50 IV - CLUTCH LOCK : 1. ed Purpose : This unit is present to stop the clutch re-engaging during changes to and from Ist and 2nd gears, if one or other of the gears in not fully engaged. This safety measure is mainly justified on the re-engagement in Ist gear; due to the absence of a 1st gear synchro delay piston in the hydraulic selector, the latter could allow re-engagement before the synchro and locking dogs have had time to operate.