VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 1937/1938 Chevrolet 1/2 ton 3-speed transmissions

Hi Guys,

I know that the 1/2 ton truck transmission for 1937 was different from that used in cars (heavier gears, cut slightly differently; and thus one should not try to interchange individual gears from a car transmission with a truck transmission). I have a couple other questions in regard to this transmission:

1. Is the 38 truck three-speed interchangeable with the 37 three-speed? Are other years interchangeable with a 37?

2. Can you use a 37 or 38 three-speed from a car on a 37 1/2 ton?

I currently have a four-speed in my 37 1/2 ton and I'm contemplating some work on it in the future, which might include exchanging the four-speed for a three-speed.

Any help and advice greatly appreciated.

Thanks,

Jim

You can use a truck 3 speed in place of a truck 4 speed.(same length)
The car and truck three speeds are a different length.
The bell housing bolt pattern (for the trans) is different for trucks - so a 3 and 4 speed can interchange.
The 1937-1939 3 speed truck case is the same.
The 1937 main drive gear retainer must be used with the 1938 trans....due to the different throw-out bearings.

Gene,

Thank you very much; this is very helpful and I appreciate it!

Yours,

Jim

Gene
When I queried changing rear ends from a 4 speed into a 3 speed someone here on Chatter told me I would need to chage gearbox as well. While the overall length was the same the 4 speed had shorter driveshaft to allow for the longer gearbox.
I havent followed up on this yet but will need to at some stage.
Tony

"When I queried changing rear ends from a 4 speed into a 3 speed someone here on Chatter told me I would need to chage gearbox as well."
I'm not sure why this would be a requirement. In the 41-46 series trucks, the 3 speed used a smaller ujoint than the 4 speed. The splines are different for the 2 trans. The solution is to "split" the ujoint and have the 3 speed half of the ujoint up front, matched up to the 4 speed half toward the rear. If that makes any sense to you.

While its correct that the U joints are different the transmissions are the same length. It was not uncommon years ago to replace the 3 speed with a 4 speed for heavy duty use.

I have a 37 1/2 ton truck three speed transmission that has been rebuilt with gears out of a 47-54 transmission. Apparently all of the gears in those transmissions were the same in size throughout the 40's and into the 50's. It makes a nice transmission because the gears are angle cut gears. An older mechanic did it for me about 18 years ago. He use a 50's transmission he had to try the gears and when he found they would work, he found all but two new gears and used them in my transmission.

When my 37 had the original type trans I used a motors manuals 49 to 54 trans section for the directions to go through the 38 trans I was putting in and wish I knew the newer gears would go in too as I had a 47 trans in the shed.