The automatic transmission fitted as an optinal extra to Mini models incorporates a three element fluid torque converter with a maximum conversion ratio of 2:1 coupled to a bevel gear train assembly.
The final drive is transmitted from a drivegear to a conventional type differential unit, which in turn transmits engine torque through two flange type coupling driveshafts, employing constant velocity joints, to the roadwheels.
The complete geartrain assembly, including the reduction gears and differential units, runs parallel to, and below, the crankshaft and is housed in the transmission casing which also serves as the engine sump.
The system is controlled by a selector lever within a gated quadrant marked with seven positions and mounted centrally on the floor of the car. The reverse, neutral, and drive positions are for normal automatic driving, with the first, second, third, and fourth positions used for manual operation or override as required. This allows the system to be used as a fully automatic four-speed transmission, from rest to maximum speed with the gears changing automatically according to throttle position and load. If a lower gear is required to obtain greater acceleration, an instant full throttle position ie, kickdown on the accelerator, immediately produces the change.
Complete manual control of all four forward gears by use of the selector lever provides rapid changes. However, it is very important that downward changes are effected at the correct road speeds otherwise serious damage may result to the automatic transmission unit. The second, third and top gears provide engine braking whether driving in automatic or manual conditions. In first gear a freewheel condition exists when decelerating. Manual selection to third or second gear gives engine braking and also allows the driver to stay in a particular low gear to suit road conditions or when descending steep hills.
Due to the complexity of the automatic transmission unit, if performance is not up to standard, or overhaul is necessary, it is imperative that this be left to the local main agents who will have the special equipment for fault diagnosis and rectification.
The content of the following Sections is therefore confined to supplying general information and any service information and instruction that can be used by the owner.
Automatic transmission - removal and refitting
The automatic transmission is removed from the car together with the engine and differential assembly as described in Chapter 1.
It will then be necessary to separate the gearbox from the engine; again, full information will be found in Chapter 1.