Changing diff fluid, do I need LSD additive?
 

Getting ready to change out diff fluids, just wondering if i'm gonna need the LSD additive or not. I'm using Valvoline SynPower 75W90 full synthetic for the diffs.

Yes, you need the friction modifier even if the oil you are using says it's for Limited Slip diffs.

What if you use Royal Purple 75w90?

If the gear oil says it's for use with LSDs, you do NOT need to add anything to it. It already has friction modifier in it if it says it's comparible with LSDs. Too much friction modifier can make the LSD not function properly.

Thats what I thought I heard somewhere else too Redneck. This Valvoline stuff says... "recommended for all standard and limited slip hypoid differentials (conventional and high performance applications) including those found in passenger cars, light trucks, sport utility, heavy load, luxury and high performance models, API Services GL-5, MT-1" Just don't want to use additive if its not needed, sometimes too much of a good thing isn't good.

About the change mine as well and was wondering the same... I read somewhere before that if you use synthetic for use with LSD (I was planning Mobil 1) you don't need the friction modifier/addiditive, but never seen this confirmed by anyone with Chrysler/Jeep insider-info/knowledge.

The oem stuff with oem friction modifier doesn't perform near as well as a normal synthetic gear oil based upon the test results I've seen... in fact it was near the bottom of the 15+ gear oils they tested.

Check out WOL's write up for diff service...

http://project-jk.com/jeep-jk-write-...hange-write-up

Note on the left of the page, says you will not need an additive as long as you have a good synthetic.

I just called Valvoline tech line and they told me that the oil already contains a certain amount (forgot the percentage) of the LSD additive used in Trac-Lok/LSD systems and that unless I want to run an open diff not to add any more.

I run the Valvoline full syn. 75/90 front, 75/140 rear... no adds....
no problems...

According the the manual... if you have tack-lok, you have to add an additive, but it does not say what kind. I have the e-locks on both frount and back, so don't one need to have the addative for the lockers?

Don't quote me on this because im definitley not a mechanic but I don't think Rubicons require an additive. The Trac-Lok is a clutch type LSD and requires a friction modifier for the clutches, Tru-Lok which is used in your Rubi is gear driven so I dont think it would require an additive.