A commonly asked question by those with vehicles equipped with a limited-slip differentials is, “Do I need to add a limited slip additive (or friction modifier) when changing to AMSOIL Synthetic Gear Oil?”.

Our answer is a qualified “yes”, but please read on.

All AMSOIL Synthetic Gear Lubes for automotive applications have the following recommendation on the label:

AMSOIL SEVERE GEAR™ is compatible with most limited slip differentials. If limited-slip differential chatter occurs, add AMSOIL Slip-Lock™ Friction Modifier Additive.

In many cases, limited-slip differentials perform just fine with only AMSOIL Synthetic Gear Lube and no extra friction modifier added. However, diff chatter can occur in some cases.

Our recommendation: Rather than take a chance, add 2/3’s of a bottle of AMSOIL Slip-Lock™ Friction Modifier Additive or 2/3’s of a bottle of your OEM friction modifier. The additive label may say otherwise, but as the AMSOIL Gear Lube alone is all that is needed in many cases, we find find that 2/3’s of a bottle is quite sufficient.

Limited-slip additive is inexpensive and there is no performance downside to this approach. You will simply eliminate the possibility of any irritating differential chatter.

What Exactly Does Friction Modifier do?

Limited-slip differentials contain clutches that automatically deliver more power to to a wheel that has traction and less to a wheel that is slipping. Friction Modifier additive eliminates noise that can occur when limited-slip mechanisms engage and disengage.

Here is a video produced by Toyota that discusses each type of differential.