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M21 or M22?
Any idea which transmission this is? This was in my 1972 LT1. I recently had to pull the motor and thought I would take a pic of the I.D. to see what transmission I have. The only issue is the stamping isn’t very clear. I apologize this is the only pic I got from the mechanic before it got reinstalled. Let me know your thoughts. It’s definately not an “A”. Thank you for your opinions/info. https://cimg1.ibsrv.net/gimg/www.cor...0515db13f.jpeg |
It looks like the stamp on my 68 M20. P means Muncie followed by K meaning July and then the date. The derivative VIN is from a July 68 Corvette. |
It’s the last letter that I can’t determine. Any idea if it’s a bad stamped b or a c? It appears to be lower case. |
From what I’ve read 68 Muncies weren’t stamped with a letter after the date code indicating if it was a M20, 21 or 22.
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Originally Posted by sullyman56
(Post 1598664061)
...From what I’ve read 68 Muncies weren’t stamped with a letter after the date code indicating if it was a M20, 21 or 22...
:thumbs: |
There were only 27004 72's made. This is out of car #27481. I agree--looks like a 68 stamping.
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Raise rear wheels....put car in 1st gear.....put mark on drive shaft...rotate engine exactly 1 revolution...check mark on drive shaft to see how far it rotated....if driveshaft rotated slightly more than 2.5 times around it is a M-20....if it rotated slightly less than 2 and a quarter turns, it is an M-21.
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That character after the date code is an inspection mark. Sorry, not a "C".
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Originally Posted by stingr69
(Post 1598664869)
Raise rear wheels....put car in 1st gear.....put mark on drive shaft...rotate engine exactly 1 revolution...check mark on drive shaft to see how far it rotated....if driveshaft rotated slightly more than 2.5 times around it is a M-20....if it rotated slightly less than 2 and a quarter turns, it is an M-21.
As a bonus, if you arent the original owner and the previous owner has had it rebuilt, it could be any number of things inside there. I just changed my gearing from M21 to M20, it was just the input shaft and the idler gears, easy swap. You can also now buy wide ratio and close ratio aftermarket M22 gears so you have that posibility as well. |
Don't M22's have a drain plug and 20's and 21's do not?
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In my limited experience, many who say they have a "Rock Crusher", don't. It is a fairly rare transmission. Like 4-speed C3's being wrapped around trees and plunged into ditches at a far greater rate than the automatics.
Check the 1st gear rotation as ascribed above. M20 is the more likely outcome. |
no, 70 and newer muncies all have drain plugs, 69 and older do not have drain plugs.. doesn't matter if they are m20, 21, or 22
most people that think they have a factory m22, do not... it is a rare tranny. i bought a car from a kid once who swore it was a m22 due to the gear whine... i knew it wasn't .. it was dry of oil.. that was the gear whine... |
Originally Posted by stingr69
(Post 1598664869)
Raise rear wheels....put car in 1st gear.....put mark on drive shaft...rotate engine exactly 1 revolution...check mark on drive shaft to see how far it rotated....if driveshaft rotated slightly more than 2.5 times around it is a M-20....if it rotated slightly less than 2 and a quarter turns, it is an M-21.
Thank you everyone for your responses. |
Actually isn't it the other way around?
rotate the engine 2.2 or 2.52 times to get one revolution of the driveshaft... in 1st gear? my brain hurts... |
Originally Posted by joewill
(Post 1598682438)
Actually isn't it the other way around?
rotate the engine 2.2 or 2.52 times to get one revolution of the driveshaft... in 1st gear? my brain hurts... Good catch - Count ENGINE ROTATIONS per one rotation of the driveshaft. Close ratio M21 Muncie is 2.2:1 ratio and wide ratio M-20 Muncie is 2.52:1 M-22 is close ratio as well. |
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