Harley Transmission Serial Numbers

There is no breakdown for the transmission number and the primary has no numbers. If you could give me the engine number I will give you the correct.

For Big Twin transmissions 1936-1964 there are 4 types of transmissions cases that were used: Type 1: 1936 - identified by only having the 4 mounting studs holding the transmission to the frame. The 5th mounting hole located under the kick starter does not exist on these transmissions. Additionally, there is no boss for this 5th mounting point cast into the transmission case. I believe a bracket was used between the kicker cover studs and the frame in 1936. Additionally, this case has no vent boss cast into it. The vent boss is normally located on top of the case just forward of center on the kicker side.

During these years the transmission vent was located on the kicker cover. Type 2: 1937-1939 - identified by having no vent boss cast into the transmission case. The vent boss is normally located on top of the case just forward of center on the kicker side. During these years the transmission vent was located on the kicker cover. Five mount points on all cases 1937 and later.

Type 3: 1940-1955 - The transmission vent has now been relocated from the kicker cover to the transmission case. There is a vent boss cast into the top of the case just forward of center on the kicker side.

It is drilled and tapped for a vent screw (not one of the screws that holds the transmission top in place). Corel drawing tutorials. Type 4: 1956-1964 - The transmission vent boss is still cast into the case (top of case, forward of center on the kicker side) but it is no longer drilled and tapped for a vent screw.

The venting is not achieved using one of the screws that secure the transmission top. The transmission in the ebay ad is a Type 3. You can clearly see the vent boss cast into the case next to the kicker cover in several photos.

With some more investigation (pull the kicker cover, study the shape of the kicker arm) you might be able to determine if the 'GO' means July-1940 or July-1950. Hi: Thanks for the explanation, however I am still confused. I can tell how you identify the catagory of year the trans falls into, but how do you identify a 4 speed vs a 3 speed? I have the same looking trans as the one from the ebay, item. Same numbers 121-35 and the 2 up to the right. My tag says J6.

So that's October of what year? If it's a type 3 then it would have to be 1946 because that catagory goes from '40-'55. Looking into the gearbox, what is the difference between the 3 speed and 4 speed because the numbers don't tell you that.

Thanks for all the help. I am so confused.