Originally Posted by 
JDNSW
				
			 
			Free wheel units like this were introduced on cars in the 1930's, mainly because when fitted with one of these you can easily and noiselessly change gears without having synchromesh, as the gearbox stops moving almost as soon as you disengage the clutch. While the general introduction of synchromesh made them somewhat redundant, they continued to be fitted to semiluxury and luxury British cars into the sixties, as they make it easy to drive very smoothly. They were often combined with overdrive to give extra gears.
John