The Stovebolt Site Forums The Shop Area General Truck Talk Gear and tranny change

Hi,

I needs some help with this. I did a search, but didn't come up with what I was looking for. I want to change my tranny and rear end in my 41 3/4 ton. The nonsynchro and super low gearing is a bit of a pain. Engine is a stock rebuilt 216.

Thanks,

Jeff

Help us out a little more. What do you want to accomplish with this change? Do you plan to stay with the original motor?

You're dealing with stuff that is earlier than where I feel confident I can offer solutions. What I can tell you is that the bellhousing on a '41 1/2-ton, and I presume also a '41 3/4-ton, is different that the '48 and later stuff.

The transmission bolt pattern is different, and the bellhousing has a support that has something to do with the clutch pedal. But if you are changing motors too, that kind of information can become irrelevant.

What are you trying to accomplish?

I'm keeping the 216 engine because it was just rebuilt. I really want a transmission with synchro that's more modern, like a T-5. The transmission is the big thing. Because the truck is only going to be driven on short runs and around town, I don't mind the 4.57 gearing. I'm trying to keep the truck as original as possible, but I need a better transmission.

Jeff

Several of us have put a T-5 trans into an Art Deco truck. The heart of the conversion is a transmission adapter plate. You won't be sorry if you do it. Look it up on the Tech Tips icon at the top of this page.

The 3 speeds they used for the art decos are at least partially syncroed. You would not be able to downshift from 2 to 1.

Is your 3/4 ton an open drive train, or torque tube setup. If it is open you would have more choices like a t-5, without having to change your rear end too. Look up Steppinwood and cavebull's art deco transmission swap pictures. You will get a good idea for what is involved for a t-5 swap.

I'm not sure, but I think mine's a torque tube. Can the T-5 swap still be done if it is?

Jeff

If your truck has a torque tube its going to be more work than it may be worth to adapt something like a T-5. I'm sure it could be done, but it might require a smart fabricator and machinist.

Patrick's used to offer a kit that put a Saginaw 4-speed in a torque tube AD. While its not OD, it is fully synchomesh and more pleasant to drive. I have no idea if that kit would work on a '41 3/4-ton.

OK, then a different differential is needed to do the T-5 job right. What would be a good choice? I would like to have 3.90 gear ratio minimum.

Jeff

Isn't your truck open drive line past the carrier bearing? Advance Design 3/4 tons have open rears, but are closed drive line from the trans to the carrier bearing. I think Art Decos are the same configuration, but I am not positive.

I'm really new at this. Please explain what an open driveline is. My driveline is a 2 piece type.

Jeff

An open drive shaft has the part that turns exposed. A closed drive shaft has a stationary tube over it. Yours is closed on the front part & open in the rear section. That will make it ok to put in a different trans without changing the rear end. A drive shaft shop can make up a drive shaft to fit the conversion.

Jeff,i am posting a picture of an 1951 torque tube rearend "enclosed driveline".This is a one piece driveline for a 3100 series truck.Instead of an open driveshaft,the tube has a propellor shaft inside it and connects to the transmission with a u-joint.This rear end is for an AD truck . I hope this helps.

1951 torque tube rearend

This should explain what you have now. (Disassembly and reassembly of the two piece driveshaft from the 1941 Shop Manual)

http://chevy.tocmp.com/1941shop/41csm109.htm


Open driveline uses u joints at both ends of the driveshaft and is not enclosed.

http://en.wikipedia.org/wiki/Hotchkiss_drive

Torque tube definition.

http://en.wikipedia.org/wiki/Torque_tube

More driveline definitions.

http://www.bchra.org/TipsTricks/RearAxleBasics.htm

Hope this helps.

I have a 41 3/4 ton. I just pulled a T-5 at a U-Pull-It last week. Behind the transmission is a short torque tube with the end mounted in a carrier bearing. From the carrier bearing to the rear-end is an open driveshaft. I'm planning on installing the T-5 and having a driveshaft made up to replace the short torque tube and leave the open driveshaft in place (assuming I can get the u-joint between shafts matched up)

Baldbaron;
Read this, from a thread entitled," "51 3800 216 gear ratios" in "Big Bolts". I had the same problem.

And... here it is. Picked her up a couple hours ago, and I've driven 20 or 30 miles in a bunch of different conditions. To review, what I've done is change the differential gear ratio from a far-too-short 5.14 to 4.10. Nothing else substantial except for whatever bearings were exposed in the process (all of 'em), and the front wheel bearings to boot.
Here are my early impressions: First gear is now useable for something other than rock climbing. I stopped on a 15% grade. 1st gear was (of course) an easy start almost without any throttle. At about 10mph I shifted to 2nd smoothly and easily without having raced the engine, and 2nd pulled away nicely. Ditto 3rd, and I levelled off at around 30 mph in the middle of third at a moderate throttle setting. Keep in mind that at 15%, the grade I ran was almost 3 times as steep as the steepest interstate. I could easily have gone fast enough to pick up 4th, but I'd have been exceeding the speed limit. Probably couldn't have held fourth anyway. So at the top I shifted up and idled very nicely at around 35mph at the very bottom of 4th.
Then I took to a freeway. Evelyn followed me with her certified speedometer. It's German, you know. Therefore, of course, superior. Right. First I tried for my fastest comfortably sustainable cruise: 58 or 59 mph, she said. I could do that all day. But I also tried a "fuel miser" cruise, which turned out to be exactly 50mph. At that speed I could actually downshift, dump the throttle and scream up to 55 just like that! I didn't do that - no reason to - but I could have. I have the distinct feeling that the next time Epic is asked to haul a load that would void a new truck's warranty, she'll do it without a hitch, exactly like this, but at a slightly higher rate of fuel consumption.

There is no problem here, I'm telling you.
This is exactly what I was looking for. A truck that will still lift your house, but can now eat great distances without straining. I think I'll stay with this for a while. 2nd is still a flat ground starting gear. I don't need an overdrive, and probably wouldn't unless I really started to sock on the featherweight highway miles. Even then, this would do nicely, I think.

-Mark

p.s., My transmission is a SM420, synchro in 2-3-4.