M-22 or M-21 ??
 

My build sheet says M-21 close ratio.. For sure it is a close ratio, but i thought it was just a 26 spline M-21 like the build sheet.. Someone tells me that it is a M-22 due to the larger housing and yoke ?? on the back of the tranny ???

Any ideas ?

The numbers on the case will identify it...

From 1971-74 ALL Muncies had 26 spline inputs and 32 spline out puts, M-20's, M-21's, and M-22's...

From 1963 1/2-70 All Muncies had 10 spline input, and 27 spline out puts, M-20's, M-21's, and M-22's...

In 1970 LS-6 Chevelles got M-22's with 26 spline inputs and 32 spline out puts, all other GM car used M-22's with 10 spline inputs, and 27 spline out puts...

And if your using the drain plug theory as only on M-22's, beginning in the 1970 model year till the end of production ALL muncie main cases were machined with both fill and drain plugs...

Hope this helps... Crash

There are three code letters on Muncie side case after date code

A wide ratio
B close
C M22 HD

^ that pretty much sums it up.

solarguy09: What year car? Casting number on main case? Stamped info from main case/midplate? This info will answer a lot of your questions and let you make use of the other pieces of info offered up in this thread.

Look for these kind of markings on the case:

P = Muncie
0 = 1970
A = January
21 = Day
B = M21

If you pull the side cover the different pitch of the gears will be evident. Also an M22 doesn't have any grooves on the input IIRC.

^^^ moot on the input grooves...... replacements have NONE either!!

I just went thru this a month ago.

^^ thats step 1.....still NOT 100%
very important visual comparison......when comparing PICTURES of the M-22 vs M-21 gears (yeah 30 deg vs about 22) you MUST compare the SAME GEAR!!!.....yeah laugh.....the 4th gear or maindrive gear on the INPUT shaft does NOT have the same helix angle as the other gears.

I say this because with the tranny together you cant really measure the angle on 4th gear but you can check 2nd gear.....guess what...2nd gear on a m-21 is within 2 degree helix of maindrive of a m-22......soooo....if you measure a picture of YOUR 2nd gear...and it is very very close to the maindrive gear (pics everywhere on the net)...it is a m-21

So...what do you think? Did GM mismark my case? :D

m-21

here ya go M-22

no your case is marked per m-21; however, it is quite possible and common to have a m-22 gearset in a case marked B.
As both the m-21 and the m-22 are exactly the same physical dimensions and use all the same accessories, it can and has been done many times. Considering this stuff is 40 yrs old...you gotta cover all the bases.

The sound of it is unmistakeable.

The only thing the "A", "B", "C", ratio code means is when trans left the Muncie assembly plant it started life as a M-20,M-21, or M-22...

Dimensionally and M-22 gears set will fit in any 1" cluster pin case...
And any 1" pin M-20 or M-21 gear set will fit in any other 1" pin case...

Hope this helps... Crash

its obvious the differnce in the teeth looking at the pic of the M22 cut thick squared teeth and the thinner angled M21 teeth. The M22 teeth have more strenght and make more racket.