1:1 Ford LT 9000 Twin Screw ?

[mavrick0]

Both axles always drive. But if you get into a situation that you loose traction the front axle will put all the power to wheel with less traction and send almost nothing to the rear axle. When you use the interlock it locks both axles together so power is equally transferred to both drives. Without a diff lock you then will get the wheel(s) with the less traction spinning on both axles.