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Discussion Starter #1
Have a dilema. Selling my M21 but have been told its a M20. Casting comes back as 69 but input has 2 grooves. But when it was in the car behind the 454 i had a 3.00 diff and i could get over 50mph first gear.. M21 is a 2.20 first gear i assume. M20 is 2.52.... Help appreciated
 

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Input Shaft Output Shaft
Year Type Rings Splines Tooth Count Splines
1963-1965 M20 None 10 24 27
1966-1970 M20 Two 10 21 27
1970-1974 M20 Two 26 21 32
1963-1970 M21 One 10 26 27
1970-1974 M21 One 26 26 32
1967-1970 M22 None 10 26 27
1969-1974 M22 None 26 26 3

I always was told that my 67 Nova had an M21...then I pulled the trans and saw the two groves. M20. Hope this helps some.

Dave
 

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Discussion Starter #3
I guess i can't confirm 100% diff gears so between a 2.2 and 2.52 first gear you wouldn't notice that much especially behind the big block.. Definitely does have 2 grooves in front... Some say M20 are stronger and others swear by M21. Either way it's for sale so weather one commands more or less money i don't know. Just want to sell it..
 

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Put it in 1st gear and turn the output shaft exactly one revolution.Input will turn 2.2 or 2.5 revs.If it's still in the car,you can turn the motor instead and see how many revolutions it takes to turn the driveshaft one rev.
 

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Tell them you were told it came out of a COPO car and put $2500 on it, they'll be burning up the highways and beating down your doors to buy it. lOL
 

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Put it in first gear and spin the input while count the output.
 
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