Re: 1969 55 Horse Johnson shifting problem
Your motor has Hydro-electric shift. This is a shift system that uses electrical solenoids to move poppet valves in the gearbox. Those valves affect the flow of gear oil in a way that moves a piston and that piston, in turn, positions the clutch dog in either the neutral or reverse position, depending on what movement of the gearshift handle you have made. Application of power to one solenoid moves the system to neutral and power to both solenoids, moves it to reverse.
This system is spring loaded, so that the piston will move to the forward position, absent hydraulic pressure to move it to neutral or reverse. Although the pistons do jam sometimes, in all probability, your problem is electrical. The most common culprit is the shift switch in the control box. In the Johnson version, there is a toggle switch inside of the box - it contains both shifting circuitry and a safety cutout for the starting circuit.
If you'd like to PM me with an email address, I will send you a PDF of the control box chapter from a 1972 Johnson 65hp service manual. The '72 has the same shift system as your motor, so the troubleshooting info should be the same. That said, I highly recommend buying an OEM manual for your motor. You can do so right here at iboats.