[balmo]

if you use diff oil like red line or royal purple, you do not need additives since these have friction modifiers already. i use additives on my track car (100% lsd lockup). plane jane gear oil plus sta lube friction modifier.

 

[Lscman]

Limited slip additive has one purpose. It reduces initial clutch breakaway torque, providing a more linear overall power transfer behavior. A high breakaway torque characteristic is sometimes referred to as stiction and it occasionally causes dealerships headaches from frivilous customer NVH complaints ("...I hear a noise in the rear of my car...hope it's not broken"). Performance drivers (with low torque pedestrian OEM clutchpacks) who want good 2 wheel traction should avoid these additives like the plague. Stiction (high breakaway torque) is what helps you churn both tires at launch or turn hard under acceleration. The additives reduce LSD clutch grip which adversely impacts the effectiveness of your limited slip clutch assembly. This encourages one wheel to spin under hard acceleration (more like a conventional open differential) which impedes acceleration and can reduce LSD clutch pack lifecycle.

PS: This recommendation does not apply to all racing diff's with LSD's, as they sometimes have extremely aggressive clutchpacks that require such additives to manage severe wheelhop, chatter or push/understeer symptoms.

If an LSD clutch chatters unacceptably, then you try some additive to manage it. Almost all hypoid diff lubes have enough additive in them already to manage stiction in an OEM LSD.

hope this helps

 

[mudmojo]

PS: This recommendation does not apply to all racing diff's with LSD's, as they sometimes have extremely aggressive clutchpacks that require such additives to manage severe wheelhop, chatter or push/understeer symptoms.

Good explanation. I had a ruckus in a brand new tight STI plated rear diff that would act up on tight turning circles and that one could hear from over two busy city blocks away. It was extremely annoying and scrubbing tires like it was welded shut. Sounded like someone hammering on plate steel.

Not all of these lubricants will work unilaterally. I had the expensive Motul FF (WRC spec) gearoil in and that didn't slip enough so it was still noisy.
Subbed in some Redline Heavy Shockproof and that noise disappeared over the next few kms.

 

[havasusteve03Beast]

As previously mentioned, Redline or Royal Purple is a great differential AND transmission fluid. Since you recently purchased your car, congrats and thumbs up on changing the rear diff. fluid. Also need to change that tranny fluid REGARDLESS of what a dealer tells you. I have tried the BMW OEM stuff and it obviously works well but is very $$$$$. My personal choice is the RP which is available at most Pep Boys and is much more reasonably priced.

Good luck and welcome to the group

Steve