The Stovebolt Site Forums The Shop Area Driveline Questions about my transmission

Attached is a photo of the transmission in my '49 Chevy 3100 1/2 ton I am restoring. It has 4 shifter slots so it is a 3 speed. I cannot find many references to this transmission in the forums or elsewhere.
1). What is a description of this transmission that I can use for parts ordering etc?

2). Other than checking the fluid level, do I need to do anything to this if it appears alright? It shifts fine. How about the universal joint at the top of the torque tube? Should I check anything there before putting it back into service?

3). When putting the engine back with the transmission still in the vehicle, is it straight forward or is there a "trick" to it?

Best regards and thanks,

Joe

Sure looks like an SM-420 4-speed to my untrained eye. To be certain, check the part number on the drivers side (591665). Attached are some pictures of the SM-420 from my '49 3100 you can compare.

Regarding your questions:
1. SM-420 I'm pretty sure
2. Depends on your plans for the truck. On one hand, if it works, you could say don't mess with it. But I can tell you when I took mine open it was full of sludge. Likely never having been open before, and who knows what different oils were in it over the years. It also leaked like a sieve, which I wanted to at least slow down. Here are some pictures I took while working on mine - SM-420 Transmission In a more direct answer to your question, besides just checking the oil level, it might be a good idea to slide the universal ball cover back and check to be sure the universal joint bolts are tight.
3. I would strongly recommend you get (or make) guide pins. I tried for a while to get my transmission lined up without them, but finally gave up. To make them, just get longer 3/4" bolts, about 3-4" I think, cut the heads off and screw them into a couple of the mounting holes. This will help you get everything lined up.

Greg's reply is very helpful.

The use of two mounting-studs (called "guide pins" in the Shop Manual) makes removal/replacement much safer/easier.

Here is information about the SM420 transmission.
ID/casting codes are listed.

The rear housing for the torque-tube u-joint can be swapped on/off any year SM420.

u-joint parts are available from several vendors

The Shop Manual describes removal/installation:
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0713.htm

As what I believe Greg has done, I would install the motor first. With the SM420 not in place, it gives you lots of more wiggle room. Once the motor is roughed in, I would then install the SM420 by sliding it under the truck and then raise it with a engine hoist and slide it into place.

Oh and during removal, I remove the SM420 first again with an engine hoist. Disconnect and lower it to the ground (reverse of the above install method).

The 3 speed would have shifted from the column with external bracketry. Your transmission is a 4 speed with granny low as the others have stated. 🛠