The Stovebolt Site Forums The Shop Area Driveline 1950 - Torque Tube / Rearend help

Looking for help on my 50. I want to retain the 6 lug wheels but want to upgrade to a late model rear for a few reasons. The truck sits on its original frame now and has the stock rear, torque tube and manual trans. Is there a way to use the stock manual trans and late model rearend with a later model driveshaft? Appreciate any comments and help

1950 Chevrolet 1/2 ton?

You cannot easily use any part of the torque-tube drive-train with a 1955 or later model rear end.

What are the reasons for the upgrade?
Better cruising RPMs?
What size 16" tires do you now have?

You can use your existing drivetrain with the following "upgrades"/adaptations/changes to obtain lower RPMs at higher speeds.

- change from 4.11 ring&pinion to 3.55 ring and pinion
(16% lower RPMs when cruising)
- change to 16" truck radial tires (31.5" rolling diameter vs your < 28" rolling diameter)
(another 12% lower RPMs at higher speeds)

Well to fully disclose my situation - I wanted to maintain originality on the outside and as much of the original chassis as i can. When my uncle was working on the truck, he did the brakes - but never added brake fluid. That was 20 years ago so - I need to replace/ rebuild at least the MC and wheel cylinders. I am also missing 2 drums. So with that plus the fact that I would love to make it more highway worthy with a friendly gear set and better brakes.........leads me to the mods. The truck has a manual trans - rebuilt and lubed. I intended to keep the manual trans, which I thought would require the use of the torque tube. I would love to change it to auto trans too but not sure how to maintain the shifter on the column. Changing everything over from trans back to rearend may be best way to go, but I dont want to lose 6 lug or the column shift.........

If the transmission is an SM420, you can very easily convert it to use with an open driveshaft. It only requires that the rear bearing retainer and the yoke be swapped. Those parts come up fairly regularly on everyone's favorite auction site.

I know the trans is original, but how can I ID it as an SM420? Is there an aftermarket swap kit also? Not sure how I would search for those parts or what to call them to get the right ones to make the swap.?

Novak Transmission guide to SM420. If you have an enclosed driveshaft 4-speed on a 1948 or later 3100, it is almost certainly an SM420.

I have never seen a torque-tube to to open-drive-shaft swap kit (as a packaged full kit) - most people try to find a 1955 or later SM420 "open" rear-cover and "open" u-joint assembly. Maybe post a want ad here in the Swap Meet, or check eBay, or find/use a craigslist nationwide search engine? If someone knows about a "packaged" swap kit, maybe they will post manufacture/vendor information?

In your first post, you indicated that you want to "retain the 6 lug wheels". The original 1950 3100 6-lug wheels? What open rear-end are you considering?

He talks about retaining the shifter on the column, so leads me to believe he has the three speed trans and not the sm420.

You are correct, sstock, but he did ask specifically about SM420.

"The truck has a manual trans - rebuilt and lubed. I intended to keep the manual trans, which I thought would require the use of the torque tube. I would love to change it to auto trans too but not sure how to maintain the shifter on the column. "

"I know the trans is original, but how can I ID it as an SM420?"

That link should easily help to differentiate any 3-speed from an SM420 (and, settle that question)?

My trans is a 3 speed manual - shifts on column. original set up.

"I know the trans is original, but how can I ID it as an SM420?"

An SM420 is a four speed.
What are you hoping to ID?

Well the current question is if my original 3spd can be converted to an open driveshaft arrangement.

I say "no", but I am interested in hearing if I am wrong.

I agreed with tclederman and say no also, the 3 speed trans that is used with the torque.
Its rear main output shaft bearing lets tranny lube flow back and forth from the tranny to the u-joint ball housing and back.
Unless there is away to seal the rear main output shaft bearing from letting tranny lube pass it.
You might be able to change out the rear support housing to a open housing. Picture

There is no way that I know of to convert a 3 speed to open driveline. To me, it seems that the best option would be to fund a '55 or newer transmission. No matter what route you go, it will require fabricating a driveshaft.

