55 Century differential to 47 Roadmaster?

[Guest sherlok]

Hi,

I know it's not prewar, but would the differential cluster (or pumpkin) of a 1955 Century fit the 1947 Roadmaster? Trying to raise the gearing a bit.

How big of a job is it?

Thank you,

Sherlok

[The Old Guy]

Do a search. There are numerous threads on this subject, but in a word, YES. The centers will interchange from 1940 to 1955. The big problem is getting the drive shaft switched, unless you are lucky enough to have them both the same length.

[Guest sherlok]

Thank you,

I did do a search shortly after making the post and found the information. But, I'm not sure what you mean about the drive shaft length. Why would that change?

Regards,

Sherlok

[Fred Rawling]

If the drive shaft length is different you will have to remove the pinion from your drive shaft and the pinion from the parts drive shaft. That can be a real chore but installing the new dirve shaft and adjusting it to the run out specified in the shop manuel can be even harder.

[The Old Guy]

The drive shaft and torque tube are attacned to the center section. The tube unbolts, but the drive shaft is attached to the pinion gear with a splined collar. This collar is pinned to the pinion. The problem is that different cars have different wheelbases and different length transmissions. The drive shaft and torque tube are different lengthes to compensate for this. If you were to install one that was a different length, your rear axle would not be centered in the fender opening ,and would cause serious problems.

[Guest sherlok]

Well Old Guy and Fred, I thought this might not be a piece of cake, but I did not realize it would be that difficult. Living with the 4.11 rear end sounds like a real good idea.

Thank you for your help,

Sherlok

[The Old Guy]

If you are planning on driving your 47 any distance at all, it is well worth the effort. I have put over 104,000 on my 40 ,and it made it so I can run the interstates and not feel that I am slowing people down.

[Fred Rawling]

Well Sherlock, if you are going to drive it, bite the bullet and make the change.

There is a guy advertising a puller for the pinion in the Buick Bugle.

Pulling the rear end from the car is easy. With the tool you should be able to pull the pinion off your drive shaft and installing the new one is easy. Getting the pinion off my drive line was the most difficult and time consuming but I did not have a puller. I had to figure out how to do it from scratch. You have to be careful not to bend the drive shaft when you are pulling the pinion.

Swaping the ring gear from one pumpkin to the other was easy and I used some modern motor cycle gear case sealer on the seal between the torque tube and pumpkin.

You need a machinist or a rear end shop who is willing to fool around lining up the drive shaft in the pumpkin so that the run out is .015. You should take the pumpkin with the ring gear installed and the drive shaft installed to the shop.

The first 2 shops that I went to had no idea what I was talking about. The third guy did it for $75.00.

The tool to space the pinion bearing is described in the shop manuel. I made one out af a 1/4 inch piece of steel with a welded a handle on it.

[Guest sherlok]

Wow! I used to work on 50's Fords and Chevys in my youth. I guess my buddies and I were lucky. We just bolted the stuff back together and they seemed to run OK.

I think I might wait until I get fully retired before I take on this project. With my schedule, it could put my car out of service for a good while. As it is I use my cars regularly to show property (historic houses) to customers.

I really appreciate your advice.

Yours Truly,

Sherlok

[old-tank]

If you change your mind I have a puller/installer that I made. You can borrow it at any time. It has been used on 4 driveshafts and none needed straightening after installation on the splined pinion.

Willie

[Guest sherlok]

A very nice offer, Old Tank. We have a small home in Athens, Texas where we plan to spend more and more time (grandchildren). It would give us a good excuse to revisit wonderful San Antonio.

I'm working toward retiring in a couple of more years, hopefully sooner. I may take you up on your offer then.

In the meantime, thank you for your help and the others who have responded.

Regards, Sherlok

[FireballV8]

Hi Willie

We are doind this right now, but from a 55 to a 48 Roadmaster. In your picture does it show the tool in position for reinstallation of the drive shaft?

Also how do you do the measurement for the spacing as Fred described?

thx

Steve

[old-tank]

Hey Steve

It is positioned for installation in the picture. You and others are welcome to borrow also. Here are links to other pictures:

web page

web page2

web page3

I made it from front and rear flanges of an old torque tube...the front flange is halved to fit the groove in the rear of the drive shaft.

Willie