Worked for weeks on my 9N to get it running and finally got it to work.  While letting it idle and get the engine warmed up so I could flush the cooling system, I hear a "thunk" in the tranny area and the engine immediately dies.  I got back on board and depressed the clutch while cranking and got it back running, but as soon as I let off the clutch, the engine dies.  I restarted it multiple times with the same result.  I moved the gear shifter around and tried to see if the tractor would move when I let out the clutch, but no matter what gear I'm in, the tractor doesn't budge and inch - it just dies unless the clutch is engaged.  Any ideas what to start tearing apart?