The Stovebolt Site Forums The Shop Area Engine Shop Rear end swap torque tube vs open on 48 Chev

Hi, I have an open rear end from a 1955 GMC that I want to replace my torque tube rear end with. I have ate 3 u-joints and two since I replaced the torque tube bushings. I really want an open drive line, tired of messing with the enclosed one. I would like any tips and or help with this swap out. I have a parts SM-420 that has the open driveline out put shaft, and I have the complete 55 GMC rear end. I will be updating the shocks too. What other parts am I missing out on??? Is there a difference in gearing between the 48 Chev stock enclosed and the 55 GMC open????
Thanks again, Garry

Your 48 1/2-ton rear end has a 4.11 (or 4.10) ratio. The 55 is 3.90. Is it from a 55-1st or 2nd series pickup? I am real sure that the 55-1st will be a direct swap into your 48. Spring perches will line up, etc. Same for same, good swap for that truck. The 55-2nd and later (thru 59?) may be just as easy. Do some measuring: spring centers, overall width, etc. to be sure. You'll have to get or make a correct drive shaft. Good luck.

Like Frank50 says , this is a good easy swap for your truck ,
I have a '55 diff in my '40 .
The spring mount is completely different as you will see when you examine them . But easy to build.
Important part is having the diff pinion at the correct angle to the trans output shaft.
After you have the new diff in , you will find the rear brakes will lock up cause they are Bendix , and you have Huck brakes on the front of your '48 . You will need to fit Bendix brakes to the front as well , for safety.
I did this after a nasty scare with the trailer on ,, works well now.
Look in the tech tips section .

edit , here is the link.

http://www.stovebolt.com/techtips/55rear.htm

The quick way? Take the torque tube and center section out of your existing rear axle housing. Put the center section from the 55 in your existing housing. It will bolt right in. Axles will fit too. You should replace all related seals and check the bearings.

Install your open driveshaft tranny, should bolt right in. Get a drive shaft made.

Now the important part. Weld the pivots solid on your existing housing. The torque tube housing pivots at these points because of the lack of u-joints. With an open driveshaft with u-joints, the u-joints provide the pivot and the originals pivots have to be welded solid.

Are you confused yet? I did this to mine and have not had any troubles. If you need me to post pictures of my setup, let me know.

Point is, you do not have to change the housing unless you want to center the wheels in the fender opening. If you want the wheels centered, you will have to make new axle mounts.

Or, if you have access to an ~'82 Firebird/Camaro six cylinder, you can put in the tranny and the 3.73 rear end and use the springs that came with your truck.

[img]http://www.utdallas.edu/~pauls/trucks/images/left_spring_mount.jpg[/img]

afu45 , thats really good info , does the 55 pumpkin fit into the 41 - 46 housing also ?
And did you use the 55 axles or the original axles .? Thanks .

Dusty: Sorry, I can't answer your question about those year models. Maybe someone else can.

I used one of the torque tube axles and one of the 55 axles. One of the torque tube axles was damaged. They are the same between both differentials, but are different lengths from side to side.

THANKS GUYS!!!
This is all great inforamtion! I have had the rear end and the parts trams for many years now, just had not had the time nor $$ to try to figure what was the best route to do the swap. I am also thinking since I love to drive my truck so much, that this may be the time to do the front disc brake thing... Has any one done the Nissan Hardbody trick front disc brakes??? Thanks In Advance, Garry

I have a Task Force ('57) third member. Will the axles on my '49 1/2 ton fit it If I put it in?

Stingray, that's exactly what I used, a '57 pumpkin into my '49 carrier and axles. I did burn off the pivoting perches from the housing and replaced them with perches from Buffalo. He supplies a spacer so that your wheels are located in the center of the wheel wells.

It only drops you from 4.11 to 3.90, but I have an overdrive tranny that is .70; the math, .70X3.90 = 2.73 final drive in overdrive, I cruise 65-70 mph at somewhere around 2000 rpm's.

Dusty, I don't know if it's the same for your '46 housing.

Just completed swap on my 51. used a blazer rear ,343 ratio,and saginaw 4speed, from a camaro, now I can drivr sixty -five or so with no strain.also went to duel master cylinder,Truck is real fun to drive now.