M21 or M22?
#1
Advanced
Thread Starter
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.
#5
Team Owner
Member Since: Jun 2000
Location: Southbound
Posts: 38,928
Likes: 0
Received 1,468 Likes
on
1,247 Posts
Cruise-In II Veteran
#7
Le Mans Master
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.
#9
Dementer sole survivor
Member Since: Oct 2015
Location: YUPPY HELL Westford MASS
Posts: 16,432
Received 6,278 Likes
on
3,915 Posts
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
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.
Last edited by Rescue Rogers; 01-12-2019 at 07:52 AM.
#11
Drifting
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.
Check the 1st gear rotation as ascribed above. M20 is the more likely outcome.
#12
Safety Car
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...
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...
#13
Advanced
Thread Starter
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.
#15
Le Mans Master
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.