I have a 1968-ish Mercury 110 9.8 hp and I recently repaired the impeller so that the cooling system would work properly. After I got everything reassembled ibtested the motor in a water barrel to make sure it was properly cycling water and while it was running it would not switch into gear, the selector would move as it should but the prop never engaged into forward or reverse. When I put it all back together the selector was in neutral as was the transmission shaft, what did I do wrong?