The Stovebolt Site Forums The Shop Area Engine Shop SM420 to open drive line

Ok, I searched and could not find, so...

I have a SM420 from a 52 long bed with a torque-tube drive line. I need to couple it to an open drive-shaft which will connect to a mid '70s 3/4 ton rear-end. I've seen pictures of an SM420 online with this desired setup. Can anyone share any knowledge of an aftermarket or later model rear transmission cover plate that will couple to an open drive-shaft u-joint yoke?

Thanks. This website rocks!

Any chevrolet or gmc truck with an sm420 newer then 1955 should have the proper rear cover and yoke that you want. They used this tranny through 1967 and even into the 1980s on some larger trucks and military trucks.

Jeff

Sorry, I forgot to mention that this truck had a 58-60 something 235 in it, and I assumed that the transmission was also non-original since I've never seen this 4 on the floor setup with any other 52 GMC's.

So later model 420's came with an open drive-line setup? Maybe this thing is original then.

Thanks.

Is your truck a 1/2 ton long bed or a 3/4 ton?
You mention you are putting in a later 3/4 ton rear...
If your truck is a 3/4 ton you already have an open drive shaft from the carrier bearing on back.

Steve, it's a 100 series, longbed, '52 GMC. (1/2 ton)

So the 3/4 tons came with open drive-shafts before 1955?

Wondering why you want to put a 3/4 ton rear in it?
3600's had a 2 pc. drive shaft with the front being torque tube and the rear open.

The 3/4 ton rear-end I have has a nice gear ratio. 3.11 or 3.07 to 1 (I forgot which).

Larger trucks with an SM420 had open drive also. There should be a lot of open drive type SM420's out there, and you can either swap the entire transmission or just the pieces at the back.

Another reason I used that rear end is so I can use my original wheels (it's a six lug).

Well, thanks guys. I'll get on ebay and see what I can find.

Dave

6 lug 3/4 ton?? Would have to be an '88-'94 14 bolt semi floater, anything before that would be 8 lug.

I've got an open driveline SM420 in my garage that I'm not using, PM me if you want to buy it.

That rear is going to be a little wide for your truck.
I think the 6 lug 3/4 tons went a little later than '94.
I just retired a '96 3/4 ton shop truck that was a 6 lug.
Over 325,000 miles on the same engine, no rebuilds!

Just an update in case anyone searches this topic:

The rear end was a 1/2-ton six-lug 3.07:1.

I went to Novak trans parts and got some rebuild parts along with the open driveshaft rear trans plate cover. Still haven't found a drive shaft. It has to be a 2 peace (with the slip splines between the u-joints) because the yoke at the transmission is fixed. I might have to go to a shop to have one custom built.