angularly spaced jaws 53 fig3 and 5 which fit tightly but slidably into three angularly spaced notches 54 formed in the upper side of the output member 27 the jaws and the notches function as a spline in that they couple the secondary shoe 50 and the output member 27 for rotation in unison but permit the secondary shoe to slide axially relative to the output member there is little if any circumferential clearance between the jaws and the notches and thus for all practical purposes the secondary shoe 50 is not capable of rotating relative to the output member 27 the jaws 50 also are received loosely within three notches 55 fig5 formed in the disc 34 of the primary shoe 32 and serve as a slidable pilot for the primary shoe there is however circumferential clearance between the jaws and the notches 55 in the primary shoe and thus the primary shoe is capable of moving angularly through a limited distance relative to the secondary shoe 50 and the output member 27 in carrying out the invention means are provided between the output member 27 and the secondary shoe 50 for shifting the secondary shoe axially into engagement with the input member 15 in response to the primary shoe initially being turned by the input member such means acting without causing the clutch 10 to self energize or self servo herein these means comprise three angularly spaced balls 60 which are captivated between lower races 61 fig3 to 5 formed in the upper side of the output member 27 and upper races 62 fig5 formed in the lower side of the plate 51 of the secondary shoe 50 the.