I just replaced my impeller. (my first time). While the lower unit was off i believe somehow it got shifted out of forward gear. the maual says to shift motor into forward gear before dropping unit which i did. when i put the unit back on I only had forward gear, even when i shifted in reverse and neutral(the motor also would start while in gear). So i took the lower unit off again and messed with the shifter and found forward and reverse tried to put it back on and had the same problem. I did this a third time only this time i shifted the motor to reverse and reinstalled it. now i seem to have forward, neutral and reverse. But to get it to shift into reverse I have to twist the prop shaft a little or it won't engage. What did I break? Any ideas? I could not hear any grinding while running it on muffs? The difficult shift into reverse is new. Any thoguhts?