a socket 140 having a bore 142 into which a spherical ball 144 located at the end of the shift lever is fitted shift rail 134 carries several shift forks 146 148 and other forks not shown in fig1 but illustrated in fig4 each shift fork engages a synchronizer sleeve 58 70 84 112 thereby transmitting movement of the shift lever through socket 140 the shift fork associated with the selected ratio and the appropriate synchronizer sleeve rail 134 carries a radially directed finger 150 and an interlock sleeve 152 which is held by bolt 154 against displacement along the axis of rail 134 each shift fork includes an arm that extends to the vicinity of bolt 154 or bolt 192 and provides a slot aligned with the radial path of the shift fingers 150 or 188 as it rotates about the axis of shift rail 134 due to displacement of the shift selector 122 along the neutral horizontal plane of the diagram of fig2 when a selector finger rotates into engagement with a slot on a shift fork corresponding to the position of the selected gear ratio the shift fork is subsequently moved axially causing the associated synchronizer sleeve to engage and to connect the selected gear pinion sleeve or carrier with the shaft on which the hub of the corresponding synchronizer is supported the mechanism that transmits movement of the gear shift lever to the components of the transmission that engage and release the selected gear ratios is shown in greater detail in fig4 in addition to the components of the shift mechanism described with reference to fig1 above the mechanism includes a lower shift rail 170 which is journalled at the left hand side on casing 10 and at the right hand side.