I am planning to install a PML Differential Cover and need to make SURE that I use the correct formulation for the fluid replacement fill. I have the 9.25 LSD in a 2WD QC Hemi. My first choice for replacement oil is the Mobil One 75W - 140W Synthetic however I would go with Royal Purple or just buy the Mopar replacement synthetic; I've already purchased the Moparfriction modifier.

If I use the Mobil One do you add the friction modifier too? I've heard with the Royal Purple that you DO NOT add the modifier? Then others have said it is a 'trial and error' project for all syntheticsmeaning if you don't have enough friction modifieryou get chatter and if you add too much you lose the LSD functionality; even others have stated if you add the Mopar friction modifier to the M1 or RP you get a thick gel goo that screws the differential??? So what's the truth?

If you have done the modification that I want to do please provide clarification for my questions above; I just want to do it right the first time.

THANKS!
toxdoc

 

The Mobile 1 is probably much cheaper than the Mopar oil and will work just as good.

I suggest that you put in the new oil and DO NOT put in the additive and drive it some. After a couple of miles, if the rear doesn't chatter, go to a parking lot and make some tight figure 8's and see if it chatters.

If you get a chatter, add 1/10 bottle of additive and do it again, etc.

The reason is that the Mopar synthetic that is in there stock is super slippery. Add to that the slippery friction modifier and the clutches are already soaked in slippery stuff.

I have the same rear, different gears and I have NO additive in my diff. Its on the shelf in its brandy new plastic bottle. In fact, I have standard off the shelf 90W in my diff. I don't want the clutches slipping when I slam it from a dead stop. I have thousands of miles on it, no problems, no chatter.