Hydraulic clutch release mechanism

In an hydraulic release mechanism for a vehicle clutch in combination with a power transmission unit, said release mechanism comprising a push-rod axially slidable within an input shaft of said transmission unit and having one end engaged with a release member of said clutch and the other end extended outwardly from said housing assembly of said transmission unit and an hydraulic cylinder attached to said housing assembly to urge said push-rod toward said release member, causing disengagement of said clutch;

• the improvement wherein a seal member is adapted to said housing assembly for surrounding the outwardly extended portion of said push-rod in a fluid tight manner, and said hydraulic cylinder includes a cylinder housing provided at its closed end with a port for connection to a source of hydraulic pressure and being detachably secured at its open end to said housing assembly to contain the outwardly extended end of said push-rod therein;
• a piston axially slidable within said cylinder housing and engaged with the outwardly extended end of said push-rod, said piston being provided at its outer periphery with an annular seal member to subdivide the interior of said cylinder housing into a pneumatic chamber and an hydraulic chamber in open communication with said port;
• and a communication passage provided between the open end of said cylinder housing and the outer wall surface of said transmission housing assembly to vent said pneumatic chamber to the atmospheric air, said communication passage having the upper end opening into the bottom portion of said pneumatic chamber and the lower end opening adjacent to an embossed portion of said housing assembly.