Dismantling 3 Wheeler Gearbox: Idler in Differential Case

[monty37]

i recently dismantled a 3 speed (tuk tuk) gearbox.But unlike usual 4 wheelers,i found the
idler in the differential case.usually for reverse ,idler is also present in the gearbox .
When i asked i was told that in 3 wheelers when the reverse gear is applied,the differential as a whole rotates in the opposite direction ,so reverse can be applied in any gear(1or 2 or 3).
But i have always read that reverse gear is a single gear having its own gear ratio.

 

[monty37]

I meant a 3 wheeler gearbox having 4 gears (forward) and one reverse

 

[tvavanasd]

Seems a little dangerous to keep all 4 gears available in reverse.

Two thoughts:
The gearbox (or gearbox design) could have evolved from that of a motorcycle (without reverse). It may just be simpler that way.

Putting the reverse gear at the differential keeps drive components between gearbox and differential rotating in only one direction. Not sure if this offers an advantage.

 

[monty37]

but nobody wants 4 gears in reverse so where is the advantage in keeping the idler with
the differential.Is it because it is a rear engine rear drive?