Pulled the transmission out of my car. Want to know if it's a M21 or M22. How can this be determined? It is matching numbers to my car. Thanks for any help.

 

The M22 should have fragments of rocks nearby...lol.


Seriously though, is it listed on the body tag? I am going to plead ignorance, as I don't know if they did that with 68-72s. I know that for some 73s with 4 speeds, I have seen it stamped on the body tag.


From what I recall, the M21 had helical cut gears, where the M22 had straight cut gears, which helped dissipate heat better, but made more noise, hence giving it the Rock Crusher nickname. The M22 also apparently had a higher nickel content.


I'd be nice if there were just a big stamp on the side of the thing though...

 

The '72 service manual only shows a 3spd & a M20 4 spd on the trans ID chart. The '71 manual does list both the M20 & M22. If I remember the M22 should have the larger 32 spline output shaft like a turbo 400. Also the M22s at least the later ones had a fine spline input shaft not the 10 spline input shaft that most muncies had. If you can still see them there should be letter codes painted on the pass side of your case. "WT" is the only one listed for a 72 4spd,(M20). The '71 M22 used a "WO" code.

 

Thank you both. Will take this information & see if it's the answer.

 

69-74 On the assm date stamp on the trans.(Ex P4D23B) The last letter designates M21, M20, Or M22. A=M20 B=M21 C=M22

In the ex above: P4D23B
P=Muncie
4=Year 1974
D= April
23=23rd day
B=M21

 

M-20 was the only 4 speed trans offered in 72. This chart is from the 72 inspectors guide. Originally the trans would have a metal tag with part number and code embossed on it.

Don W

 

Example of trans tag.

Don W

 

The trans should have the last 8 digits of the VIN stamped on the left side of housing.

Don W