The assembly seen below the main drive gear on the mainshaft is the planetary gear set. This is the assembly that "splits" the incoming torque from the transmission into the 61%/39% ratio. Here is what the gearset looks like: Look closely and you can see the planetary gears in a carrier on the mainshaft. Next to it on the right is the mating gear housing. Essentially the way this works is: The mainshaft on the left is actually two shafts, one inside another. The outside shaft receives all of the torque from the transmission output.