So I am thinking of changing my differential fluid. I have heard that you need to put an additive in if the axle has trac-lok which mine does. So my question is if an additive is needed if so what kind and where do I get it. THANKS

 

I got mine from Partsource along with my Sythethic Diff Oil, I believe most trac-lok are basically the same, just different brands. Most shops that sell Diff oil should carry it.

 

If you're going back in with dino, Mopar sells the additive. If you're going back with synthetic, you can get most of them with the additive already in it. Just look for the LS on the bottle.

 

OK here is the skinny on friction modifier... I did a lot of research on this when I did my rear diff on my liberty a couple years ago. There is a lot of myth and misconception when it comes to friction modifier.

Basically your gear lube has to have the right "slipperyness" (the official term is probably something like friction coefficient, but I like slipperyness ). Friction modifier makes your gear lube more slippery. You don't want your gear lube too slippery, and you don't want your gear lube to be not slippery enough. There is a correct amount of slipperyness and it probably varies between the different manufacturer's limited slip differentials.

If your gear lube is not slippery enough, your limited slip clutches will be "grabby" and won't want to slip. The result is when you turn corners on dry pavement you'll get chatter and feel a vibration. In a semi-slippery condition (wet pavement) going around a corner your limited slip may stay locked longer than it should resulting in the rear end kicking out. So it basically results in poor and unpredictable pavement manners and will wear your limited slip clutches out prematurely.

If your gear lube is too slippery your clutches may have a much harder time locking up. So depending on how overly slippery your lube is your limited slip may deliver a reduced amount of torque to the non-slipping wheel. In really bad cases your limited slip may act like an open differential because the lube is so slippery the clutches are completely ineffective.

So how do you know what the right amount of slippery is? If you are using the Mopar gear lube or a dino gear lube without friction modifier already added, it's easy. Just add the recommended amount of Mopar friction modifier (I think it's a 4 ounce dose).

If you are using a synthetic gear lube (like Mobil-1) they say you "MAY NOT" require any additional friction modifier. That's because their synthetic lube is pretty slippery all by itself. However notice they say "MAY NOT". That's because every manufacturer's limited slip requires a different amount of slipperyness. When I put Mobil-1 synthetic gear lube in my Liberty it ran fine for a few days. When the clutches had become totally impregnated with the Mobil-1 I started getting chatter and had a few unexpected rear-end kick outs in wet weather. I could have put a full dose of friction modifier in, but that could have then pushed it into the "too slippery" range. So what I did was add 1/4 dose at a time and drove for a couple of days until the chatter went away. That's when I knew I had achieved the correct slipperyness.

So basically either use the Mopar fluid (or dino with no modifier already added) with 1 dose of friction modifier. Or use a synthetic with no modifier added and if you find you need modifier add it slowly over a few days until your chatter goes away.

If you use an aftermarket lube with friction modifier already added, there is no guarentees. It could have too much, too little or just the right amount. Too little is easy to solve by adding more. Too much will reduce the performance of your limited slip.

 

Doc D - Thanks for the great explanation. That understanding is really helpful. I'm guessing that slipperiness is really shear viscosity, but slipperiness pretty well says it all.

Now I need to get under the Jeep and get those diff covers changed.

 

So here's my next question when I called Jeep they said that I had a no spin axle in the rear, is this the same as trac-lok? When my tires lose tration I can feel the axle distribute the power to both back wheels and the traction control light comes on. Do I still need the additive if they are not the same types of axles?

 

You need to look at your window sticker if you still have it. It gets a bit confusing in today's world of computerized jeeps.

All JKs have a feature that is sort of a simulated limited slip. Even if the rear differential is an open diff, the computer will apply the brakes to a silpping wheel to transfer torque to the opposite wheel. That's probably what you are feeling. The light you are refering to on the dash also indicated this is taking place.

Some JKs also came equiped with a mechanical limited slip (i.e. a trak-loc). You most likely shouldn't "feel" the trak-loc if you have it. If you have the trak-loc you need to add friction modifier to the Mopar (or dino) gear lube. You MAY have to add modifier to synthetic gear lube if you find you have "chatter" while turning corners on dry pavement.

The easiest way to determine if you have the mechanical limited slip (trak-loc) is to check your window sticker and see if "trak-loc" is listed. I wouldn't trust asking the dealer.

 

Just run lockers and eliminate all this foolishness.

 

Hey man just let me borrow a couple of grand and I'll get right on that. Just kiddin

 

you should also be able to give the dealer your vin# and they can look the jeep up and tell you what it came with from the factory.