Question on the Durango differential fluid change

[rohan]

Dealership told me I needed to have the fluid changed in both diffs because the "additive" Dodge  uses in the light truck which they say are all the trucks lighter than the 2500 breaks down every 15,000 miles.  It's also $250 bucks to do it.

Is there any truth to it or is it bs? 
What's the "additive" they use?
Can I get it anywhere and have someone else do it?

[280Z Turbo]

What does the owner's manual say?

[rohan]

It says what the dealership says - but I'm just finding it hard to believe it's really a problem.  I've got about 65k on it and it's never been done before.

[3.0L V6]

I know Dodge had some issues with the Dana differentials in their Ram pickups, but I haven't heard anything about Durangos.

[S204STi]

If the dealership recommendation jives with the owner's manual then there is without a doubt a need to perform the service.  You could save money by buying whatever additive they use and doing the service yourself, using the additive and whatever viscosity gear oil is recommended in the owner's manual.

The additive is most likely just for the rear differential, which may be a clutch-type limited slip.  Those require friction modifiers to prevent them from locking up before their designated threshold.  This can cause catastrophic failure of the rear differential.  Unless the front diff is also limited slip, which I find highly questionable, you don't need the additive for that one.  Just use plain gear oil.  The transfer case fluid may also require periodic replacement, check the owner's manual for intervals and fluid recommendations.

[rohan]

How do you know if the fronts limited slip or not?  And thanks guys.

[S204STi]

How do you know if the fronts limited slip or not?  And thanks guys.

That is harder to tell, but a basic mechanical method is to lift the front end off the ground and spin one front wheel.  I think you might have to have 4wd engaged.  If the other wheel turns the opposite direction, then it is not a limited slip.  But if they turn the same direction then you do in fact have a limited slip.