The BN 1 model, inherited its transmission from the A70/A90 models. This needs some explanation. These Austins had four-speed gearboxes with a steering column change. The Austin-Healey had a three-speed gearbox with a floor change. What happened was that although the original first gear was left intact inside the Austin-Healey gearbox, the first gear selector was omitted and so the original second gear became first etc.

Since this gearbox had been designed for a steering column change, it had side-mounted selectors, and therefore the Austin-Healey ended up with a gear lever mounted on the left-hand side of the transmission tunnel. The gearshift pattern was unusual. First was central and back; second was to the left and forward; third was back from second; and reverse was to the right and back.

The reason for abolishing the original first gear was that this was far too low for the much lighter and more powerful sports car. To compensate at the other end of the scale, the Healey was fitted with a Laycock de Normanville overdrive (bolted to the back of the gearbox) as standard. This operated on second and third speeds and was controlled by a switch on the facia. The net result was that the Healey driver had five speeds to play around with.

The clutch was a mechanically operated Borg & Beck single dry-plate type of 9in diameter. On the BN1, the clutch housing and gearbox were in one piece, and were mostly left in unpainted aluminium. One side effect of using a three-speed version of a four-speed box was that all forward gears had synchromesh.

The most important change to the BN1 transmission came early in the production run, when the type of overdrive was changed from WN1260 (with a 28.6 per cent reduction). This happened at chassis number 140205 as early as August 1953, which in effect means that only a handful of cars had the early type overdrive. A close-ratio overdrive (22 per cent reduction) was optional.

Allowing for the two different overdrive reduction ratios, and also for the subsequent change in final drive ratio when the hypoid axle was introduced, we get the following table of internal and overall gear ratios:

These tables do not take into account the alternative rear axle ratio of 3.66 to 1 quoted for the spiral bevel axle, but this would obviously affect the overall ratios quoted above, as would the optional close-ratio 22 per cent reduction overdrive.

The gearlever itself was chrome-plated and had a round black knob, with the pattern engraved in white. The lever had a moulded rubber gaiter at its foot, usually with a Vynide area inset in the carpet surrounding it. Because it was offset to the left, the gearlever on left-hand drive cars was much shorter than on right-hand drive cars.

The biggest single modification on the BN2 model from chassis number 228047 in August 1955, was the introduction of a new four-speed gearbox, with syn-chromesh on the upper three ratios. As the dual overdrive - now working on third and fourth speeds - was still fitted, there were now in effect six gears. The new gearbox was that of the recently-introduced Austin A90 Six Westminster model, and as it was still primarily designed for steering column change, the Austin-Healey gearlever remained off-centre. At least it now had a normal shift pattern - First in the centre and forward, second behind, third to the right and forward, fourth behind, and reverse on a dog leg to the left and back. The ratios were now as in the table on the right.

The overdrive itself was also modified on the BN2 model. Most importantly, there was now only one overdrive relay instead of the two relays found on the BN1, and the wiring was simplified. The overdrive reduction ratio was now 28 per cent. The type of overdrive was WN1308.

Originally, the BN2 cars used the same gearlever on right-hand and left-hand drive cars, but from chassis number 228487 the gearlever was modified, with two alternative types of gearlever being quoted for either right-hand or left-hand drive cars. The shape of the transmission tunnel was altered on the BN2 model, the tunnel being squarer in section, and the rubber gaiter for the gearlever was sunk below the level of the carpet. The edge of the carpet around the gearlever hole was bound in Vynide. Where the BN1 had a Vynide covered access panel for the gearbox oil filler on the right-hand side of the tunnel, the BN2 had a rubber plug for the compined dipstick and oil filler under the carpet at the rear of the gearbox cover. Finally, it must be mentioned that on the BN2 there was a separate aluminium clutch housing, and both this and the cast iron gearbox were now finished in engine paint colour.

The propshaft was of the open type, made by Hardy Spicer, with universal joints front nd rear and always painted black. Originally the propshaft was 21 1/8in long, but with the change in overdrive at chassis 140205 it was shortened to 20 3/4in. The bolts holding the propshaft coupling flange to the overdrive were changed at chassis 155284. With the coming of the hypoid rear axle at chassis 221536, the propshaft was further shortened to 20in.