I have a 1975 mercury 650 3cyl that needed a water pump and before I dropped the lower unit it shifted fine.Now it only has forward no matter what position the shifter is in.The shift rod in lower unit will turn almost a full 360 and if turned all the way to one side the rod will turn a bit more and the prop will turn freely in both directions.What could I have done to to cause this and how do I fix it? thanks for any help