"I have never read the "ma
"I have never read the "manual" but I can tell you how I go about this.
First, did you only have reverse -- that is not even neutral? Did it shift into reverse and out only to neutral? At different times, I have had both upper and lower shift cable problems.
If there is no shift action at all, it could be a loose connection or a broken cable. Check cables first. Does moving the shift lever actually move the shift mechanism in the engine compartment? If not the upper shift cable is loose or broken.
If the upper cable is intact, disconnect the lower shift cable from the mechanism in the engine compartment. Manually move the lower cable fore and aft to determine if anything is happening at the drive unit. A helper is handy to slowly turn the propeller as you move this cable. It should engage at each end of travel, with a neutral obtained between these positions.
If you can detect all three gear positions and cables seem to be intact, put shift lever in neutral position, manipulate the cable back and forth until confident you are in neutral, spin the adjuster in the engine compartment until the mount is aligned with its keeper and lock it down again. Hook up flush water and try it with engine running.
If you cannot detect forward, neutral, and reverse gear engagement, the lower shift cable could be disconnected at either end, or broken and require replacement. Or the shift slide bar could somehow be broken or disengaged. If cable is broken you may find it pulling out into your hand. At this point you are probably going to have to pull the lower unit to replace the lower shift cable, or reconnect something. Worst case scenario is that the mechanical shift mechanism is broken or a gear stripped.
Someone may have a printable reference."