Originally Posted by desert_sand
Many thanks guys. Your advice was 100 % correct. After the dealer changed all the diff and trans case fluids - no more growling noise.( about $500. later )
Looks like the previous owner had taken it somewhere where they had put in the wrong fluid. Is the Jeep unique in needing this special fluid ? Would it be better to keep getting the dealer to do the 4 X 4 service, to ensure they use
the right stuff ? How often do these fluids need to be changed ?
It's not necessarily the gear oil/fluid, as it's the additional friction modifier that's needed to prevent the Vari-lok/LSD's from binding during tight turns. As others have mentioned, you can read more about how the Vari-lok differentials function in you WJ by going to WJJeeps.com
That being said, $500 is a lot of money to spend on having two differentials serviced. I'm not aware of your mechanical ability or know-how, but a differential service can easily be done in your driveway with basic hand tools. Even if you had to buy a basic mechanic's tool set, you likely would have been under $200 in tools and fluids (depending on how crazy you wanted to get on your fluids).