Synchroniser

Brings two shafts to the same speed before a gear engages, using a friction cone that spins the slower one up as the collar slides across. It is what makes a manual gearbox shift silently, and it is a wearing part — as the cone wears it takes longer to match speeds. A human driver absorbs that without noticing, holding pressure until the gear goes in. An automated gearbox works to a fixed force and a timeout instead, so it records a shift that failed to complete: which is why worn synchronisers announce themselves as electronic control errors on an automated manual, and as a notchy change or a crunch on a conventional one.

Also known as: synchro, synchro ring, synchromesh, baulk ring, blocker ring, synchronizer

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