The Stovebolt Site Forums The Shop Area Driveline How to hook a non torque tube tranny to a torque tube axle?

I recently bought a 54 chevy 3100 that was complete except the engine and tranny. I bought the engine and 4 speed from a 57 chevy truck. The 54 has a torque tube axle and the 57 had the open drive shaft. I was told I can adapt the tranny to the axle by removing the yolk and fitting a different piece but so far I have not been able to figure it out. My axle has ball shaped piece that I assume holds oil on the u joint. I assume I need the u joint that uses oil and the other end of the oil seal that bolts to the tranny. Has anyone ever adapted this tranny to a torque tube? Can anyone tell me the name of the parts I need? Anyone have any pictures?

Thanks

Jonald,

The only open drive-shaft transmission that can be "adapted" to work with a torque-tube rear end is the SM420 4-speed that was made from 1955 through around 1962. From 1948 through 1954, the SM420 was set up for the torque-tube.

It is possible to swap the SM420 rear housing/cover and complete u-joint assembly (including both yokes) from a closed driveshaft SM420 transmission onto an open driveshaft SM420.

Do you have a 1957 4-speed truck transmission? It is most likely an SM420. You would need to find the rear cover and complete u-joint assembly/housing from a 1948-1954 SM420.

Thanks for the reply. Yes both engine and tranny came out of a 57 4 speed truck. Anyone know a source to buy the u joint assembly and rear cover?

The more I think about this the more I think I would like to get rid of the enclosed drive and go to the open drive shaft. Would it be possible to keep the stock axle housing and trade out the pumpkin and torque tube for just a diff with a yoke? I would think the torque tube would keep the axle from twisting under heavy load or quick acceleration. Would some type of link bar need to be added if I went to the open drive shaft?

Thanks again

No
No

If you get a non-torque tube rear axle with better ratios, brakes,etc., you will need to allow for not allowing the new rear axle to rotate, which the torque tube did-proper spring hangars.

Ed

tclederman, why couldn't he "keep the stock axle housing and trade out the pumpkin and torque tube for just a diff with a yoke" from a '55-'62 1/2 ton as I and many others have done?

Jonald, unless I'm missing something, you should be able to swap your center section for a non torque tube unit. Also, you are correct about the torque tube stabilizing the rear end. You'll need to weld up the spring mount pivots on the axle to prevent axle roll.

"Would it be possible to keep the stock axle housing [the torque-tube axle housing] and trade out the pumpkin and torque tube for just a diff with a yoke?"

Jonald,

I might not understand the original question.

It looks like he would like to place the guts of a later non-torque-tube differential inside the torque-tube rear-end (minus the torque-tube).
This is outside my understanding/experience, but, how would you seal the forward part of the torque-tube housing?

Maybe there is a front cover for an open drive-shaft that will bolt onto the torque housing?

Is this the information that you need? open drive

The rear axle in my '53 GMC 1/2 ton is a stock housing, brakes, axles, etc. I replaced the original torque tube differential with a '55 - '62 3. 90 differential .

You'll want to start by setting your pinion angle and welding the spring perch pivots solid. Then it's as simple as removing the rear cover, disconnecting the axles and moving them out a bit, unbolting and removing the torque tube differential, sliding the new differential into the housing (with a new gasket of course) and bolting it in place, sliding the axles back into place and connecting them, replacing the rear cover, and filling with gear lube.

Now of course you have to find a driveshaft or you're not going anywhere.

Thanks to everyone who responded (with experience).

Why is this not done more often?

Is it hard to find a 55-62 higher-speed R&P?
The original poster has/had a 1954 3.90 enclosed driveshaft R&P.
Obviously, a readily available 3.90 would be better than a 48-53 4.11.

And, this would be faster, easier, and maybe less expensive than a 3.55 R&P conversion (around $300, plus all installation parts/bearings, which might/would be needed either way).

The 3.90 was standard in '55-'62 so it's a relatively easy ratio to find. I got one for free and paid $75.00 for the other which is plenty cheap. The only other needed expense is a couple gaskets and new lube. Of course, if you're going to do it, it's a good idea to replace the bearings, but that's a small expense.

Next comes the drive shaft. You'll have to have one made or a used one shortened. I'm running a T5 with an adapter plate from Hamilton Intakes. I was able to use a stock/unmodified drive shaft from a mid '90s Astro van with the yoke from an S10 drive shaft which made it the perfect length.

Also, the .72 overdrive with the 3.90 rear end and 255/70/15 tires allows me to run 75 mph with my old 216 and the speedometer is spot on.

The entire swap (transmission, drive shaft, rear end) is so simple I was able to do it with simple hand tools (except for welding the spring perches) in the front yard in half a day.