The Stovebolt Site Forums The Shop Area Driveline 3 to 4 speed tranny conversion 49 Chevy 1/2 ton

I've recently ran into a problem with a tranny swap. I pulled out the original 3 speed column tranny and tried putting a 4 speed toploader from a 50 3/4 ton in but the splines are a different size on the shaft in the torque tube from the 1/2 ton than those on the coupler on the tranny. Is there a conversion for adapting the two together or am I beating a dead horse. If so what would be my best option for puting a floor shifter in my 49 1/2 Ton.

Thanks
Jason

Is it the splines of the ball joint that is different than that of the splines on the end of the shaft of the torque tube? If so, can't you replace the ball joint with one that matches?

The ball joint on the 4 speed is bigger than that of the 3 speed and won't fit the coupling of the 3 speed.

I'd make a call to Steve at Buffalo Ent. this man knows every Chevy trick in the book and may be able to solve this.
Ph. 360 652-7684

So how about using a 4speed ball joint from a 1/2t application? Will it fit the back end of the tranny? What is the tranny model number?

ball joint? or u-joint?

Maybe use the 4-speed front yoke (from an enclosed driveshaft SM420) and the 3-speed rear yoke? My memory is bad and I cannot remember if that is the correct configuration. Wait to hear from someone else.

Yes a U joint. So is the drive shaft from a 3 speed setup different than a rig that had a 4 speed? Or is the problem adapting a 3/4t tranny in a 1/2t truck?

The drive-shafts might be different and there might be a problem adapting a 3/4 ton transmission to a 1/2 ton truck.

Depends on the years.
- None, one or the other, or both might have had enclosed driveshaft fitting at the rear of the transmission.
- One or the other driveshaft might have been a closed driveshaft, or have an open driveshaft or have a short enclosed extension "shaft" behind the transmission.

The most useful way to get an answer/suggestion/opinion is to identify (in words or photos) the transmission types, the fitting at the rear of the transmission and the type of drive shaft end that goes/went into the transmission (as I think that Jason has done).

If Jason is referring to:
- an original 3-speed transmission from a 1950 1/2 ton Chevrolet truck, that would have been an enclosed driveshaft.
- an original 4-speed transmission from a 1950 3/4 ton Chevrolet truck, that would have been an SM420 4-speed transmission that was set up for an enclosed driveshaft.

In this case, the appropriate u-joint assembly would be: a front yoke for an enclosed SM420 4-speed and a rear yoke for an enclosed driveshaft 1/2 ton rear-end.
In this case, maybe someone will post information on yokes, joint, and bushings/trunnion-bearings (if needed - I forget what they look like) that would work in this application.

Or, post a want-ad in the Swap Meet (I got a set from Bruce Bugay and from WD Foster); or, call Jim Carter (he might have a used or rebuilt assembly).

I actually have a u-joint assembly off of a I think 3/4 truck I will not need. Let me get back to you with some details.

Walt Williams
La Verkin, UT

In my 1953 chev. 3100 1/2 ton the U joint failed and I am looking for the yoke that fits on trans. side of the U joint. Any suggestions?

Post a Want Ad in the Swap Meet.

Found yoke after searching the entire U.S., was about to take my old one to the machine shop, weld in the damaged areas and re-tap. had two salvage yards call one was twice as much as the other. Im just bout ready to be back on the road.