1988 mercury outboard won’t go into reverse?

Bit of a stumper,I just purchased a boat with a 1988 mercury 100 hp motor on it, I had him hook up the ears on the motor and tested it.
It ran great, went into forward and reverse fine, no grinding or difficulty getting into gear. Brought it home and hooked up the ears and it worked fine, went to the lake yesterday and put the boat into the water and it would not go into reverse ( sounded like it wanted to, but just not quite ).
Ran it around the lake in forward and no problem, tried reverse again and no go.
Brought it back home and put the ears on and reverse worked fine. Good stream out on the pee hole.
Just wondering what this could be?
Thanks
Don

Maybe the pressure/resistance on the prop from actually being in the water is causing the problem. Does reverse work well with the motor trimmed up? If so there may be some slop that is allowing everything to fall into place when trimmed up a little and no resistance. And then when the motor is down fully the aid of gravity isn’t there and the gears aren’t aligning properly. Hope that makes sense!?

Had a buddy with an 80 or 90 hp from the same era that had reverse go on him. Got parts from Twin City Outboard for a very reasonable price and works great since! Hope this isn’t your issue though.

Sounds like the linkage may be off a little. I do know that the linkage could definetly be off by that much. Haven’t actually worked on this myself so hopefully someone else that’s smarter than I am can chime in.

Does the handle go into position and the boat just doesn’t go? If so it could be the reverse clutch, hope not though. When at the lake can you watch the prop while someone else puts it in reverse? I would think if the hub was spun you would have lost forward also.

Also a good idea as mentioned above to verify the linkage, maybe the cable has just stretched out over the years.

Thanks guys, I will try the linkage adjustment . Just seemed odd that it worked fine in the driveway.
Thanks
Don

I had that happen to a Mercury this spring. Testing it in the driveway it spun in reverse, but in the water the resistance that water created made a grinding noise not allowing it to get all the way into gear. It turned out to be the shifter cable was bad. I tried to adjust the cable, but it didn’t have enough movement anymore to be able to get into both forward and reverse. A new cable cured it. If you replace one cable you may as well replace the throttle cable too at the same time. $75 for both cables.

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Thanks guys, I will try the linkage adjustment . Just seemed odd that it worked fine in the driveway.
Thanks
Don

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