470 slipping out of gear?

Hi All, I am new here, I do reference thie site frequently though now I have a problem I hope someone can help me with.
I have a 1980 Viking 22' with a 470 in it. It was just rebuilt last year, it still has less than 20 hours, so I'm still breaking it in.
The outdrive is about 3 yrs old. Yesterday when running out at around 2000 - 2500 rpm the engine revved up like it went into neutral, I pulled back on the throttle and slowed down, put it back into forward and away it went only to have the same thing happen a few minutes later. We shut it down and fished for a few hours with the kicker to let it cool down. When I started it up again and tried to go it would not shift at all fwd or rvse, but it would rev up. There was no noise when it happened it just seemed to slip out of gear. Thankfully my buddy was out too and we got a tow in. The prop is tight and looks ok, and the shift cable seems to be moving properly. I've heard possibly the prop or the hub, the prop being the lesser of the two evils. I'ts still sitting in the water, so I haven't looked at it closely yet. I was out on Lake Erie so I'm sure I didn't hit anything as I said there was no noise at all. How do I determine what the problem is?
Any suggestions would be greatly appreciated...
Thanks, Knot

Re: 470 slipping out of gear?

pull the boat and check the gear oil in the drive for proper level and condition

Re: 470 slipping out of gear?

Bt Doctur said:

pull the boat and check the gear oil in the drive for proper level and condition

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Yes I will do that, but it was just professionally rebuilt and put back together with approx 12 hrs on it.

Re: 470 slipping out of gear?

Start it up and look behind the engine to see if the driveshaft is turning. If not, probably your coupler. Do not run it very long if it is not turning or you will overheat, because the impeller is not turning.

Re: 470 slipping out of gear?

Check what stonyloam mentioned and also the hub on the prop, it could be slipping up on you. We had something like that happen last year with our 3.0 and a new prop fixed it.

Re: 470 slipping out of gear?

Thanks for the replies.
I sure hope it's the prop and not the coupler. big job right? If it is the coupler could it be caused by not alligning the engine properly when they put it back in?
I'm going to pull it out this week and take a look.
When it happened to your 3.0 did it still shift into gear? When I push the throttle forward or back it doesn't shift it's just smooth and after a certain point revs up.

Re: 470 slipping out of gear?

When it happened to my dad's 3.0 it still shifted into gear. Reverse doesn't like to lock in if it's trimmed up too far. Yes if the engine isn't properly aligned the coupler will get ruined.

Re: 470 slipping out of gear?

Pulled it out yesterday and yes it was the prop, the insert was totally gone, replaced it and good to go again, I'm very happy it was a $100 fix whew!! Thanks for all the help everyone, hope this might help someone else out.