Tranny Jumping Out Under Load

Hey guys, new to the forum. I have an 84 nautique 2001, boat has over 1300 hours on it and has always ran great

Couple weeks ago after pulling wakeboarders for an hour or so with no problem I went to pull my brother up on the slalom and the boat jumped out of gear when I got on it. When doing some trouble shooting we found if we eased on the throttle we could make it all the way up to wide open turning 4K, but if we ever romped on with any torque it'd jump out of gear.
I checked the tranny fluid and it was right in the middle on dipstick, but saw a forum post from someone that said their tranny slipped anytime they ran it less than full. Since we didn't see anything else wrong after checking the linkage I ended up adding a quart of Dex III which put the fluid a little over the full line on the dipstick. That seemed to fix the problem for the weekend, ran it hard the next day, pulling skiers and boarders with a full load, regularly going straight from an idle speed to full throttle when pulling up bigger skiers and never had a sign of any tranny slippage.
Now, a couple weeks later, we took it out today, pulled up a couple slalom skiers and boarders with a full boat load with no problem at all. Then after an hour or two of boating went to pull someone up and she jumped out of gear again. Checked the fluid and it was still on the slightly over-full side. Waited a couple hours with the cover open hoping it would be alright after cooling off, but it would still jump out when romped on. Still was able to make it back across the lake to the ramp at the end of the day just fine by easing onto the throttle, but did notice that a few times it would sound/feel as if it was actually slipping, but not fully disengaging/jumping out.

When I say jumping out of gear, I mean like engine overrevving and boat falling on its face. And for what its worth, I did check the prop and it is still fine, even pulled it off to make sure the key hadn't sheered off somehow and it was fine as well.

Have found a few discussions about slipping trannys but haven't seen any with this sort of problem so I'm hopping to get some guidance on anything I could check into. I'm not familiar with these transmissions at all, but from what I've read, I understand they have some sort of pump mechanism for switching between forward and reverse, but was wondering if there was possibly a clutch of some sort as well, since that'd probably be a lot cheaper fix than a new transmission. Sorry for the needlessly long first post. Thanks for the help.

Unfortunately you are looking at a rebuild. Once they slip they are done. On the up side it is after all 30 years old and while 1300 is not a lot of hours it might have had some heavy duty use. The clutch plates are held under hydraulic pressure,the oil level needs to be checked right after you shut it down before the oil in the lines and cooler have a chance drain back.

Hey Gary S, I pulled my transmission tonight and left the engine jacked up under the exhaust manifolds, I saw posts of people doing it this way, but wasn't sure if they braced it up somewhere else also. Do you think the weight will be ok on the exhaust for a week or so while the tranny is sent out to fantastic finish marine? Thanks

It was too dark for pics, but here's what I copied.

Thats very clean.