Just wondering... why do you want to get rid of the torque tube?

Yes, my 54 3600 series had an open driveline 3 speed. I believe the 54 and early 55's had this arrangement. I can't say if the 55-59 trucks were the same. On the pre-54 3600 trucks, they had partial torque tube transmissions, you would need to install a carrier bearing assembly and crossmember to make it work. On another note, I had a 3 speed from a 235 powered El Camino, the shift levers were different than what was on my truck. It may may have been possible to modify the El Camino shift levers, can't really say.

When you are road ready, what is your goal for this truck?

Around town in style?
Highway cruiser?
Cross country road trip?

This question needs answered in order to point you in the best direction. Also please provide what engine is pushing all this. If your existing driveline is in decent shape, I would strongly recommend just getting the truck drivable and just drive it. The reason for this is to really make up your mind about the truck’s setup. Many change their minds once they get some seat time. I know I fell into that category.

Better to change your mind before you really start then after spending a lot of time changing things from the start.

"Well the current question is if my original 3spd can be converted to an open driveshaft arrangement."

The poster asking if his 3-speed closed drive shaft transmission (the transmission itself) can be converted to an open driveshaft (similar to how an SM420 transmission itself can be converted)?

That transmission cannot be converted.

Is there a short enclosed-u-joint housing/extension on some Chevrolet 3/4 tons or GMC longbed 1/2 tons that are then connected to an open driveshaft?

Tim said "Is there a short enclosed-u-joint housing/extension on some Chevrolet 3/4 tons or GMC longbed 1/2 tons that are then connected to an open driveshaft?"

Yes, my 51 3600 with it's SM420 had a enclosed driveshaft to the carrier bearing. From the carrier bearing to the rearend it was a typical open driveshaft.

Now, I'm totally out of my area of 1st hand knowledge but could one not duplicate the 3600 style enclosed/open driveshaft with the three speed which is what I believe tclederman was saying? A bit of measuring, cutting, fabbing/welding up the driveshafts and cross member for the new carrier bearing and one's in business, a nice weekend project.

Good luck, RonR

All of the driveshaft fabricating seems like a lot of work if the original torque tube driveline is operable. My question of the moment is why not just retain the torque tube?

Without re-reading, I believe the op wants to keep his 3-on-the-tree and change the rearend for an upgrade to higher gears.

Yes, RonR, that is what I was referring to - thanks.

Yes, 8trackdude, I agree with your post.

This shows the u-joint arrangement for 54 trucks. The top pic is 3100 with torque tube, the bottom is 3600 and larger.
http://chevy.oldcarmanualproject.com/chevyresto/54137.htm

Here's the 53 and earlier. It shows the torque tube setup for the 3100. The 3600 & 3700 just have a front torque tube. Then the 3800 and larger are open drive lines.
http://chevy.oldcarmanualproject.com/chevyresto/53137.htm

The 3 speed and 4 speed, SM 420, were options for the the 3100 and 3600 trucks. The SM 420 was only offered in the 3800 and larger trucks. So, finding a 3600 with 3 speed is whats needed, along with an open driveshaft rearend, which there are many options out there.

Correct. but also want improved brakes in rear too. Do they offer disc brakes for the original diff. on these trucks? I havent run accross them.

I have never heard of rear disc brake conversions ever being offered for an original differential for that year. What I do know, is that a 2000 Chevy S10 4 wheel drive was available with rear disc brakes "and they were 6 lug wheels". Although, I am not sure how compatible that would be with the rest of the truck (spring mounts, track width etc). Maybe a possibility though.

Correction: 2000 S10 did not have 6 lug wheels. Sorry for the incorrect information.

John

No discs that I am aware of, but you can swap the original huck brakes for the '51 and newer Bendix units (standard modern drum brakes). You would need everything from the drums to the backing plates, but add far as i know, it is a bolt-on upgrade.