prop on pontoon making a clunking noise

[jr2int]

I have an 1988 Mercury 80hp on a pontoon boat. My grandson was driving it when suddenly at about 3000 rpms it makes a "clunking" noise as if the prop has slipped on the hub. I pulled it out of the water and replaced the hub and thrust washer. I then put it back in the water and it still does the same thing. I would greatly appreciate any help any of you can give me on this. The prop is a 14x13p. Also, as far as I could tell the old hub and prop didn't appear to be damaged.
Thanks,
John

 

[steelespike]

Speaking generically sure sounds like a bad clutch dog.It clunks like you hit something.
There is a slim chance the shift cable is worn and not getting fully into gear.
On some motors you can unhook the shift cable and shift be hand. If the cable is bad it should shift ok by hand.
Probably not the easiest thing to test on a pontoon.

 

[WIMUSKY]

Moved to the Merc section since it doesn't seem to be a prop issue.....

 

[jr2int]

Thanks so much for your input steele. Is a clutch dog are tough repair? I'm not that familiar with lower units.....