Abstract: A PTO clutch assembly includes coaxial primary and secondary clutches and in use is initially externally actuated but primarily internally-actuating so as to require relatively low manual or other external actuating forces to engage the clutch assembly--the major portion of the actuating forces being imposed internally by the engine flywheel or the like after imposition of the external forces. The resulting clutch assembly, utilizing the engine flywheel for the major portion of engagement forces, requires only a fraction of the external actuating forces required by conventional over-center clutch assemblies of comparable capacity. The clutch assembly is also partially self-adjusting, with wear of the primary clutch disc stack being compensated through increased axial movement of the actuator for the primary clutch.