Yukon friction modifier / Posi additive. Help keep Positraction chatter down with Yukon's popular friction modifier (Posi additive) for limited slip differentials with composite clutches like the Yukon Dura Grip.. Yukon Limited Slip Friction Modifier is a proprietary Yukon blend that reduces noise and chatter in clutch driven positraction units and limited slip differentials. As clutch packs wear they can develop a chatter, our Modifier enhances the abrasive properties of the clutches to retain stock-like engagement. Formulated for composite clutches, like those found in Yukon Dura Grip LSDs, Yukon Limited Slip Friction Modifier will outperform parts store grade modifiers because they are formulated for OEM paper-style clutches and contain one-fifth the abrasive chemicals.