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Discussion Starter · #1 · (Edited)
I recently acquired this Muncie and was wondering if someone could help identify if it is an M-20, -21, or -22. The fellow I bought it from got it for free years ago. He never installed it in anything and believes it to be a 1968 M-21, though he isn't totally sure. Can anyone help identify if this is an M-20, -21, or -22?

Here are some photos:














Thanks for any help you can provide.
 

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Build date Feb. 28, 1968.

First off, I'm far from an expert. The gear angles look like an M20 to me and the input shaft has two grooves which was used by the assembler for matching it to the cluster type. M20's had two rings. With the late '68 and models onward, they started stamping the type as the last letter on the build date line so it's a little easier to identify.
 

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The forward lever on the side cover is upside down. Pulling back on the shifter places the trans in 3rd gear instead of 4th gear.

Good purchase, even includes reverse back-up light switch.
 

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Discussion Starter · #4 · (Edited)
I've been searching Google, but I keep getting conflicting data. Some sources state the M-21s had two-grooves on the input shaft - other sources the reverse (while the M-22s had no grooves). I thought I read somewhere the teeth angles on the M-20 and M-21 were the same (some sources state 30 degree helix, others 45 degrees), is this correct? So far I know it musn't be an M-22 as the M-22s supposedly had no grooves on the input shaft, and their gears had 20 degree helices rather than the M-20/21 45 degree helices.

Can someone tell whether this is an M-20 or an M-21?

Thanks for all of your help so far!
 

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Google "muncie transmission identification yearone". I know Year One has a page that gives you the tooth counts so you should be able to mark one of the gears and rotate it while counting.

As for the grooves on the shafts, they did it different year to year. For '68 however, the M20 was supposedly the only one that could be had with two rings and got the two grooves to indicate it for the assembler. Now, that's not to say that someone hasn't swapped out the input shaft over the years. The best way is probably to count the teeth on first or second gear using that page from Year One.
 

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I've been searching Google, but I keep getting conflicting data. Some sources state the M-21s had two-grooves on the input shaft - other sources the reverse (while the M-22s had no grooves). I thought I read somewhere the teeth angles on the M-20 and M-21 were the same (some sources state 30 degree helix, others 45 degrees), is this correct? So far I know it musn't be an M-22 as the M-22s supposedly had no grooves on the input shaft, and their gears had 20 degree helices rather than the M-20/21 45 degree helices.

Can someone tell whether this is an M-20 or an M-21?

Thanks for all of your help so far!
Google "muncie transmission identification yearone". I know Year One has a page that gives you the tooth counts so you should be able to mark one of the gears and rotate it while counting.

As for the grooves on the shafts, they did it different year to year. For '68 however, the M20 was supposedly the only one that could be had with two rings and got the two grooves to indicate it for the assembler. Now, that's not to say that someone hasn't swapped out the input shaft over the years. The best way is probably to count the teeth on first or second gear using that page from Year One.
It is DEFINATLY a M20 with the 2.52 ratio with the 1" counter pin which was used from 1966-1970 with the 10 spline input and also to 1974 with the fine 26 spline input. The case stamping dates it as 1968, and for what it is worth counting the teeth on 1st & 2nd gear wont help as they are the same for M20 and M21 from 63-74. The difference between the 2 are the counter ( cluster) gear and the input. M21,s have 1 identification groove BTW.
 
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