In 1965 the world's smallest automatic gearbox arrived, specially developed by Automotive Products. All parts were housed in the sump and uniquely lubricated by circulating the engine oil. Announced in 1965 but because of many problems only became available in quantity from 1967 making Mk1 versions very rare. Early testing revealed that oil surge in the sump under cornering could cause oil starvation of the torque converter and sky-high engine revs. To compensate for this failing the oil pump was moved to the centre of the sump and oil capacity was increased.
Final assembly problems also arose and manufacture of the gearboxes was transferred to clinically clean, dust free rooms to ensure a dependable assembly of the unit with its numerous hydraulic valves.
The design itself put all known hydraulic boxes in the shade and to make the most of the engine's meagre output, gave four speeds as against the three of other automatics current at the time.
A mechanical control ensured gear selection according to load when in automatic mode, and there was also a kick-down working directly off the throttle pedal. To compensate for the usual auto power losses on an 850cc, the compression ratio was increased to 9:1 and a larger SU carburettor with inlet manifold was fitted. (I can remember searching for the auto Mini's in scrapyards in the 1970's to aquire these parts for upgrading our 850cc manual cars!)
Useful AP Automatic Technical Information:
http://members.tripod.com/austin_america/id72.html
Mini-1100 AP Automatic Transmission:
http://www.austinmemories.com/styled-105/index.html
Automatic Mini Register:
http://autominiregister.proboards.com/
Great BMC Pathe film on factory build of the Mini/1100/1300 Automatic Gearbox (sadly no audio/sound)
Automatic Transmission And Power Units (1967)
https://www.youtube.com/watch?v=ieraaVfUs4Q
