سایش سنکرونایزر

The ring that matches a gear's speed to its shaft in the instant before the sleeve slides over — the part that makes a shift silent. Worn, it lets the teeth meet while still turning at different speeds: crunch on the way into gear, resistance the shift fork must force through, and under load a gear that can walk back out of mesh.

In an automated gearbox the module feels what your hand would have felt — shifts on that rail measure slow or incomplete, and the fork position codes tell the story. A synchroniser wears together with the fork that drives it, so the pair are inspected — and budgeted — as one.