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Five speed gearbox

The Duetto’s five-speed transmission was carried over with a few changes. The drive-shaft support design changed for the 1750, swapping the rubber mount and steel insert for a new type. The final drive ratio was significantly higher than before, thanks to an increased number of teeth on the pinion and crown wheel (10 on the pinion and 43 on the crown wheel, as opposed to 9 and 41). This equated to a final drive ratio of 4.300:1, with the effect that, although the gear ratios were stacked the same as before, cruising speeds rose. For example, at 1000rpm in top gear, the new 1750 would be traveling at 21.9mph

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NB. 10/41 for 4.1:1 ? All the Alfas & AR68 quote this, while Motor quoted 4.3:1 (I think) BUT its figures (as below) correspond to 4.1:1 figures!

Road speed at 1000rpm in forward gears was as follows:

5^th 21.9mph
4^th 17.3mph
3^rd 12.8mph
2^nd 8.7mph
1^st 5.3mph

Source: Motor magazine, May 24, 1969

The gear ratios were retained as before (BUT Rev = 3.09? instead of 3.01? – I don’t think so), although alternative gear ratios were manufactured by Alfa Romeo, being interchangeable in pairs. Optionally 1^st gear could have 35 teeth, 2^nd gear 30 teeth, 3^rd gear 26 teeth and 5^th gear 21 teeth. There was also an optional 32-tooth lay-shaft gear for 5^th and reverse.

Another significant change was a switch from mechanical to hydraulic clutch actuation. The clutch master and slave cylinders were by Bonaldi or Ate. A ZF manufactured limited slip differential with a 25 per cent lock was offered as an optional extra, and certainly helped with traction, particularly in wet conditions.

The rims were 5.5J x 14, offset 45mm made by CMR "Costruzioni Meccaniche Rho"  actually the famous Borrani wheel manufacturer and CMR are interlinked, the same company so to speak. 

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