Transmission ID
Thread Starter
Racer
Joined: Mar 2011
Posts: 359
Likes: 13
From: Elma NY
Transmission ID
I am trying to ID my 4 speed, I think it is a M22 however they only installed ~ 80 in 1968. Casting # is 3925660 and date code is P8T12. Corvette is a 68 427/390 HP.
Thanks for any help Chuck
Thanks for any help Chuck
Drifting
Joined: Nov 2013
Posts: 1,548
Likes: 282
From: Scottsdale Arizona
There should be a letter after the number 12. I have a 68 similarly equipped and mine has the M20 wide ratio four speed. " A" is for the M20. "B" is for the close ratio M21 and "C" is for the M22. My guess would be yours is probably the M20. On mine the letter is difficult to see and required some cleaning.
Team Owner
Joined: Jun 2000
Posts: 38,923
Likes: 1,482
From: Southbound
Cruise-In II Veteran
Is your tranny original? Your VIN derivative will be stamped on it if it is. Was your car originally an L-88? For 1968, the M-22s were available only on the L-88 cars. You couldn't get the M-22 with a 390hp big block.
Last edited by Easy Mike; Apr 22, 2016 at 07:41 AM.
Thread Starter
Racer
Joined: Mar 2011
Posts: 359
Likes: 13
From: Elma NY
Trans ID
The trans has the vin stamped on it and it is right however it is an L-36.
Team Owner
Joined: Jun 2000
Posts: 38,923
Likes: 1,482
From: Southbound
Cruise-In II Veteran
Safety Car
Joined: Sep 2007
Posts: 4,458
Likes: 331
From: Indy Indiana
it was not until the model year 1969 that the A, B, or C was always stamped as a suffix to the assembly date code. before that, some did and some did not. since it is pretty sure you don't have a M22, and the maincase and extension housings were the same, you will just have to count the teeth in the gears to see what you have.. in 1968, the M20 and M21 were about 50-50.
if 1st gear seems to lug.. then you may have a M21... due to the higher ( lower numerically) gear.
if 1st gear seems to lug.. then you may have a M21... due to the higher ( lower numerically) gear.
Thread Starter
Racer
Joined: Mar 2011
Posts: 359
Likes: 13
From: Elma NY
Trans
it was not until the model year 1969 that the A, B, or C was always stamped as a suffix to the assembly date code. before that, some did and some did not. since it is pretty sure you don't have a M22, and the maincase and extension housings were the same, you will just have to count the teeth in the gears to see what you have.. in 1968, the M20 and M21 were about 50-50.
if 1st gear seems to lug.. then you may have a M21... due to the higher ( lower numerically) gear.
if 1st gear seems to lug.. then you may have a M21... due to the higher ( lower numerically) gear.
