Rear Axle Ring and Pinion compatibility issues

[Stang84g]

I am currently rebuilding a rear axle that I pulled out of my 1938 1/2 ton pickup. The ring and pinion that was in the truck is a 4.11 ratio and I wanted to put a 3.25 ration set in there to get better cruising speeds without running the engine too hard. It appears that this rear axle came from an earlier vehicle because it has the hollow tube driveshaft with a 10 spline couple and input for the pinion instead of the 6 spline that should have been standard on a 1938. I ordered a 10 spline - 3.25 ration gear set, and now the bearings on the pinion don't work. The new pinion has a smaller shaft diameter than the pinion that came out of the rear end. It is my understanding that the 10 spline setup was from 32-34, which did use a different bearing and cone set where it is two separate bearing race cones vs. the later integral double cone bearing race setup. My question is why did the 4.11 pinion that was in there have the larger diameter shaft with the double race setup and 10 spine, and if I use the bearings from a 32-34 setup, will that work in the banjo housing that I have? Do they have the same OD and length of the bearing kit? Where did this 4.11 setup that I have come from, and why do I not find any mention of this configuration in any of the research I have done?

[Brian]

The 4.11 you removed will be from a 35-36. Larger, longer than 32-34 style. Apart from the 10spline/6 spline difference, all other dimensions would be the same 35-48.

[Mart]

The pinion you have is only compatible with the (late)32-34 centre section. As Brian says, the bearing area is shorter and smaller diameter. It will not work in your centre cestion, unfortunately.

I don't know if a 10 spline gearset is available for the later axles in that ratio, you might have to go with a 6 spline gearset and adapt your driveshaft (difficult to find a lathe long enough) or swap in a 37-40 torque tube and driveshaft.

[JSeery]

3.25 is a steep gear for a pickup! Have you looked at tire size to reduce engine rpm?

[rotorwrench]

I would not recommend the 3.25:1 ratio for a commercial pickup. The 3.54:1 is about as good as it gets. Another alternative would be a Mitchel overdrive set up. This would give the lower number ratio for highway use plus the added extra gear.

You have to be careful to identify parts on these old vehicles due to the interchangeability. The 1938 model was a change over year. They still had a hollow tube drive shaft but it was an odd ball looking thing with taper out to middle and back in to the rear. The V8 was changed over from 21-studs to 24 studs in mid year.

The 1935/36 rear axle had radius rods that were a lot heavier and bolted to brackets welded to the axle bell tubes closer to the middle plus the spring hangers were part of the radius rod. The 37 & later axles had the spring hangers integral to the axle bell tubes. The 10-spline pinion was used till somewhere in 1938 or so.

This link used to have photos but it still has descriptions. https://www.hotrodworks.com/technica...axle-housings/
There was an old Hot Rod magazine article discussed here on the forum several times that had a hood photo spread on ID of the different rear axles. It was titled Treasure Hunt. If you do a Google search with "Identify banjo rear axle" it should come up. It has been here and on the HAMB.

[JSeery]

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Here is the Treasure Hunt article.

[Bored&Stroked]

You might want to talk to the guys at HotRod Works in Nampa Idaho - they can steer you the right direction and can modify what you have if that is the right approach (given your application, parts and gear ratio). They're great guys to work with.

B&S

[Mart]

For what it's worth, I have a 3.54 in my 41 pu with 6.50:16s. I used the lower ratio 15/29 gearset and it drives really nice.

[rotorwrench]

This type of problem comes up a lot due to the fact that they don't make the 10-spline replacement parts for the 1935 thru 38 cars. Even Ford switched over the the 6-spline pinion back in the day. They had spline adapters but they don't help on the hollow shaft much. Ford made the 68-4605-B shaft as a replacement part but it is a solid shaft. Some folks switch to the 6-spline pinion & ring set and modify the hollow drive shaft to work with it. This makes it a pain in the ahrs for certain but a fair amount of folks have found success doing it. Dick Spadaro, God rest him, had the front spline fabricated & put together the parts for a tube drive shaft kit for a while. It had a front spline shaft that welded into straight section of tube then the tube was cut to whatever length was needed and a modified 6-spline coupler was welded into the back. That kit was great for this type of stuff but no one has taken up the challenge to make them since.

[49r]

3.54 differential and 6:50 16's in my 49 pickup with a 265 8BA and heavy duty 3-speed gearbox. Having previously had 4.27 and 3.78 differentials fitted, I've found the 3.54 the best combination of low end torque and suitable cruise RPM.