The Stovebolt Site Forums The Shop Area Driveline 49 driveline swap

Hi all ,I am going to swap rear end on my 1949 3100 suburban and wondered if anyone has information on the diameter and number of splines on the output shaft of the gearbox . I don't want to take the axle and torque tube off without knowing this as I am in the UK and need to find the parts first ( not so easy here) The trans is a 4 speed with granny low thank you Jon

Hy jon mattey, your truck should have an SM420 transmission in it, they started in 1948, so that is what you need to buy parts for. You could swap just the center section of the rear axle if you could find the center section from a 55B through 62 1/2ton, hope that helps.

Does your transmission have after it an enclosed driveshaft (I think so)?
If you want to use a rear axle or center section as 3B suggest with open driveshaft you need transmission with open driveshaft.

If enclosed now you can swap some parts around on the back of your transmission from another SM420 with with open drive line to allow use of an open driveshaft. Or swap entire transmission.

I have done the same swap on my 49_ 3100truck. Just get the open drive part that goes on the transmission. You remove the center section from the rear end, replace it with the "new" center section back in with the "c" keepers. You should get a new crush sleeve also. You'll have to measure and get a new drive shaft built. Here's the hard part. You will have to weld the spring perches or cut them out and replace them with a set of new ones that are available through Classic Part or Jim Carter's just to name a couple. This keeps the tires in the center of the wheel well. I tried welding my first swap and it lasted a while and it broke. Thank goodness it broke in my driveway. It will brake. Just a question of when. So I advise the perches. Little more work but well worth it. The reason the weld doesn't hold (generaly) is because there is rubber inside the old perches and you really can't get a good weld on it that will hold. You will have to order some more u-bolts but they are not that expensive. Mine now works great. Another good point, I have a 390 ratio in mine. When and if I find a better ratio it is just a matter of removing the center section and replacing it with the new one. All the hard work is already done. Hope this helps. Sorry it is so long but trying to let you know what it takes. If I've missed something I'm sure someone will take up the slack. Good luck.