Abstract: A synchronizer mechanism for synchronizing the rotation of gears between a power input shaft and a power output shaft in a manual transmission includes a hub and a synchronizer sleeve disposed about the hub and moveable relative thereto into and out of engagement with adjacent gears to synchronize the rotation of the adjacent gears with the rotation of the power input shaft. An indexing mechanism is employed for indexing the synchronizer sleeve into and out of engagement with adjacent gears. The indexing mechanism includes a retaining mechanism and a detent portion having a pair of gear engagement positions and a neutral position disposed therebetween. The retaining mechanism is receivable in the gear engagement positions and the neutral position to positively hold the synchronizer sleeve in these positions thereby preventing errant movement of the sleeve as it is moved into and out of engagement with adjacent gears.