Aisin AE6

Aisin's six-speed manual for one-tonne pickups — in the Isuzu D-Max and MU-X, and the Mazda BT-50 that shares their platform.

A Mazda pickup with an Isuzu platform and an Aisin gearbox is exactly the sort of thing no single marque's literature explains, and it is why establishing the gearbox rather than the badge is worth doing first.

It is a working gearbox and its faults are the faults of load. The clutch goes first in almost every case — a bite point that has climbed, or a slip in the tall gears under load — and on a vehicle used for towing that is a wear item rather than a fault.

Where the gearbox itself wears it is the second-gear synchro and the shift forks, presenting as a crunch into second on a fast cold change, or as a gear that will not stay engaged. The second of those is a fork rather than general wear and is repairable on its own.

A crunch into every gear is the clutch not releasing, which on these is usually the hydraulics rather than the plate.