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Discussion Starter · #1 ·
Hi, I just purchased a '05 Rubi and I have a couple of quick questions concerning the rear differential oil - especially friction modifier.

First, I drained and put in 75W-90 in both differentials. I'm not towing, so this should be fine, but I found it strange that the service manual stated that for the Rubicon 216 (model 44) to use 75W-140.

Second, and my main question is that I'm trying to figure out the rear differential (I'm a newbie). So I understand that the rear Rubi Dana 44 is a 'tru-lock', locking axle with a gear driven limited slip. So does that mean that I need to add friction modifier to the oil? In the manuals, it keeps referring to adding that to the trac-lock axles.

Thanks for the help,

Wes
 

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Discussion Starter · #2 ·
I think that I answered my own question. I read the service manual describing the rear differential and it states that it when it's not locked it acts as a standard differential, i.e., it's open not limited slip in any capacity.

Wes
 

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The FM is for clutch type LSD's, not what you have in the back of your Rubicon. Anyway, most of the modern gear oils come with the FM in it already, they say compatible with LSD on the bottle.
 
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