Castrol differential oil with friction modifier

[Hacra]

Hey all, there are multiple threads on this board about different oil types for different differentials and in most cases the discussion ends to recommend 75w140 oil + bottle of friction modifier.

Now this got me curious; are there any oil(s) with the friction modifier already added, so i mailed directly to Castrol and asked them if they would have anything like that available.

Below is the mail (their answer).

Thank you for contacting Castrol North America.

The purpose of the differential gears that are present in on-road drive axles is to permit each wheel to turn at a different speed than the other to prevent “wheel skip” when the vehicle is turning. Unfortunately, this causes conventional rear-wheel-drive axles to have a disadvantage when one wheel is on a slippery surface. All of the torque gets transferred to this wheel resulting in wheel spin, while the other wheel and the vehicle do not move.

One of the more common ways to remedy this issue is to build the axle with a clutch mechanism which senses when one wheel has reduced torque from being on a slippery surface and routes torque to the wheel with good traction. This clutch mechanism requires a gear oil having a lower coefficient of friction than the typical GL-5 gear oil to achieve proper and noise (chatter)-free operation.

A limited slip gear oil contains a friction modifier component in addition to gear oil EP components and possesses the required frictional properties. Limited slip gear oils can be used in both limited slip and non-limited slip axles.

Castrol’s limited slip automotive GL-5 gear oil products include the mineral oil-based Castrol Axle Limited Slip 80W-90, the part-synthetic Castrol Axle Limited Slip 75W-90, the full synthetic Castrol Syntrax Limited Slip 75W-90 and the full synthetic Castrol Syntrax Limited Slip 75W-140.

These products offer Castrol customers a range that is capable of servicing most vehicles requiring a limited slip GL-5 gear oil.

Castrol Consumer Relations

Now... if i understood that correctly there is NO need to add friction modifier.

Oil i am thinking of using (Castrol Syntrax Limited Slip LS 75W-140 1L GL-5)

 

[koda2000]

Most here have found that you may still need to add Motorcraft friction modifier to gear oils that already have friction modifier in them. You can try it without, but if your LSD clutches chatter you'll need to add the Motorcraft product. This has been discussed here in the past.

 

[Hacra]

RockAuto had friction modifier bottles for 3.80€ per piece, ordered few, just to be on safe side. Though i am tempted to try without.