1978 mercury 115 hp stuck in reverse

[Turkey45]

I have a 1978 mercury 115 hp outboard that when in driveway starts, runs fine through forward, neutral, and reverse, but when i put it in the lake and in reverse it locks up the motor and will not come out of reverse. I can pull it out of the water and turn the prop by hand (with some trouble) it ticks and works fine then.
The last time it did it I rebuilt the lower unit (gears, bearings, seals, shifting dog and impeller). Any help would be greatly appreciated.
Thanks in advance!

 

[jimmbo]

When you are rotating the prop by hand I hope you are unhooking all the plug wires and grounding them. As for the shifting issue, misadjusted shift cable and/or improper preload on the throttle cable can cause shifting issues. Try disconnecting the throttle cable and see if it will shift to neutral.