Last reviewed July 2026, maintained by Corvette-C3.com
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Look up a transmission code
Type the code off your gearbox, or a Muncie month letter. Chevrolet
reused these letters, so the lookup shows every model year a code was used in.
Where to find the stamp on each gearbox ↓
Every C3 left the factory with either a manual gearbox or one of Chevrolet's
automatics, and each carries its own stamped or riveted code. Read it and you can
confirm what the car was actually built with, which is the difference between a
matching car and one that has quietly been given a replacement box. The tables
below cover every model year from 1968 to 1982.
Where to look depends on which gearbox you have. On the Muncie four
speeds of 1968 to 1974 the stamp is on the passenger side of the case, on a
machined boss just ahead of the tailhousing. On the Borg-Warner Super T-10 that
replaced it the pad moved to the driver's side, high at the rear near the side
cover, so if you are feeling for it on the wrong side you will not find it. The
Turbo Hydra-Matic 400 carries a riveted tag on the passenger side above the pan
rail, plus a partial VIN stamped on the driver's side, the same convention used on
the engine block. On the Turbo Hydra-Matic 350 the tag sits on the right hand face
near the pan, and it is one of the most commonly missing identification points on
a C3, so do not assume the worst if yours has gone.
The Muncie month letters
The Muncie stamp is the best documented of the four and the easiest to read
once you know that the month is a letter, and that the alphabet skips eight letters along the way, F, G, I, J, L, N, O and Q:
A January
B February
C March
D April
E May
H June
K July
M August
P September
R October
S November
T December
From 1969 the Muncie stamp ends with a letter giving the ratio, and it is the
same letter you will find in the tables below: A for the wide ratio M20, B for the
close ratio M21, and C for the M22, the one everybody calls the Rock Crusher. That
last character on the case and the code in our table are the same thing.
We have deliberately not printed a worked example for the
Borg-Warner Super T-10 or the Turbo Hydra-Matic 350. The published descriptions of
those two disagree with each other on the order of the elements, and we would
rather leave a gap than print something that sends you looking for the wrong
character. If you have a clear photograph of either stamping on a car whose history
you know, the contact page is open.
