Re: 15hp Johnson Outboard:Reverse does not engage
Most likely thing is that the shift rod needs adjusting or tightening at the engine end. The shift rod is pushed downward to engage forward gear and pulled upward for reverse. If it is not tight and properly adjusted, it will not pull far enough.
Copy this link to your browser without the quotation marks, It may help.
"http://www.wisnersinc.com/fishing%20Info/lower_unit.htm"