Abstract: A mobile vehicle having at least one endless driven member for driving the endless member on a surface capable of supporting a magnetic circuit. The vehicle is equipped with a magnetic system that is housed in a substantially hermetically sealed enclosure and comprises a magnet, a fixed magnetic circuit member, and a movable magnetic circuit member for establishing first and second magnetic circuits. A clutch is provided to selectively connect the movable magnetic circuit member to the motor to move the movable magnetic circuit member between a first position wherein the first magnetic circuit is established such that the endless driven member can magnetically engage the surface and a second position wherein the second magnetic circuit is established such that the endless member does not magnetically engage the surface. The enclosure is pressurized with a pressure medium at a predetermined pressure and temperature and is monitored by sensors within the enclosure.