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Discussion Starter #1
Hey guys, (and gals.)

Please help me out of a jam.

I need some digital imagery sent to my email account. Help. Help. Help.

I need photos that show the difference between the Muncie M20 and the Muncie M-21, in detail!!!

Photos of both if possible. Help.


69 RS-SS




[This message has been edited by Scoop69RS-SS (edited 11-06-2001).]
 

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I hope that i read your post correctly. The outside will look the same. It's the gears inside that make them M-20, M-21, M-22. The only other thing is the stamping on the outside of the case by the assembly date. A=M20, B=M21, C=M22. The ABC stamping, however, was only started mid-run for 1969.

You could get pics of the shafts. Those look different. Jerry MacNeish's The definitive Z28 and SS-396 book has pics.

[This message has been edited by Silver69 (edited 11-06-2001).]

[This message has been edited by Silver69 (edited 11-06-2001).]
 

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Discussion Starter #3
Yup, you're reading me right. Thanks.

Can you get me copies of the two different input shafts?

[email protected]
 

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The M-20 has 2 grooves on the input shaft and the M-21 has only one. There is still no guarantee on what the trans is though without counting the teeth on the inside unless it is a later model with a letter code on the casting. Of course someone could have still swapped the guts into one of these but is probably unlikely.
 

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Also, the M22 has a 1" countergear pin. The M21 and M20 used 7/8".

The book Chevrolet by the numbers, by Alan L. Colvin has an appendix in the back of the book about the "Rockcrusher". Hope this helps.
 

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Actually since 1966 the M-20 and M-21 also carried the 1" countergear pin. The only true way to tell is to count the teeth. the M-20 (1963-65) input shaft teeth on the gear (not splines) was 24 teeth. The countergear shaft teeth were 17, 19, 22 and 29. 1966-74 was 21 on the input and 17,19,22 and 25 on the countergear. The M-21 was 26 teeth on the input 17,19,22,27 on the countergear. The M-22 had the same teeth count as the M-21 but the helix angle of the gears is different. Hope this helps
 

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You can put the trans in first gear and rotate the tailshaft 1 revoluton while counting the number of revolutions on the input shaft. This will give you the approximate first gear. Match this up with the first gear for either the M-20 or M-21/22. I know the M-20 has a lower first and I think it is aroung 2.5 vs 2.2 for the M-21/22. If you think it is the M21/22 you can take the side cover off to verify if the gears are straight cut.

Kent
 
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