Gen 3 vs 4 diff fluid

[MoparMap]

So I swapped out my gen 3 diff for a gen 4 a while back and am getting ready to change the oil in it. I know the gen 3 uses a friction modifier, presumably because the clutches for the locking setup use the diff oil itself as their lubrication. However, my understanding is that the gen 4 diff has a completely sealed unit that has its own internal fluid for the locking mechanism. Is friction modifier still required in this case since the clutches aren't in the diff oil? I always got the impression that was the only reason many of the different locking setups over the years required that special little bottle (helped the clutches work). Otherwise I don't understand why they wouldn't have the necessary additives in the oil to begin with if all you're doing it trying to lubricate the ring and pinion, but perhaps I'm missing something.

 

[Steve-Indy]

Gen IV uses same fluid as Gen III (and II and I)..as well as 4 oz friction modifier.

Gen V uses a different fluid.

 

[MoparMap]

Interesting. Oh well, I'm not one to discount factory design. Guess I'll try to pick up a few bottles of the stuff. Have several quarts of the diff oil already and was hoping I wouldn't have to track down the additive. I don't think it's that hard to come by, just annoying.

 

[Steve-Indy]

I remember a post about only using one 4 oz bottle of friction modifier in Gen IV differentials...just confirmed that with Tom Sessions.

 

[Kirkinsb]

I have a story for ya....the shop who put in my 3.55 gears knew nothing about putting in the friction modifier. And about 2-3 weeks later my diff really started barking at me and fighting me in slow tight turns. I added the modifier and now all is back to normal. So if anyone thinks friction modifier may not be necessary....I can assure you it IS necessary!!

 

[dirkbonn]

Thanks kirkinsb

I appreciate the headsup. I'm looking to buy a gen IV Viper and considering switching to the 3.55 gears as a first modification.