The reason for inclusion of the differential locker was legislative in nature. LJ80s, SJ410s and early SJ413s had a parking brake which brakes the gears in the transfer case instead of braking the individual rear wheels directly and simultaneously (like in most passenger vehicles). That design has several advantages, as well as an important disadvantage - because of the open rear differential, the hand brake has no effect when the transfer case is in two wheel drive (rear wheel drive) mode and when one of the rear wheels is raised in the air. Therefore, relying on the parking brake itself would be dangerous in some relatively rare situations. German law required that this risk must not exist.