155.172

A synchronizer is a gearbox part that matches the speed of two rotating parts so a gear can be selected smoothly.

As a gear is selected, the synchronizer's friction cone brings the gear and shaft to the same speed before they lock, preventing the grinding and wear of clashing gears.

Synchronizers sit inside the manual gearbox, one for the gears they serve. The correct synchronizer matches the specific gearbox and gear position.