Does the rear differential have friction modifier?

[B-52Gunner]

Does the rear differential have friction modifier in it?

[SenorFunkyPants]

I'm pretty sure all differential oils for LSDs have friction modifiers...the Castrol Syntrax 75W140 (was Castrol SAF-XJ 75W140) certainly does.

The function of the FM additive is to allow the LSD clutch plates to slip smoothly against each other under low load (slow turns). At the same time, to allow the clutch plates to fully stick to each other when under higher load (accelerating through fast turns) - enables the diff to lock up and share the power between both wheels.
The diff oil needs to have the minimum possible amount of FM. Too little and the diff can be noisy in turns, too much and the clutch plates need a higher load before they can lock up.

I would say that the BMW Final-drive MSP/A gear oil has more FM (too much?) than the Castrol Syntrax.
I changed the diff oil in my car from the standard BMW Final-drive MSP/A gear oil to Castrol Syntrax 75W140.
Before the change, any hard acceleration in low gears and one rear wheel would spin up causing the DSC to cut in...now with hard acceleration in low gears the rear differential locks up and if traction is lost then both rear wheels spin. Result is way better traction.

[B-52Gunner]

Thank you for the info.

[heckyeahbro69]

SAF-XJ+FM Boosted oil (P/N 83 22 2 282 583) is designed specifically ONLY to be used in the previous generation M3 (E90/E92/93) vehicles.

For the F87, F80, F82, F83 vehicles, ONLY use:

Synthetic MPS/A BMW Final Drive Gear Oil (PN 83 22 2 357 992, 1 liter)