4th Gen Rear Axle Fluid

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La Ramie

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So my 2013 4x4 comes with 3.55 rear axle w/o limited slip.

Looking at 2013 owner's manual, the fluid for the rear axle should be 75w-140.
But looking at 2022 Classic owner's manual, the 3.55 uses 75w-90, and 75w-140 should be for 3.92.
That's a big difference in viscosity between 75w-90 and 75w-140.
Since the front axle uses 75w-85, it would make sense for the rear to use also 75w-90. This way I can buy the oil in boxes, which is cheaper. Yes, 75w-85 and 75w-90 are interchangeable.

Did Ram change the rear axle?
I know the transfer case was changed after the change to 8hp from 65rfe but I wasn't sure about the rear axle.
 

crash68

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Rear axle is the same since '11 when they changed to the ZF 9.25".
More than likely the heavier oil in the 3.92 is for anticipation of people towing with their trucks. If you don't tow or do very little/light towing then the 75W-90 is probably fine to run in both front and rear.
 

zogg

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I believe 2017 was the last year mopar recommended the 75/140 oil. 2018 and newer get 75/90. I’ve been researching this to change my own oil. I can’t find out why the change but just that they did. Goofy. Might be for + mpg but I’m not certain
 
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La Ramie

La Ramie

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The language and type of oil have also changed when it comes to the recommended oil for the 5.7HEMI.
 

Jeepwalker

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Edit: delete
 
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