Portal gear hub with vent bellows

A portal gear box assembly for an off-road vehicle such as an all-terrain vehicle or a utility task vehicle, the assembly comprising:

• a) a sealed portal gear box housing having an interior housing space defined by a rear wall, a front wall, and a side wall,
• wherein the rear wall includes a vehicle axle opening effective to receive the end of an axle of an all-terrain vehicle or a utility task vehicle, and
• wherein the front wall includes an output shaft opening effective to receive the end of an output shaft effective to power a vehicle wheel;
• b) a set of gears housed in the housing and effective for linking an axle received in the vehicle axle opening to an output shaft received in the output shaft opening;
• c) an output shaft operably connectable via said linking mechanism to an axle received in the vehicle axle receptacle, and effective to rotate upon rotation of the stock axle;
• and
• d) an expandable space in fluid communication with the interior housing space and adapted to allow pressurized fluid contained in the interior housing space to flow into the expandable space, thus expanding the volume of the expandable space and reducing the pressure within the interior housing space;
• wherein the expandable space comprises a bellows whose volume can be changed by expansion or contraction of a fluid contained therein;
• wherein the expandable space is mounted externally to the portal gear box housing;
• wherein the expandable space is connected to the portal gear box housing by a conduit effective for allowing fluid to pass between the portal gear box housing and the expandable space;
• and
• wherein the externally mounted bellows is positioned to expand vertically with respect to the housing.