Komatsu PC88MR-10 Shop Manual page 207

Operation when travel lever is in neutral
When the travel lever is returned to NEUTRAL, the pressurized oil from the control valve is blocked.
The pressurized oil in chamber (A) of brake piston (2) is drained into the case.
When the pressure in chamber (A) decreases below the reaction force of spring (3), brake piston (2) is
pushed back to the right.
Brake piston (2) presses plate (4) and disc (5) together, and the parking brake operates.
PC88MR-10
10 Structure and function
Travel motor
10-129