I am about to change the fluids on both my rear and front diffs, and was wondering which one to use?
I was gonna go with the Royal Purple Max Gear 75-90 but on the bottle it says it has added friction modifiers and something Synetec additive ( I have no idea what these are). Anyway my question is can I use that one? I have heard not to use any with any additives. I have an 07 X.
Thanks.

 

Do you have Limited Slip Differential in rear?

 

Most all synthetic gear oils have friction modifiers. If you have a limited slip rear then you need friction modifiers.
If you don't have limited slip, you can still use it with no ill effects.

I use it and don't have limited slip, I have lockers.

 

Nah I dont have a limites slip or any lockers, just the stock that came from the factory.
Anyways ya ok Cool, I'll just you that one , thanks.

 

Royal purple is good stuff I run it in my front open differential.

 

Use Royal Purple for engine oil, diffs, transmission and transfer case. Use the Royal Purple oil filter too. I aim to keep my Jeep for a long time and I did a lot of research, talked to quite a few people. Eight out of ten folks I talked to agreed that Royal Purple is the way to go.
It's higher, but it's cheaper in the long run.

 

With all due respect I run Royal Purple in all my stuff, my JK, Excursion, and all my ATVs. I did run into one problem with it in my rear of my JK and that was after about 30K miles on my new gears my factory L/S was toast. The clutches had worn so bad ly that my spider gears chewed themselves up. After talking with the Brian at Northridge we came to the conclusion that chances are the Royal Purple gear oil..though it sayd it has friction modifiers in it, it probaly wasn't enough. So...I replced the rear diff with a grizzly locker, fillled it back up with Royal Purple and all is good. If I had to do it again I would of just added a small amount of friction modifier just to be safe.

I'm not at all knocking Royal Purple, I love their products I'm just saying that sometimes what they have built in might not be enough and to be careful. The interesting thin is I had no outward signs or symptoms that anything was wearing improperly. We actually found it when I was doing a service to my diffs and trans. Which all were refilled again with Royal Purple.

 

LUBE LOCKER
If you haven't changed the oil yet you might want to think about using "Lube Locker" instead of RTV silicone. They are expensive but reusable, faster and cleaner to install, and supposed to stop seeps better. That's what I'm going to use when I do mine.

POINTS TO CONSIDER
I have heard that synthetic oil is slightly more prown to seeping because of smaller molecules? Then again that could be BS. I have also heard if you wheel pretty often your most likely not going to need the extended life, because of more frequent oil changes after playing in water.

ADDITIVE
If you have factory clutch plate LSD aka Trac-lok aka anti rear spin differential option you need the additive. If your not sure then a synthetic with the additive would be a good option but more expensive.

Does anyone have a recommended brand of non-synthetic oil?

 

Why lube locker? Can't all of us JK people change the diff fluid using the drain plug? No need to remove the cover therefore no need for line locker. (Unless you really want to open it up to look inside.).

 

I have used RTV in the past and that has always worked. This wont be the 1st time I change the fluids. But this time I am going to open up the diffs and clean it real well then apply it back on.
I know some people say you dont need to open up the diff covers that just to drain it, but I feel better if I do, plus it will show me if any signs of wear and tear. Any way I bought the royal purple 75-90 Max Gear and plan to use that.