Getrag 420G / 560G

Getrag's big rear-drive six-speed manuals — the 420G behind BMW's V8s and the 560G behind the V12s.

⚑ The number is a TORQUE rating, not a model year or a size in the usual sense: 420 and 560 are newton-metres. That is why a 560G sits behind a twelve-cylinder engine and a 420G behind an eight — and why fitting the smaller unit to a modified car is a well-known way to break it.

They are heavy, long and cast in iron, built for torque rather than for shift feel. The characteristic complaint is weight at the lever and a deliberate action, which is the design rather than a fault.

Fluid specification is the item that decides one's life. Getrag specified its own oil, the interval is longer than most owners assume, and a general gear oil produces exactly the notchy cold shift that gets diagnosed as synchroniser wear.

Parts are scarce and specialist. These were fitted in small numbers to large cars, and a rebuild is a specialist job rather than a dealer one.