towards the axis of the clutch it is with the face of the rim 22 which is turned towards the base 12 of the cover 2 that the diaphragm 3 cooperates in the storage position of the mechanism as shown in fig2 by limiting the travel of the diaphragm 3 in storage that of the thrust plate 1 is limited advantageously the thrust plate 1 has opposite the base 12 of the cover 2 radial undercuts 31 in which the radial returns 22 of the lugs 20 can extend it will also be appreciated that by virtue of the invention there has been produced in the context of a mechanism of the pulled type a subassembly comprising the cover 2 and diaphragm 3 which facilitates manipulation as well as the operations of manufacturing the mechanism in addition by virtue of the stop means 20 the diaphragm 3 is centred with respect to the cover which avoids having to provided special centring means for the diaphragm 3 such as for example axial pins located in the thrust plate 1 as has been done up until now according to the variant in fig3 the stop means 20 consist of small columns having a cylindrical body 23 passing through holes 19 in the diaphragm 3 a cylindrical tail 24 with a smaller diameter than that of the body 23 crimped to the base 12 of the cover 2 and a head 25 semicylindrical in shape and with a diameter greater than that of the body 23 on this head 25 on the side which faces the base 12 of the cover 2 there is defined a semicircular stop line 26 for the diaphragm 3 slightly curved in shape fig5 and 6 show.