Abstract: A coaxial adjustable hydraulic clutch actuator of the invention for use with an automotive transmission and clutch, as in a racing vehicle for coupling power from the engine to the transmission. The transmission has a power input shaft and the clutch has actuating elements, the engine and transmission being joined by a bell housing. The actuator includes a base housing configured for retaining a bearing of the input shaft. A sleeve extends forwardly from the base housing coaxial with the input shaft. A piston is fitted coaxially within the sleeve and is received within an annular hydraulic fluid chamber to which hydraulic fluid is supplied under pressure from exteriorly of the bell housing. A clutch throw-out bearing is carried coaxially by the piston for being driven into throw-out engagement with the actuating elements of the clutch by movement of the piston in response to the hydraulic fluid pressure for clutch actuating operation.