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Topic: Rear Vs. Front Axle Diff Lubricant

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Rear Vs. Front Axle Diff Lubricant
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I need to change the lubricant for both the rear and front axles. The FSM tells me that I need to use SAE 80W-90 gear lubricant. However for trailer tow what is needed is SAE 75W-140 SYNTHETIC lubricant. The tag on my rear diff also corresponds to the part number for the SAE 75W-140. I am in the meantime building a trailer to use with the XJ thus will need to use the heavier lube.

SAE 80W-90 lubricants are readily available in my part of the world. However SAE 75W-140 is a rare sighting. I found Mobil SAE 80W-140 gear oil. However when i asked for "Synthetic" the shop attendant wondered what i was talking about!

Question is can I use the available Mobil SAE 80W-140 in the rear diff without any problems. I guess the biggest advantage synthetic has over the natural gear oil is longer life meaning I would perhaps need to do a oil change sooner than the recommended periods.

Any ideas? Thx in advance.

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choppergar
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I don't see any problem. I would use the 80w-140 in mine, because of the wheeling I do.

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Gar Pratt
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Are your inners stock (do you have lockers)? Do you have a factory Trac-Loc (limited slip in the rear)?

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LEAD_NOT_FOLLOW wrote:

Are your inners stock (do you have lockers)? Do you have a factory Trac-Loc (limited slip in the rear)?






Yes the intestines of the diff are stock. Sorry I dont know about Trac-Loc but there is a tag attached to the diff advising something like "USE ONLY LIMITED SLIP DIFFERENTIAL LUBE". That means i have factory Trac-Loc, right? What exactly does that mean and how does that affect the lube to be used??

Thx

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bmyohn
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that should mean you has a true-lok

you need a special additive i believe

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LEAD_NOT_FOLLOW
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If you have limited slip than yes you have the factory "Trac-Loc". It has a clutch pack in it and does require a special additive to help keep the clutches from burning up...

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LEAD_NOT_FOLLOW wrote:

If you have limited slip than yes you have the factory "Trac-Loc". It has a clutch pack in it and does require a special additive to help keep the clutches from burning up...

Thanks LEAD, thx bmyohn. And now for the inevitable question...... What is the Special Additive that I need. And back to the original question, would the available SAE 80W-140 lubricant do instead of the stated SAE 75W-140 Synthetic..... I see Choppergar says no problem but more responses to my query are welcome. I intend to do the change over this coming Easter weekend.

I will do more reading about Limited slip diff in the meantime as I do not seem to understand the issue without further reading/research. Thx guys. Ed

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bmyohn
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i know that when i went into NAPA i told them that i had an LSD in the rear and i needed the additive, they got me exactly what i needed.

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Extra friction modifier should not be added if the oil already has it in it; as that can cause the gears to run hotter and the LSD to chatter. The exact viscosity of the GL-5 gear lube is not as important as it being rated GL-5 or GL-6. If you live in a colder climate, choose a lower viscosity like 70W-80, 75W-90, 90, etc. If you tow, wheel in very tough environments or it gets very hot, a higher viscosity like 80W-120, 80W-140 etc. is recommended.

Personally, I now believe in using a non-synthetic gear lube for my axles with recent revelations that the gears run cooler in a non-synthetic gear lube than the do in a synthetic gear lube. That's probably not a big deal if you don't wheel in tough conditions but if you do...

Some gear oils have the friction additive already in it, some do not. If it does not you'll need to add 4 oz. of friction modifier separately.

Also for the record Trac-Lok is a limited slip clutch driven, True-Lok is a limited slip gear driven. From the factory on the XJ/MJ it came with a Track-Lok

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Thanks Adam. Mhhh what started off as a simple lube question has led me to new discoveries I didnt know about the Jeep. After more research I now understand about limited slip differential et al. Thanks guys.

As for the lube to use I have setlled for Mobil 1 (http://www.mobiloil.com/USA-English/MotorOil/Other_Products/Mobil_1_Fully_Synthetic_Gear_Lube_75W-140LS.aspx). Since the mobil 1 already has Limited Slip additives I wont need to look for the 4 ounces of friction modifier..... wink

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bmyohn
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the modifier is not hard to find. I would stick with whatever brand you like, then just tell the guys at the store you need the friction modifier for your axle and most likely they will have what you need in stock

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