guys, what is the difference between the M22 and the M21? Is one better than the other, and why? Is the M22 a closer ratio, maybe more heavy duty?
Just wandering, a bud asked me and I said I have a great resource to find out. Thanks!!!

Rick, I'm not the expert on these here, DZauto is but here it goes. The M22 is the "rockcrusher" tranny. It's a bit more heavy duty than the M21 and much rarer. It's called a rockcrusher due to it straighter cut gears which whine ( and are stronger ). The M21 is a standard Muncie 4 speed. They both have the same ratios beginning with a 2.20 1st. The M20 is the "wide ratio" version which begins with a 2.52 1st gear. I know that the M20 came in cars with a standard rear axle ration ( 3.31 in my '67 ), while the M21 came in higher (numerical ) rear axle ratios. I'm not sure which cars the M22 came in but I would guess the 454 Chevellles and Vettes.

Thanks for the reply, now I know. I had a 70 (in 1971-73)with the LS5 and 4 speed. Bought it used, so I don't know if it had the M22 or not. I used to grind the hell out of third until I put a Hurst shifter in it, but it never failed me!

Rick, my Muncie ( I don't know what I have yet) whines in 3rd like crazy. Don't know why. As long as 2nd gear is solid. That's the weak one ( 'cause it gets hammered on).

I've also heard that they have different yokes. Is this true?

And, everyone above is right. The M20 is the wide ratio regular Muncie (2.56 in 63-65, then 66-74 it was 2.52), the M21 is the regular close ratio (2.20) and the M22 is the Heavy Duty (Rockcrusher 66-72, no documentation for a 73-74 M22).
AS A GENERAL RULE-there were exceptions, forget them, 63-70 Muncies had 10spline input shafts and 27spline outputs same as a p-glide or turbo 350. The 71-74 had fine 26spline inputs and the bigger output shaft same as a turbo 400 (70 M22 were like this, very rare).
Yes, the M22 is a whiner because of the different angle that the teeth are cut and they are considered stronger. The difference in a M22 is: input shaft, 1st, 2nd, 3rd, cluster and the reverse idler gears. EVERYTHING ELSE is the same and interchangeable. If you had a numbers matching 66 SS with a M20 and wanted a Rockcrusher, just buy these gears and stick them in your matching case(if you can find and afford them). I think this is all correct.


An after thought. If, just if you had a matching number 64-65 Chevelle (or anything) with a M20-21 amd wanted to convert to a really strong M22, it's too easy. First, break it all down to the bare case. Then send the case to Larry Fischer of L & D Transmissions in NY and have him bore the small cluster gear shaft holes to the larger 66-74 size and raise the hole centerline a few thousandths, to put the cluster closer to the mainshaft, install the above M22 gears and presto, an M22 in your matching number 65 SS. I've done it, it works.

I forgot to answer Gene. Third could have have some abnormal wear fore some reason. But I have found that frequently when only 1 gear gets replaced, either a new one or a used one, it will whine more because it has a different wear pattern than the original gear. Maybe in the past your 3rd got replaced, if so, it should not be a problem. Drive it and pretend you have a M22 when you are in 3rd.

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[This message has been edited by DZAUTO (edited 07-09-99).]

Amen.