Ford M5OD / M5OD-R1

Ford's rear-drive five-speed manual — in the Ranger, Explorer, Sport Trac, Aerostar and F-150, and in the Mazda BT-50.

It is a Mazda design, which is why a BT-50 and a Ranger share a gearbox and why the Mazda parts catalogue is a legitimate source for a Ford truck.

The letters are a size, not a variant. The M5OD-R1 is the light unit behind the four-cylinder and V6 Rangers and Explorers; the R2 is the heavier one behind the F-150's V8. They are not interchangeable and a parts listing that says only M5OD covers both.

Its recurring failure is the fifth-gear synchro and the bearing behind it, presenting as a grind into fifth alone or a whine that appears only in fifth. Fifth sits at the back of the case on its own, which is why it wears first and why the repair does not require disturbing the rest.

It takes a specific fluid and this is where most of the avoidable damage comes from. The R1 wants a Motorcraft manual-transmission fluid rather than a gear oil, and a conventional 80W-90 makes it notchy cold and grinds into second — the same mistake as on the NV3500 and the AX-15, in a third marque.