Anyone know what is the purpose to the sub gear on the 3rd gear? It seems to spins freely. It is part number MD730051

I was told once it is for noise suppression but PM the tranny expert pro Twicks69 (tmzperformance.com) to be sure and report back. I'd like to hear what he has to say too.

Bump.
I've recently disassembled a trans that did not have the subgear installed. I'm curious what it does also. Given it's on 3rd gear in an AWD I'm guessing per above statements that is has something to do with noise since 3rd is always affected heavily as it's the main drive gear for the entire unit. The OP posted a part number which I have discovered is year specific which makes sense as I'm aware of the changes from year to year on 3rd gear. This also happens to be an evo3 3rd gear so that will complicate things if I want to add this sub gear as I'm sure the parts are likely hard to get. This unit has all evo3 gears and 2nd is ripped off the input shaft so that will be a challenge to find a new input shaft.

Noise suppression. I take them out usually, they just seem to grab shrapnel and pull it into unharmed gears

I've also never questioned the need for snap rings to hold the bearings when they're pressed on but this particular unit also had no snap rings on any bearing retainer.