Engine transplants - gearbox information
A subject worthy of an entire book to explain the whys and wherefores, and also causes much consternation on the part of the transplanter.
Terminology -
BBU - Big Bore Unit
SBU - Small Bore Unit
FD - Final Drive (diff ratio)
A subject worthy of an entire book to explain the whys and wherefores, and also causes much consternation on the part of the transplanter. Much confusion’s spread over which gearbox has the best ratios, is best to use, and with which FD. For a detailed account on this and covering all gearboxes fitted as standard to the Mini, see the relevant separate articles 'Gearbox - Standard production gearbox types'.
Fortunately, when selecting a complete engine and gearbox unit from a Metro, the gearbox will pretty much suit the engine and be easily transplantable whole into the Mini. It shares exactly the same rod-change linkage as the Mini. Difficulties only arise when fitting a rod-change gearbox into a pre-1973 Mini that has the old remote-type gear-change mechanism, but not insurmountable. It's dealt with in the 'Ancillaries' appendage to this series.