Imp gear shift

The neat little engine was mated to a neat little gearbox.

When the engine was decided upon, the next thought was on the gearbox. It had to be amenable to the output of the lively engine. If the engine was to give its best, revolutions ought to be kept high and full use should be made of the gearbox. The box that had been in the prototype sofar just was not up to the job. It was decided to have one made especially for the Imp, tailored to fit in a fairly cramped compartment.

Rootes hadn't designed a transaxle before, or a gearbox plus differential. November 1960 they hired Adrian West as Senior Transmission Engineer. He had traveled around the European continent on a scholarship studying gearbox design, visiting Renault, Fiat and Simca a.o.

Adrian West set out to tackle the problems. He wanted to set a new standard in gear shifting: speed and lightness would be remarkable !
Also, in 1959 Alec Issigonis had stated that synchromesh for the first gear was impossible, and West would like to prove him wrong.

The design succeeded handsomely. All four gears have really efficient baulk-ring synchromesh, and one can change down to any gear at the maximum speed for that ratio without double declutching or synchronizing the engine speed. Few car magazines failed to sing its praise. It has a very nice, precise shift, as quick and easy as one could wish for. The choice of ratios is outstanding.
The gearbox casing is die-cast from light alloy to save weight.

With all the ratios indirect there is always a bit of transmission whine, even in top gear. The synchromesh ia powerful, but it isn't always easy to select first gear.

"[...] a delightfully rigid lever moving in a very compact positive gate [sexy, isn't it ? ;-)], the transition from one gear to the next becomes very smooth, particularly for quick changes as the revs rise and fall very rapidly with the light flywheel. The ratios come very near to the ideal m.p.h. steps per gear, at the same time keeping bottom gear low enough to allow a contemptuously easy start on a 1 in 3 hill. Reverse gear, protected by an impact spring loading, needs a hefty slap to get the lever in the right plain. "

Final drive is to a transaxle and the standard gearing is such that at 1,000 rpm in the highest gear the Imp does 15mph.
In tests it was shown that maximum speeds of 27,47 and 71 mph correspond to approximately 6,500rpm. The engine could be taken up to 7,000rmp without protest. The maxima recommended by Rootes were conservative. For fourth gear the recommended maximum was at 70mph.