Hydraulic brake for transmission

A hydraulic brake for a transmission, comprising,

• an assist piston, a reaction piston and a main piston disposed on a cylinder so as to be axially arranged sequentially in the named order, such that a first frictional engaging element supported on a rotatable member and a second frictional engaging element supported on a stationary member are brought into pressing contact with each other to couple said rotatable member to said stationary member, said assist piston defining a first oil chamber between a rear end of the assist piston and said cylinder, said assist piston having a first acting portion at a front portion of the assist piston for engaging and urging a rear portion of said main piston, said reaction piston being substantially fixed relative to said cylinder, said assist piston and said main piston being axially slidable relative to said reaction piston, said main piston defining a second oil chamber between a rear portion of the main piston and said reaction piston to communicate with said first oil chamber, said main piston having a second acting portion at a front portion of the main piston for bringing said first and second frictional engaging elements into pressing contact with each other, said first and second acting portions being superposed on each other as viewed axially.