Redline Friction Modifier & Break-In Additive - 4 oz. Redline Friction Modifier is highly recommended for Limited Slip Differentials. Compatible with petroluem or synthetic gear oils, this product will significantly reduce the friction break-in of differentials, reducing break-in temps for as much as 50 degrees F. Limited slip or positraction units will often chatter without use of this product or a gear oil with a similar modifier, so add only enough to eliminate the chatter and avoid making the plates or clutches too slippery.