A transmission without synchronizers, in which sliding gears or dog clutches engage directly, so the driver must match shaft speeds by double clutching or timing the shift. Heavy trucks, race gearboxes and many tractors use them because they are simple, strong and quick to shift once the skill is learned. A missed shift produces the grinding crash that gives the box its name.
Heard on the job
It's a crash box, so double clutch it, and don't force it into gear or you'll round the dogs off.
Insider tip
Drivers who match revs well enough to shift without the clutch call it floating the gears.
Also heard as
- non-synchro box
- unsynchronized box