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I'm buying my '05 Rubicon at the end of the week, yay! I'm going to change fluids right away. I downloaded the '05 TJ service manual, and I have a choice for the differentials between 80w-90 or 75w-140 (towing). I'm not towing anything.

So what's the fluid recommendations? Just looking at amazon (royal purple) and amsoil, 75w-140 is readily available. Is it better or safer to go with 75w-140 even if no towing, but some climbing?

This will be my DD, but I'm 4 hours from Moab, so I'll be having lots of fun there too.

Thanks, this forum rocks,

Wes
salt lake city
 

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The exact viscosity is not all that important where a differential is concerned. If you do some tough offroading, there's no reason you couldn't go for the 75W-140. Personally, I prefer a conventional gear lube inside my axles since a conventional gear lube has been shown to keep the gears cooler than a synthetic. Custom axle manufacturers like Currie even require their customers run a conventional gear lube inside their axles to keep from voiding the warranty as would happen if a synthetic was used instead.
 

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You should run conventional in the diffs. The diffs cool by the oil transferring the heat and conventional does it better. As far as the weight i have always run 80w-90 but either would be fine.
 

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I was told by a trusted mechanic to run amsoil synthetic. From his own racing experience of over 20 years he found Amsoil synthetic gives the longest life to diff gears. He told me the steep gears they were running they would only get one or two races on a set of gears with traditional oil. They experimented with different gears and oils for many years until they started using Amsoil. He said after they switched they would make it a full season on a set of gears. When he installed new gears in my front end he recommended this to me. I cant explain the whole process like he can, but for me it was a no brainer when someone with real experience recommends this over some company trying to sell there product.
 

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I am getting ready to do this same job on my '05 TJ. She is an X with 3.73 trac-lock limited slip. I have been searching forums too. Read good reviews about Royal Purple. Also read that if I use Lucas, I will not have to worry about the friction additive. Also going to change out rear stock cover to ARB cover to match front. Anyone confirm this info......thanks!
 

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Also read that if I use Lucas, I will not have to worry about the friction additive.
Nearly all gear lubes you find on the store shelves contain the friction modifier additive needed by a Tracloc. It is hard to find GL-5 gear lubes that do not.

If the back label has words to the effect of 'Compatible with limited slip differentials', that means it contains the additive.
 

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P.S. The reason most gear lubes have the friction modifier additive is that it is safer to include it for all the clueless people who don't know they have a clutch-based limited slip differential.

The additive is compatible with virtually all differential types whether or not they contain a clutch-based limited slip differential.
 

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The shop wear I had my differential oil changed, would only add synthetic 75-140 in the read because I have a trailer hitch/tow package. I ended up with Royal Purple 75-90 in the front and 75-140 in the rear diffs. According to the manager, they have a barrel of RP for the Border Patrol vehicles. I forgot to ask him how often the BP has the diff fluid changed.


I am getting ready to do this same job on my '05 TJ. She is an X with 3.73 trac-lock limited slip. I have been searching forums too. Read good reviews about Royal Purple. Also read that if I use Lucas, I will not have to worry about the friction additive. Also going to change out rear stock cover to ARB cover to match front. Anyone confirm this info......thanks!
 
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