For you Buick Torque tube guys that’s want to change gear ratio

Here’s some info for those Buick guys who want to keep their straight 8 and torque tube rear.
My 48 Special have a very low 4.45:1 gear ratio from the factory and I was lucky to find an axle from a 1950 Super with Dynaflow. The gear ratios on the Dynaflow equipped cars are often 3.60:1 and I think this one will be perfect in my 48. The Buick differential carriers are interchangeable from at least 1940 up to 1955. 1956 they got more numbers of splines and are another story. This ratio will lower my rpm from nearly 3100 to 2400 rpm in 60mph.
Here are some pics from the transplantation


This is the rear axle from a 1950 with the right gear ratio inside.


They have the ratio marked by numbers on the ring gear. In this case 47-13 is 47 divided by 13 = 3.60


First remove the lock screw


Take out the shaft


The pinion spacer is located between the inner ends of the shafts and controls end play of axle shafts and have to be removed. Then push in the axle shafts to get access to the c-clips.


Remove the c-clips by knock them in and let them fall out in the housing. I have to make this simple tool to knock them out.


Take the axle shafts out.


The propeller shaft is connected to the pinion through a splined joint and a pin. Knock the pin out and remove the propeller shaft.


Cleaning up the housing.


Now ready to put back in.


The 3.60 carrier in place with new gaskets.


And finally sliding the torque tube back and connect the control arms to the axle again. Connect the brake lines and that’s it.


And finally my 48 Special with the rear axle in place.

I hope that someone can find these pics useful if they’re planning to do this transplantation.

 

nice tech and important knowledge for new owners of older Buicks. I believe there is an even lower ratio available. Seems to me it came on the Supers and Rivs around 53

 

Yes your right. I think you can find 3.20 and 3.40 too on those later one’s.

 

55 Centurys have a 3.42,other year Centurys back to 37 may also. Rich

 

Was all that trim on the fenders a factory accessory as I never seen a Buick with it before,I know the Chevys had something like that.

 

1940-55 is a nice swap. 1937-40 is more work with part interchanges. Pre 36 on the Specials is a no go. Pre 36 on the super-Roadmaster is hard.

Fritz

 

My '55 Special has 3.36 gears.

 

Thanks, that´s interesting!
Can anyone tell me the gear ratio of a 1953 Model 40 Straight 8 3spd vs a 1953 Model 50 Super V8 with Dynaflow? A friend has a 53 Buick with the straight eight, and a little higher gears wouldn´t hurt. Another buddy has converted his 53 V8 to TH 700 and open drive, so that´sthe center section we could use in the straight 8 53...

 

1953 40 series 1st and 2nd type with 3-speed = 3.9:1
1953 50 series 1st and 2nd type with Dynaflow = 3.6:1 standard
1953 50 series 2nd type with Dynaflow = 3.2:1 optional

The axle should be stamped on the bottom of the center of the axle housing with the ratio:

3/2 = 3.2
3/6 = 3.6
3/9 = 3.9

Sorry, I don't know the difference between the first and second types.

 

nice write up

 

How did you get the drive shaft coupler off the pinion? How did you get it on the new pinion staaight? Repair manual says it takes dealership tools. I tried years ago and I couldn't budge it.

 

Older post but great info

 

I just picked up a 3.58 gear set from a 55 I’m planning on putting in my 1950. Also using the 1955 brakes.