Aisin B400 / B-600

Aisin's B-series six-speed automatics, in light commercial vehicles.

⚑ The number is a TORQUE rating, as it is on Getrag's 420G and Aisin's own 80-40LE — not a model year and not a gear count. A B-600 handles more than a B400 and is a physically larger gearbox.

These are commercial-vehicle units and the duty cycle is the thing that shapes them: heavy loads, frequent stops, long idling, and a service life measured in hours rather than distance. Mileage is a poor guide to condition.

Fluid and its interval decide the outcome. Aisin specifies its own fluid and a shorter interval under load than the base schedule implies, and overheating is the failure mode behind most of what gets reported as a shift fault.

Aisin's TF and TL series are different families for passenger cars, with their own pages here.