1955 1st series 4 speed tranny

[akeane01]

hi,

I have a 1955 1st series C3100 truck with a 3 speed. I would like to convert that to a 4 speed on the floor instead. Does anyone know what transmissions will fit the truck? I think there was a 4speed option on the original truck..

thanks

[raycow]

Any 1955-67 SM420 transmission will bolt to your stock bellhousing and fit your existing clutch. Some of these from larger trucks had a parking brake mounted on the rear. You don't need this, but it won't cause any major problems as long as you remove the unneeded parts. Avoid the 54-earlier transmissions intended for a torque tube as these will need modification to work with open drive.

Whichever transmission you get, you will need to replace the driveshaft, and of course cut a hole for the shifter.

Ray

[akeane01]

ok, thanks

I was asking since I saw that blue 55 truck someone found recently in the barn with the 4speed so it perked my interest..

Let me ask this.. Was a 4 speed an option on the 55 1st series C3100 truck?

alan

[raycow]

Originally Posted by akeane01

Was a 4 speed an option on the 55 1st series C3100 truck?

Yes, it was an option on almost any truck that came with a 3 speed as base equipment.

Ray

[akeane01]

ray,

I have been reading posts and yours as well in other areas.

Can you straighten me out on the 4 speed transmission. I think i would like that better than the 3speed onthe column but not sure.

I see that the SM420 works from 55-67 and will bolt up ok. I read that the transmission is noisy and had low gearing. You put in a T5 with a spacer that was needed if I got that all correct.

I am not sure where to get the driveshafts but it seems like it will need to be modified.

I am unsure on direction at this point and ask what you think is the best option for my 55 C3100?

alan

[raycow]

Originally Posted by akeane01

I am unsure on direction at this point and ask what you think is the best option for my 55 C3100?

It all depends on your intended use of the truck.

If you plan to use your truck for towing or other hard pulling, the 4 speed is a worthwhile upgrade because of its extra low 1st gear. Otherwise, you don't really gain much for general driving. When I had my 4 speed I never used 1st gear, so it was effectively a 3 speed.

If you want more comfortable highway driving, consider some kind of overdrive transmission. The T5 is one possibility, but you could also use a 3 speed with overdrive, which was a factory option and would allow a slightly easier installation.

If all you want is to get rid of the column shift, you could install a floor shift conversion on your present 3 speed, assuming you don't have any other problems with it.

My truck originally had a SM420 and a 3.90 rear, which was very unpleasant at highway speed. Any useful rear axle swap would have involved welding on the axle housing, which I didn't particularly want to do. Instead, I went with the T5 because it has an overdrive 5th gear. However, if my truck had come with a 3 speed instead of a 4 speed, I would have replaced it with a 3 speed + overdrive. Btw, I did not use a spacer with the T5, but shortened its input shaft and bearing retainer instead.

For most transmission swaps you will likely need to modify or replace your driveshaft. I got lucky and found a salvage yard driveshaft that was the right length, so all I had to do was swap the yoke. If you can't find the exact length you need, just get one that is too long and have a driveshaft shop shorten it.

Ray