The Stovebolt Site Forums The Shop Area Driveline 37 GMC Rear end

I have found it very confusing regarding the gear upgrade from 4.11 to 3.55. For the 37 I am told by the ring gear supplier the ring gear is riveted on, so the actual carrier must be changed as well by substituting a 48 to 50 center and modifying the tube length and spline at the yoke. I know I can get a rear out of a 49 to 54 car with a 3.55 and modify the mounting to get that to work, but do I have to modify the tube length and yoke spline from a 49 to 54 to fit the 37?

Starting in 1940 the splines became finer in passenger cars and trucks on the drive shaft.

Patrick's 3.55 gear set for trucks will not work in anything earlier than 1940 as that was the first year for hypoid rear ends in trucks. You would need a 1940 or later 1/2 ton torque tube, axle housing and axles for his 3.55 set, then there is the spline issue, but that can be overcome.

If using a 50-54 pass 3.5 you would need to use the hole assembly including cross axle housing. The length of the torque tube may need to be changed. There is still the spline issue but that can be overcome if you go that way. You may also want to install 1940-48 axles to stay 6 lug.

To get past the spline issue you have a few choices. You can change to 1940-46 gears in your 37 trans(if a 3 speed), use a conversion U' joint(I have some, and they show up on eBay), or change the female end cap on the rear of the drive shaft to fine spline.

Lots to think about.

That helps clear up some of the confusion. I will have to see what parts are available and then figure out the correct path. I I am having trouble tracking down a 50 to 54 rear at a decent price. Not too many old junk yards on my part of New York.

I did not understand the spline issue and I will have to try to get a conversion u joint, sound like I am going to need it.

Thanks!

The conversion joint is not advertized as such.
It is just that some of the first joints made by aftermarket companies used the old design, (how they bolt together), for the new fine spline assemblies.
This allows you to use the new fine spline rear yoke with your front yoke.

Mike J 37 GMC -
I have done all of that with my 37 Chevy pickup. I wrote an article that appeared in "The 12 Port News", the Inliners International club magazine, some years back. If you want a copy, drop me a note at: [email protected]
In addition, I have some other information that may be helpful.