Just a quick addition
			 
			 
			
		
		
		
			
			These trucks did come with a two-speed rear axle, but I think the two-speed axles were limited to those variants that had dual rear wheels. 
 
Since the truck in the photo has single rear wheels I'd expect it to have a single speed rear axle, plus things like a transmission-mounted tyre pump. 
 
Gordon
		 
		
		
		
		
		
		
			
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				Gordon,   in Scotland
			 
		
		
		
		
		
	
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