kevin2012

I am thinking to switch to Fuchs 90LS for my PSD diff. It says that it has the friction modifier. Has anyone use this before can give me some comment please?
Currently, I am currently using Redline 75w90 synthetic oil.
As my another post saying, I am having a rear end whining noise and likely from the diff, I am hoping by changing the right diff oil can reduce the noise a bit.

91S4

dr bob

Kevin -- I'm not sure you need or want friction modifier with PSD. "Friction modifier" is often graphite or moly powder added to reduce the grab on the LSD clutch disks so they don't chatter going around corners. On the PSD car, the clutches are engaged hydraulically, and only when needed. By the time the PSD controller determines you need some differential lock, it manages the slip by varying pressure on the clutch pack. No chatter in my experience.

If you are hearing diff whine that changes between leading and trailing throttle, you may want to pull the box and do a full inspection to see why. Try new oil first of course, and look carefully at what comes out.