Never worked on one, but from looking at this photo I found on the web,
It looks like the central gearbox has two bolts attaching the gearbox to the central support that should come out, then the bolts holding the bearings on either end need to be removed. At this point you may be able to flex the auger enough to swap out the bearings, but you may need to look for whatever provision there is for holding the driveshaft to the gearbox so you can pull the entire auger assembly off.
From the sounds of it, you're right at the point I described. Look for a set screw on either end of the driveshaft that runs the secondary. If, after a careful examination, nothing seems to hold the central driveshaft onto the gearbox but friction (an unseen force known to mechanics as "magic"), use a rubber mallet on the gearbox and attempt to pull the gearbox off of the driveshaft.
I'm thinking you're missing a set screw that locks in a key on the driveshaft running the secondary fan.
If you see nothing, stop and think about two things:
1) How does power flow to the auger, and,
2) How did this thing run down an assembly line and get put together.
Power flow and thinking about how the blower was assembled should help you think about how it comes apart as smaller assemblies.
If you're still stuck after reading all this, then take photos of the shaft going into the gearbox and good photos trying to show the various components of the driveline and post them. One of us will likely be able to puzzle it out and advise you.
