4Matic , BMW with the xDrive , and Volkswagen 's 4motion , for example, can mean either an automatically-engaging "on-demand" system with a Haldex Traction clutch , or a continuously-operating permanent 4WD system with a Torsen (torque-sensing) differential . Engine & solid axle swap Build 02-28-2009,  09:04 AM #7 MiniBrutes View