I wanna go ahead and change the oil in both the front and rear differentials on my JK.
I saw the write up thread and figured I could do this myself however I have a few questions.

1. What type and brand of oil should I use?
2. Can I use the same oil on both the front and rear diffs?

And a little more info on my JK:
It is a 2007 JK, auto.
Basic package with out the tow package
I don't tow anything either.
Thanks.

 

I also forgot to mention its an X model.
And do I need to add some sort of additive to the diffs because I have read something like that here.
Thanks again.

 

Most folks here will recommend a synthetic oil. Each will have their personal preference, mine is Mobil 1. But, I think you'll be fine with any major brand (Mobil 1, Valvoline, Royal Purple and Amsoil, to name a few). You can use the same oil in the front and rear if you don't routinely tow things. Here's what my owner's manual (2007) has to say about the diffy fluid:

Axle Differential (Front): Mopar Gear & Axle Lubricant (SAE 80W-90) (API GL-5) or equivalent.

Axle Differential (Rear): 198 RBI (Model 35) and 226 RBI (Model 44) - Mopar Gear & Axle Lubricant (SAE 80W-90) (API GL-5) or equivalent. For trailer towing, use Mopar Synthetic Gear & Axle Lubricant (SAE 75W-140) or equivalent. Models equipped with Trac-Lok require an additive.

Trak-Lok is the Jeep Limited Slip Differential (LSD). Even if you have LSD, most synthetic fluids do not require the additive. I've used both Mobil 1 and Valvoline (when the parts store was out of Mobil 1) and never had the chatter that suggests that I needed a friction modifier (the additive's purpose). Modifying the friction when it doesn't need it is not good for the differentials, so don't add additive unless you have chatter from the diff.

 

Just did mine last week...I went with the Mobil 1 75-90 full synthetic...front and rear. It has the additive in it already so I'm covered for that. If you do not have the LSD it won't matter to the gears...
Pretty straightforward job just a little time consuming filling back up with a plastic hose attached to the bottle...

 

Ok cool. I was thinking of going with The Royal Purple 75W90. Would this be good for both the front and rear?
And this may be a noob question but I would I know if I have the LSD. ( )
Do all 07 X's have this? Mine is 4X4.
Honestly I dont even know what LSD or Limited Slip Differential is.
I have been off roading a few times. Dont know if that changes anything.
Thanks.

 

Plenty of folks will attest that Royal Purple 75W-90 is a fine lube for your diffys--front and rear.

One of the weaknesses of a differential (an "open" differential, which is most common on vehicles) is that when one wheel starts slipping, all (or most) of the drive power goes to that wheel. Obviously, if you're trying to get moving on a slick surface sending all (or most) of the power to the wheel without traction isn't very efficient. So limited slip differential was created. If a tire begins to slip, then power is rerouted to the other wheel. However, that is not the most efficient for some situations. That's why lockers were created. In that case, basically the differential action is taken out of the equation and both tires are locked to rotate at the same speed.

Different models of Jeeps have different combo's of open diff's, LSD and lockers on either axle. Chances are you have open diff's on both axles (because you have an X). However, some X's came equipped with LSD on the rear axle, and a few lucky ones even have lockers on the rear axle. If you have a locker switch on your dash, then you can lock your rear axle. No special lube required for that, BTW. To determine if you have LSD, jack up the entire rear of your Jeep. Hand turn one tire. If the tire on the other side rotates the opposite direction, you have an open diff--no special additive required. If the tire on the other side rotates in the same direction, you had an LSD--special additive required, unless you choose a synthetic lube.

 

I bought a 1 gallon jug lucas oil to do mine. They make pumps for the one gallon jugs that you can usually find at any parts store. Attach some tubing to it and pump it into the fill hole. It's easier than messing with the quart bottles.

 

ive done both in royal purple 75 90, no problems just make sure you put the pan in the right spot when you drain it

i used a hobby fuel pump and cranked the fluid in from the bottle after trying to wrestle it in there with the bottle