Patent ID: 7013643

Claim:
A master cylinder comprising a cylinder body having a central axis, and front and rear ends with respect to the direction of said central axis, said cylinder body having an opening at said rear end, a primary piston slidably inserted in said cylinder body through said opening, thereby defining a first pressure chamber in said cylinder body, said first pressure chamber being filled with brake fluid which can be pressurized by said primary piston, said primary piston being directly in slide contact with and guided by said cylinder body, and a primary cup for said primary piston and a secondary cup both provided between a radially inner surface of said cylinder body and said primary piston, said secondary cup being located rearwardly of said primary cup to shut off communication between the interior of said cylinder body and outer air, said primary cup sealing a gap between said cylinder body and said primary piston, said cylinder body being provided with first, second and third piston guide portions on the radially inner surface thereof, said first piston guide portion being disposed between said primary cup and said secondary cup, said second piston guide portion being disposed between said primary cup and said first piston guide portion, said third piston guide portion being disposed forwardly of said primary cup, each of said first, second and third piston guide portions having a radially inner surface radially opposing said primary piston and formed with grooves extending parallel to said central axis of said cylinder body.