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Posted By: Spotbiltxo ‘55 engine and tranny. Will it swap? - Tue Sep 14 2021 04:08 AM
I’ve located a 1955 (2nd series) 235 motor, 3-speed tranny, driveshaft, and rear axle for sale. All came out of a half ton truck. I’m really interested in the motor, but since all the other parts are available and match, I am considering buying all of it. I have two questions though…..

1. Is the ‘55 3-speed the same as the one I have in my 1950? (Sm318)

2. Aside from having to relocate the spring perches, will swapping out the old closed torque tube driveline for the ‘55 open rear end involve fabrication or will it be a fairly simple swap?

Thanks
Posted By: tclederman Re: ‘55 engine and tranny. Will it swap? - Tue Sep 14 2021 11:17 AM
Does your 1955-2nd 3-speed transmission attached to an open drive shaft?

Does your 1953 3-speed transmission attach to an enclosed drive shaft?
Posted By: Spotbiltxo Re: ‘55 engine and tranny. Will it swap? - Tue Sep 14 2021 12:12 PM
Tim, I get your point….. answer the two questions and you know if they are the same transmissions. Yes, one currently is attached to an enclosed driveshaft and the other to an open driveshaft, but I’m not familiar enough with transmissions to know if they can both fit either type of driveshaft, or if they can easily be adapted to do so. Can the ‘55 tranny be adapted to fit my current torque tube driveshaft?
Posted By: tclederman Re: ‘55 engine and tranny. Will it swap? - Tue Sep 14 2021 01:32 PM
OK, Chuck

Let's see what others posts.

I think that it/they cannot be easily adapted - either way (earlier to later or later to earlier).
If they can, we will both learn something.
Posted By: Jon G Re: ‘55 engine and tranny. Will it swap? - Tue Sep 14 2021 01:43 PM
Converting the differential from closed driveshaft to open driveshaft involves some work. 1. you have to make spring perches. Honestly speaking the best ones if you have limited experience doing this are what are called clamp-on leaf spring mount pads. These allow you to adjust your pinion angle easily, clamp them down and then weld them in place. Sand off the paint first, naturally. 2. you have to set your pinion angle. It is best to already have your driveshaft when you do this, however you can do this with no driveshaft. There have been scads of articles written about this. Mainly you want the angle of your transmission and the angle of the pinion shaft of your transmission to be the same (one will be + and one will be -)...but you need to add 1 degree or so to the pinion measurement. This is to compensate for spring wrap-up. Now that I've written this, somebody might come along and tell you something else, but the fact is when you apply torque to your rear end, your leaf springs will allow a twisting motion (which worsens with aging) and the extra negative degree I told you to add means your pinion angle will be correct when this happens. If you don't do this, you'll get noise and your U joint will wear oddly. 3. You have to have a driveshaft made or buy one already made. Since you have MANY fewer junkyards today, having one made is a nice savings of time. In San Antonio, deal with Driveshaft Specialists and see if Craig is still there. I've worked with him and you can feel free to use my name. Remember to ask for military discount if you qualify. 4. You may need to use different U joints on your driveshaft...one for the transmission yoke and a different one for the differential. Craig can help you with this.

As for whether the open-driveshaft transmission can be used with the closed driveshaft, no...they're altogether different.
Posted By: Jon G Re: ‘55 engine and tranny. Will it swap? - Tue Sep 14 2021 02:48 PM
I think the angles on mine were around 2.5~3 degrees on both sides plus 1 additional degree (pointing downward) for wrap-up added to the angle at the differential. In very basic terms it looks like this attachment. But if you talk to a dozen different people about this, you might hear a dozen different opinions. And there will be validity to all of them (some more than others and some people may be focused on different applications...such as racing or very heavy hauling, etc). The U joint is happy to work in a range of 1 to 3 degrees. If you exceed that by very much (which happens in Jeeps and other off-road vehicles which are raised for clearance), the U joint can hyperextend and if that happens you can have failure (which if you've ever seen it is ugly and dangerous). I should have mentioned but overlooked...have everything installed...bed, bed wood, fenders, even the spare tire and a tank of gas. Everything that will be on your truck needs to be there when you adjust the angle. Not that it will make a great difference if you have 7 or 8 leafed springs, but it is the way I was taught to do it. Also set your front end correctly and measure about 10 times carefully from front to rear to be certain your rear end and front axle are in harmony and measure the width of your rear axle to your frame, fenders, bed sides and then take a slow and careful look from different angles to be certain it looks right. Your rear end width may or may not match the original width exactly, so you need to allow for that. Good luck!

Attached picture Pinion Angle MD-1.jpg
Posted By: GMCJammer51 Re: ‘55 engine and tranny. Will it swap? - Tue Sep 14 2021 03:10 PM
I found the weld on spring perches at TSC. They are for a trailer axle, but are the same width as your springs and fit your axle tubes. I drilled a new centering holes to move the new axle back to make up for the off set of the old torque tub rear. New u bolts and set the new rear under the pickup with the pickup weight on it. Use a protractor and set the rear pinion angle the same as the ( I used the bell housing ) transmission out put shaft. After everything is centered and the pinion angle the same tack weld the perches in place and remove the rear end and weld them. Finish assembling the rear end and install it under the pickup. I had a drive shaft made for it, around $100.
Posted By: Spotbiltxo Re: ‘55 engine and tranny. Will it swap? - Wed Sep 15 2021 03:44 AM
Jon G, thanks for your detailed comments! You really have a lot of experience to share,

GMCJammer51, thanks for the tip on the perches and their installation.

From everyone’s input it appears that the transmissions are different and therefore not interchangeable. If I go with the ‘55/‘57 235 then I should probably go ahead and buy the matching rear axle and driveshaft to do the job right.

Thanks!
Posted By: Justhorsenround Re: ‘55 engine and tranny. Will it swap? - Wed Sep 15 2021 12:42 PM
Short answer..... YES to your last question.
Posted By: rfs56trk Re: ‘55 engine and tranny. Will it swap? - Wed Sep 15 2021 02:16 PM
It would be a good swap considering all of the replacement components are better than the ones currently in your truck. The 55 rear end would have better gears, 3.90 vs 4.11 that you currently have, and more modern rear brakes. The drive shaft that is included with the replacement parts should work also.
I would do a compression test on the engine and replace seals and gaskets as needed. It may be a good idea to run it on a stand if possible. Remove the side cover on the transmission and look at the gears. The rear cover can be removed from the differential as well.
What you don't want to do is install all these components and then have to remove them to make repairs. There may also be an issue with the bellhousing, rear mounts, and crossmember that will need to be addressed. They are different from 54 up.
Fred
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