How to Read Transmission Year ID Codes: Location and Decoding Guide
Where to Find Transmission Year ID Numbers
The easiest place to start looking is on the bottom of the transmission on the kicker side (passenger side). You’ll be looking for a raised boss or casting surface that has numbers and letters stamped or cast into it. This location is standard across most American transmissions, including Harley-Davidsons, Chevrolets, Fords, and other manufacturers.
Near the casting part number on this boss, you should find a letter and number combination. This is your date code—it tells you the month and year the transmission was manufactured.
Decoding the Letter and Number Format
The most common format for transmission date codes is straightforward: a letter represents the month, and one or more numbers represent the day and year.
- Letter: Month of manufacture (A = January, B = February, C = March, and so on through the alphabet)
- Numbers: Usually the day of the month and the last digit of the year
For example, if you see “B 15 7” cast into the case, it means February 15, 1967 (or possibly 1957, depending on when the transmission was made).
Early vs. Later Transmission Codes
Not all transmissions use the same system. Older transmissions, particularly those from the 1930s through 1950s, use the letter-number format described above on the kicker side. However, transmissions made in the 1960s and later may use different coding systems depending on the manufacturer.
Harley-Davidson transmissions made from 1962 onward, for instance, shifted the location of ID codes. Instead of the kicker side, these codes appear just below the ratchet lid gasket on the top right front side of the case. The letters used changed by year (A for 1962, A or B for 1963, B or C for 1964, and continuing through the alphabet, with double letters starting in 1979).
GM Transmissions and Other Manufacturers
General Motors used a slightly different approach. Pre-1967 GM transmissions included the plant prefix, production date in numerical form, and a shift code (D for day shift, N for night shift). After 1967, they switched to a new system with transmission type, coded date, and shift code.
Ford and other manufacturers each have their own variations. The month code for some manufacturers does not follow simple alphabetical order—for instance, some use letters like H for June, K for July, M for August, P for September, R for October, S for November, and T for December to avoid confusion with other manufacturing codes.
The Challenge: Determining the Decade
The main limitation of these simple date codes is that the year is represented by only the last digit. A code showing “7” could mean 1937, 1947, 1957, 1967, or 1977. To narrow this down, you need additional context: the transmission type, any casting numbers, the vehicle it came from, or any related documentation. Comparing the transmission to known examples of that model from specific years can help confirm the decade.
What to Do Once You Have the Code
Once you’ve found and read the date code, write down the exact letter and number combination. If the casting is hard to read, take a photo with good lighting or rubbing the surface gently with chalk can help the raised numbers stand out. Then cross-reference your code with the transmission type and any other identifying information to pinpoint the year and verify its authenticity or originality in your vehicle.