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Fluids be expensive

Mr._Bill

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So i just picked up my Overland had a gear change, at 500 miles i decided to change the gear oil so i went with royal purple synthetic i have a rear limited slip & the gear shop said my limited slip was half warn down I’m at 13,400 miles. He said synthetic allowed too much slip & wear . For me to use conventional gear oil with limited slip additive. It’ll do better.
Synthetic should not be a problem. The limited slip additive needs to be put in, unless the fluid is formulated and labeled for use in limited slip differentials.
Something like this should work well. https://smile.amazon.com/dp/B00B9XDOLO/ref=cm_sw_r_cp_apa_i_w4Y7Eb1T694D6
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Synthetic should not be a problem. The limited slip additive needs to be put in, unless the fluid is formulated and labeled for use in limited slip differentials.
Something like this should work well. https://smile.amazon.com/dp/B00B9XDOLO/ref=cm_sw_r_cp_apa_i_w4Y7Eb1T694D6
I know that’s what i used it was Royal Purple full synthetic labeled that additive was not needed. I’m just sharing what my Gear guy said with over 30+ years of experience with gears.
 

LostWoods

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Synthetic should not be a problem. The limited slip additive needs to be put in, unless the fluid is formulated and labeled for use in limited slip differentials.
Something like this should work well. https://smile.amazon.com/dp/B00B9XDOLO/ref=cm_sw_r_cp_apa_i_w4Y7Eb1T694D6
Some synthetics do weird things with Trac-Loc rear ends. The spec is for viscosity and lubrication but that doesn't mean it behaves well with clutch-type LSD units - they will often slow or speed up engagement.

In addition to the wear issue, this is largely why I never recommend them... a Torsen/Eaton style will be far more effective without the weirdness that can come with different fluids and they don't wear in the same way. There isn't an option for these trucks yet (which blows my mind now that the JL is in its 3rd year on market) but I'd definitely pass on the OEM one and just eat the cost of an aftermarket unit up front because it will be far cheaper if you plan on keeping the truck.
 

Texops

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Some synthetics do weird things with Trac-Loc rear ends. The spec is for viscosity and lubrication but that doesn't mean it behaves well with clutch-type LSD units - they will often slow or speed up engagement.

In addition to the wear issue, this is largely why I never recommend them... a Torsen/Eaton style will be far more effective without the weirdness that can come with different fluids and they don't wear in the same way. There isn't an option for these trucks yet (which blows my mind now that the JL is in its 3rd year on market) but I'd definitely pass on the OEM one and just eat the cost of an aftermarket unit up front because it will be far cheaper if you plan on keeping the truck.
for sure the Detroit Lock rite or whatever they call it, is gear driven & that is what i want some day when it becomes available for the JT,
 
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So what mileage should diff fluid be changed? Im not seeing it listed in the user manual
 

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Riccochet

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I change diff oil every 30k in my Ram's. But, my Ram's see about 75% towing use. Blackstone says the gear oil is still good, probably for another 10-15k.

I change the diff oil in my JKR every 50k. Blackstone came back good as well.

Royal Purple 75w140 in both. Better shock load protection with the higher hot weight. I do add a little friction modifier to the Ram's. Not needed on the JKR.
 

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The book does indeed say what you should do, but couches it under a bunch of conditions. Among them are off-roading or frequent trailer usage. I would follow that schedule, which is 40k miles. It also says to inspect every 20k. Basically that means taking a little off the bottom and checking for water or other issues. Changing fluid every 40k is plenty, as proven by oil testing.
 
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The book does indeed say what you should do, but couches it under a bunch of conditions. Among them are off-roading or frequent trailer usage. I would follow that schedule, which is 40k miles. It also says to inspect every 20k. Basically that means taking a little off the bottom and checking for water or other issues. Changing fluid every 40k is plenty, as proven by oil testing.
oh ok, so the axle fluid is the same as the differential fluid.
I wonder how much "off roading" or "frequent towing" warrants the interval. Out of 27,500 miles I would say i have 500 miles off pavement in actual off roading conditions (rocks, creek crossings, mud ruts/holes). Given the offroading is grouped with the police/fleet uses I would assume offroading would have to be a principle use
 

SwampNut

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If you do the inspection interval at every 20k, maybe you can just see how the fluid is doing. I don't use exotic/expensive fluids since the evidence is that there is no advantage, so I'll just change it every 40k anyway.
 
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If you do the inspection interval at every 20k, maybe you can just see how the fluid is doing. I don't use exotic/expensive fluids since the evidence is that there is no advantage, so I'll just change it every 40k anyway.
But what do you look for? JL forums are saying "such and such looks bad" but apparently analysis reports show that's ok. I have heard of metal shavings being ok, and not being ok
 

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SwampNut

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I look for water, which in diff oil is usually something milky-gray-brown depending on the specific fluid. A very tiny bit might be fine, but not any appreciable amount. And a tiny bit of metal wouldn't bother me. I don't really know how to express the amount that would make me worry, but it would be pretty obvious. I've been working on cars for 40-some years, a lot of things are just gut feeling. Overall, it's extremely unlikely for any of our JTs to have bad oil at only 40k miles.
 

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Visual inspection, outside of visible water, is pretty pointless. It doesn't bear any indication on the actual condition of the oil.
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