This blog, in addition to the usual maintenance details for classic mini cars, an attempt is made to explain the "whys" and "wherefores" of the various jobs.

Sunday, 18 October 2009

The Automatic-transmission Models

The automatic transmission which is available on the Austin and Morris Minis provides two-pedal, fully-automatic motoring or complete manual control of the gears, at the choice of the driver. It is particularly well suited to the Mini, since it gives four gear ratios instead of the two or three provided by most other types of automatic transmission. A hydraulic torque converter replaces the clutch and ensures a very smooth take-up of the drive from a standstill and when changing gear.

Driving the "automatic" Mini is delightfully simple if the gear lever is moved to the D position, after starting the engine with the lever at N (an automatic cut-out ensures that the starter mechanism can operate only when the selector is at Neutral). With D or Drive engaged, the trans-mission will change up at speeds which depend on the amount of throttle opening, but the maximum engine revs are limited by a governor in the transmission to the equivalent of about 22 m.p.h. in first gear, 34 m.p.h, in second, and 50 m.p.h. in third.

When maximum acceleration is required, a "kick-down" switch which comes into action at the extreme limit of the throttle-pedal travel will engage the next lowest gear, the maximum speed limits for a kick-down change being approximately 17, 28 and 40 m.p.h. in first, second and third gears respectively.

Probably the most attractive feature of the transmission for the keen driver, however, is the fact that downward changes can be made instantly and very smoothly simply by moving the gear lever to the appropriate position. A "zig-zag" between the second and third gear positions acts as a stop when changing from top to third, preventing accidental engage¬ment of second gear, which might over-speed the engine. The main point to remember, in fact, when controlling the gearbox manually, is not to change down at a road speed which is above the safe engine speed for the next lowest gear. The limits are 50 m.p.h. in third gear and 40 m.p.h. in second gear.

The third feature of the transmission is that any gear can be selected and retained—even top gear when starting from rest. The torque con¬verter will take up the drive smoothly and progressively and the car can be allowed to glide along quietly in traffic, without excessive gear changing and high engine revs. Since the kick-down is operative only when the lever is at D, full throttle can be used without causing a downward change when any of the other gear positions has been selected.

It will be seen that both the beginner and the enthusiast are admirably catered for by this transmission and if you are contemplating the purchase of a used model the higher cost of an "automatic" Mini would probably be more than justified.