Abstract: A gear shift device for gear boxes for vehicles, comprising at least one pair of mutually connected, double-acting hydraulic cylinders (1,2), where the pair consists of a master cylinder (1) and a slave cylinder (21). The master cylinder can be operated via a gear lever and the slave cylinder moves a mechanism which is connected to gear selector carriers in the gearbox. According to the invention each end section of the master cylinder's (1) piston (4) has an outer (54 or 55) and an inner (56 or 57) piston sealing ring which are arranged at intervals, calculated in the piston's longitudinal direction, and in these end sections there is provided a drilling (52 or 53) whose first end leads into the piston surface between the respective end sections outer and inner sealing rings (54, 56 and 55, 57 respectively), and whose second ends leads into the adjacent end face of the piston (4).

Abstract: A clutch-servo for vehicles which constitutes a working device arranged for fluid connection with a master cylinder to be operated by the vehicle's driver. The servo comprises a working cylinder unit (50) with a piston (5) arranged in a working cylinder (1), which piston is connected to the clutch's engaging mechanism, and a control valve unit (60) for the working cylinder unit (50), with a valve body (21) arranged in the valve housing (44). The master cylinder has a fluid connection with the working cylinder unit (50) and the control valve unit (60), so that the fluid in the master cylinder simultaneously exerts a force on the piston (5) and the valve body (21), in order to try to release the clutch and to move the valve body (21) in order to connect the working cylinder unit (50) to a servo pressure fluid source when the driver operates the master cylinder. According to the invention the valve unit is constituted by a slide valve.