Clutch release clearance adjuster

In a clutch system including a clutch master cylinder (3), a clutch release clearance adjusting mechanism which comprises

• a slave cylinder (1) having an open end, and being connected to said clutch master cylinder (3);
• a piston (59) slidably inserted in slave cylinder (1);
• a release yoke lever (16);
• a push rod (12) connecting said piston (59) with said release yoke lever (16);
• a sleeve (42) coaxial with push rod (12);
• an annular holder plate (36) abutting the open end of slave cylinder (1) and being held inside a boot (37) attached between slave cylinder (1) and push rod (12) and being connected to push rod (12) by way of an adjuster assembly which permits push rod (12) to recede only as far as a predetermined clearance C.sub.2, so as to give a predetermined release clearance C.sub.1 soon after the clutch is fully released, said adjuster assembly consisting essentially of locking means in cooperation with said push rod (12) and said sleeve (42),
• said holder plate (36) being provided with an inner hole (40) in which aforesaid sleeve (42) is slidably journalled as far as clearance C.sub.2 corresponding to release clearance C.sub.1, said sleeve (42) being loaded to project outwardly from cylinder (1) by a spring (46) which is weaker than a return spring (13), push rod (12) being slidably inserted in sleeve (42), and a lock device being installed between sleeve (42) and push rod (12) which device is released only when thrust bwaring (21) is pressed against release levers (24), and
• said push rod (12) being provided with a pipe portion (48) where a head (49) with axial hole (58) is fixed, a lock piece (51) with a tapered portion (52) is inserted in the pipe portion (48), a subsidiary push rod (57) integral with lock piece (51) slidably fits inside hole (58), a compression spring (56) the effective force of which is weaker than the effective force of spring (34) but which is stronger than is return spring (13) being disposed between lock piece (51) and the bottom of pipe portion (48), steel balls (54) are disposed in respective holes (55) facing sleeve (42) and tapered portion (52), and push rod (57) projects from head (49) as far as C.sub.3 against piston (59) when steel balls (54) lock sleeve (42) and push rod (12).