Diff Oil and FM

[Justino]

I have recently replaced the diff oil as part of replacing the input shaft seal due to a light oil leak. I used Castrol Syntrax for LSD's rather than the BMW version, the only difference is the BMW Castrol includes an FM or friction modifier. The FM is to reduce any diff noise in slow speed tight cornering where the diff plates can bind apparently, and is not essential other than to reduce noise.

Anyhow, without the FM I have no noise at low speed, but at higher straight line speeds I have detected a slight whine. I am wondering if this is connected?

Has anybody else experienced this using non FM diff oil. I can easily rectify by adding some FM (Redline FM), but wanted to canvas opinion before doing so.

 

[Beedub]

as long as its full to the top i wouldn't worry, the friction modifier by its very nature is stopping some of the effectiveness of the unit, as you say its only their to stop the noises a true LSD makes.... if i can get away without using any in mine i will do be doing so for sure.