The Stovebolt Site Forums The Shop Area Driveline transmission swap 1939 closed to open swap?

question- can a open drive shaft transmission be converted to enclosed on a 1939 chevy-GMC truck.

If its a half ton, it should be closed already (torque tube).

I beleive what texman wat's to know is if he can convert an open drive trans to work with his cloed drive axle. The only conversion i know of is the one for the Saginaw 3.11:1 first gear 4 speed, which is available from Patrick's. I don't know if that kit will work with a pre-War axle, though. There will be an issue with bolt pattern on the bellhousing, too, as that changed in '48.

1939 used a transmission 3 speed that was all by itself. A 4 speed from 1932 to 1947 will fit the clutch housing. 1948 and later used a different bolt pattern on the clutch housing.

Texman, ANYTHING can be done if you put some inginuity and time into it. If I were contemplating this swap, I would look into adapting the back of the early trans casting to the later trans and shortening and resplining the tailshaft.

I am no fan of VCCA but decades ago when they were still focused on technical issues, their magazine G & D had an article on how to adapt 50's era 3-speed gears into '37 and up 3-speed trans cases. That would be way easier than making an open drive trans case work with a torque tube. As I recall it was a simple gear swap except for shortening the later tailshaft, resplining the cut end to match the U-joint and drilling and tapping the back of the tailshaft for the bolt that retains the U-joint.

In the 50's and 60's street rodders adapted Cad-LaSalle open drive transmissions to Ford torque tube driveshafts all the time. I did the same thing with a '37 Buick Roadmaster trans but that was even easier because it was already set up from the factory for closed drive. The Ford U-joint even fit the Buick tailshaft splines!!

Anything can be done. You can do it!

Texman, here's a picture of a '37 Cad/LaSalle transmission on ebay.

http://shop.ebay.com/?_from=R40&...ansmission&_sacat=See-All-Categories

Street rodders used to remove the tailhousing you see in the picture and bolt a Ford torque tube type rear mount/bearing retainer directly to the back of the transmission case. The Ford u-joint would then be mated to the shortened and resplined Cad/LaSalle tailshaft.

It's a very simple machine shop procedure to respline a shortened shaft.

That is the same concept your project would use.

Let me give a more detailed explanation on my question. I have an open driveshaft transmission on my 1939 ton and a half GMC Is it possible to swap out the rear of the open transmission with the enclosed transmission and install in my 1942 Chevy 1/2 ton Both transmissions are 4 speeds

GM used the same 4 speed from 39 to 47. I would think that putting the closed drive shaft on one that was born open should be possible. You will probably have to lay the two side by side and see which parts need to be swapped.