VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 '37 1/2T transmission swap

Considering putting a '41 4 speed transmission in a '37 1/2T.

It appears that the universal joint from the '37 will not mate with the flange of the '41 transmission.

Question: Is the output shaft of the transmissions the same? Will the flange from the '37 3 speed slip onto the splines of the '41 shaft?

Unfortunately, we do not have access to the '37 3 speed flange today. Hence the question. If they won't fit we have to begin looking at other options.

Thanks for your time,

Justin

The 1941 4 speed is a crude transmissiom with no speeds being syncronized so double clutching is necessary for each change of gears. Also the 1st speed is a super low granny gear used for stump pulling. The transission dates back to 1928. \The original 3 speed is a much better choice..

Justin , I have just explored a similar issue , the '41 driveshaft splines are different to the '37 splines so the U joints cannot be mixed and matched.
I did put a 4spd in a '37 about 30 yrs ago , really cannot remember what was done.
Still working on finding a solution.

edit , I seem to remember the 4spd has a ball U joint on the rear if it is from a 3/4 ton and a spider joint if from a 1 1/2 ton ........ or is it the other way around .

WAIT .......... darn , this is really dragging the memory.

On my '40 , the 4spd has been modified at the rear , to hold an oil seal and has a regular spider type driveshaft U joint .

Hope this waffle has been of some help.

The 3 speed and 4 speed have different u joints and bushes in the front of the rear tube.
I would have to get into the workshop to look and confirm the differences now but I think the 4 speed the bush runs on the driveshaft behing the u joint sleeve where the 3 speed runs on the u joint sleeve. There may be other differences as well.
Tony

Justin,

I have a 1937 1/2 ton and a 1940 1/2 ton pickup truck. The 37 has a 3-speed transmission, and the 40 had a 4-speed until I swapped it out for a 3-speed. If you plan to drive your 37 a lot, especially around town in traffic, you will definitely find the 3-speed to be much more driver-friendly, due to its synchronized 2nd and 3rd gears. Unless you expect to be pulling stumps or driving over curbs or rough terrain, you don't really need that compound low gear used in the 4-speed.

Chevrolet designed the 3 and 4 speed transmissions to be interchangeable on their pickup trucks with a minimum of unique parts required. For the 37-39 pickups, I believe you'll find the transmission output shaft splines to be different between the 3 and 4 speeds, so you'll need the correct U-joint assembly for the transmission you intend to install. If you search for Ebay Item No. 152266013551, you'll see the correct U-joint for a 37-39 1/2 ton (it also fits the 37-39 passenger). Note that the assembly has the speedometer driven gear installed on the forward U-joint yoke. These 37-39 U-joints come up frequently on Ebay, although, often, they don't include the speedometer driven gear. Note also that the 4-speed U-joint is a different animal.

The 3-speed U-joint rear yoke should fit the splines on your propeller shaft and slide right into your torque tube bushing, regardless of which transmission was originally in your truck (assuming you have the stock 37 1/2 ton rear end).

One of the unique parts associated with a swap of a 3-speed for a 4-speed is the master cylinder/clutch-brake pedal pivot bracket. On both transmissions, this bracket bolts to the bell housing and to the side of the transmission case. Because the 3-speed is narrower than the 4-speed,if you're installing a 3-speed in place of a 4-speed, all you need to do is make two spacer bushings 1/2" thick to install between the 4-speed master cylinder bracket mounting lugs and the transmission case. If you're replacing a 3-speed with a 4-speed, you just need to saw off 1/2" from the 3-speed mounting lugs on the 3-speed master cylinder bracket.

The other unique part required for a transmission swap is the floor pan. This is because the shift towers on the 3 and 4-speed transmissions are different. I replaced my steel floor pans with 3/4" plywood floors, cut to size, which I prefer because they better insulate against drive-line noise and engine heat.

While the 37-39 commercial 3-speed transmissions are identical, the front bearing retainer on the 37 is different from the 38 and 39. The 38/39 front bearing retainers have a snout that carries the clutch throw-out bearing, while the 37 does not. These front bearing retainers (at least the 37) are plentiful and show up frequently on Ebay and are interchangeable between all three years. I don't know for sure, but I think the 4-speed front bearing retainer is also interchangeable with the 3-speed.

I have a 37 3-speed truck transmission, complete with U-joint which I intend to sell. However, I have a tentative local buyer. If he doesn't commit in the next two weeks, The transmission will be available for $200, plus shipping.