the following description of the preferred embodiment ( s ) is merely exemplary in nature and is in no way intended to limit the invention , its application , or uses . the drive assembly in accordance with the invention has a shear pin coupling 1 which defines a longitudinal axis 2 which also constitutes the axis of rotation of the shear pin coupling 1 . the shear pin coupling 1 includes a coupling hub 3 with a bore 4 centred on the longitudinal axis 2 . the bone includes teeth which are shown in fig3 . a transverse bore 5 intersects the bore 4 . a tensioning element 6 is threaded into the transverse bore 5 . the tensioning element 6 may fix the coupling hub 3 on the shaft of a transfer box . the shaft includes corresponding outer teeth . the coupling hub 3 has a seat face 7 . a first projection 8 radially projects from the seat face 7 and has a flange - like design . the seat face 7 ends in a first running groove 9 , which constitutes a bearing seat . the first running groove 9 is an annular groove centred on the longitudinal axis 2 . a first receiving bore 10 in the coupling hub 3 is radially offset relative to the longitudinal axis 2 . the first receiving bore 10 extends parallel to the longitudinal axis and extends through the first projection 8 . the first projection 8 forms a first contact face 11 that extends towards the first running groove 9 . the shear pin coupling 1 includes a coupling sleeve 12 which , in the present embodiment , embraces the joint yoke 13 with its two yoke arms . the joint yoke 13 constitutes part of a universal joint which , in turn , forms part of a driveshaft . the coupling sleeve 12 has a bore 15 . a second running groove 14 , in the form of an annular groove , is arranged around the longitudinal axis 2 . the coupling sleeve 12 , by means of its bore 15 , extends over the portion of the coupling sleeve 3 that contains the seat face 7 . the first running groove 9 is positioned opposite the second running groove 14 . the running grooves 9 and 14 together accommodate bearing balls 16 . thus , the coupling sleeve 12 and the coupling hub 3 are rotatable relative to one another . the coupling sleeve 12 includes a second projection 17 . the second projection 17 includes a second receiving bore 19 . the arrangement of the second receiving bore 19 corresponds to the arrangement of the first receiving bore 10 relative to the longitudinal axis 2 in the first projection 8 . the second receiving bore 19 extends parallel relative to the longitudinal axis 2 . the second projection 17 and the coupling sleeve 12 form a second contact face 18 which extends towards the first projection 8 of the coupling hub 3 . the shear pin coupling 1 includes a ratchet gear 20 . the ratchet gear includes a bearing bore 21 centered on the longitudinal axis 2 . additionally , the ratchet gear 20 has a first end face 22 and a second end face 23 . the ratchet gear 20 , via the bearing bore 21 , is rotatably supported on the seat face 7 of the coupling hub 3 . in the direction of the longitudinal axis 2 , the ratchet gear 20 is held by its first end face 22 against the second contact face 18 and by its second end face 23 against the first contact face 11 of the coupling hub 3 . the ratchet gear 20 , on its circumference , includes plurality of projecting cams with holding faces 25 . the holding faces 25 extend radially relative to the longitudinal axis 2 . a third receiving bore 24 is arranged at a radial distance from the longitudinal axis 2 . the receiving bore 24 extends parallel relative to the longitudinal axis 2 . the longitudinal axis of the receiving bore 24 is collinear to the first receiving bore 10 and the second receiving bore 19 . a shear pin , in the form of a head screw 26 , is guided through the receiving bores 10 , 19 , 24 . additionally , the shear pin , by a nut 27 , tensions the coupling hub 3 , the ratchet gear 2 and the coupling sleeve 12 . the head screw 26 is preferably received in a play - free way in the receiving bores 10 , 19 , 24 . as a result , the coupling hub 3 , the coupling sleeve 12 and the ratchet gear 20 are connected to one another in a rotationally fast way . thus , when rotatingly driven by the joint yoke 13 , the hub 3 , sleeve 12 and gear 20 have to rotate together around the longitudinal axis 2 . the drive assembly in accordance with the invention , includes a locking device 28 in addition to comprising the above - described shear pin coupling 1 . the locking device 28 is best seen in fig2 . the locking device 28 includes a locking element in the form of a locking ratchet 29 . the locking ratchet 29 is arranged at a stationary bearing and is pivotable around the pivot axis 30 . the locking ratchet 29 is held by a spring 32 in an inactive position . the locking face 31 is disengaged from the holding faces 25 of the ratchet gear 20 . the ratchet gear 20 is pivoted around the pivot axis 30 by an actuating mechanism ( not shown ). the locking face 31 moves into the path of movement of the holding face 25 of the rotating ratchet gear 20 when the gear 20 is driven in the rotational direction n . thus , the ratchet gear 20 is abruptly stopped . as a result , the head screw 26 shears at least one of the two shear faces formed in the region of contact between the ratchet gear 20 and the first projection 8 or the second projection 17 . thus , the transmission of torque is interrupted between the coupling hub 3 and the coupling sleeve 12 and , respectively , between the coupling sleeve 12 and the coupling hub 3 . fig4 shows the drive assembly associated with a transfer box of a drive system for an agricultural implement . the transfer box has been given the reference number 33 . it is attached to a machine frame ( not shown ), for example . the drive is effected via the driveshaft 34 and the shear pin coupling 1 . the torque introduced into the transfer box 33 is distributed to the two output shafts 36 , 38 . in fig4 the shear pin coupling 1 is disconnected from the driveshaft 34 in order not to obstruct the view of the shear pin coupling 1 and , in particular , of the locking device 28 . the transfer box 33 is associated with a bracket 37 which pivotably supports the locking ratchet 29 of the locking device 28 . fig4 also shows how the locking ratchet 29 , by its locking face 31 , is associated with the holding face 25 of the ratchet gear 20 . the head screw 26 acting as the shear pin can also be seen . the actuating device 38 includes a setting element which directly acts on the locking ratchet 29 ends at the bracket 37 . the setting element itself can be activated by a bowden cable , an actuating lever or a release cord . alternatively , the setting element may be an electrically , pneumatically or hydraulically operated power drive . the power drive is connected , by lines , to an actuating switch , an actuating valve or a sensor to release the actuating function . the description of the invention is merely exemplary in nature and , thus , variations that do not depart from the gist of the invention are intended to be within the scope of the invention . such variations are not to be regarded as a departure from the spirit and scope of the invention .