I have an MTD Gold 2 stage 600 series snow thrower. It has been working fine but now won't move. Engine is fine. Won't even roll. I have it on it's end and the drive plate and belt look fine. I've slid the large gear assembly that consists of a big and small gear to the left. Everything spins. I slide the small gear on the hex shaft to the left to meet the big gear and everything spins. I slide the big gear assembly back to the right, leaving the small gear on the hex shaft left, and engage the small gear on the gear assembly to the large gear on the hex shaft and everything spins. Re-engage the small gear on the hex shaft and nothing moves.

Summary: When the two gear(small and large) assembly that is left most on the axle is engage with both small and large gear on the hex shaft, nothing moves.

When one of the two gears on that assembly is engaged with it's respective gear on the hex shaft everything spins. Together nothing.