slipping transmission

I'm visiting my folks in Iowa for the 4th and was hoping to fix a problem on there '55 Century Resorter. For years if there was a big load on the engine the transmission would slip, now if we run up above 2000 rpm it spins. The marina when they got it ready for summer said the fluid level was fine. I'm attatching pics as I can't even tell where to check the oil on this. Eric you've bailed me out before, I'm hoping the adjustment is just out of whack and you can maybe explain how to adjust the set screw on this thing. Any help would be great.

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Under the cover, you will find a rather large threaded drum. Its held in position with a special bolt with a un-threaded end that engages into notches around the outside. You may have to rotate the drum by hand to find this threaded pin. Remove it and using a piece of wood to prevent the small section from turning and tighten the outside section ONE notch. What you are doing, is removing some of the clearance between the clutch plates. I think once you get it opened up, you will see how it works. Don't worry about the reverse. I have never had to adjust it!!

The marina who simply stated that the "fluid" level was fine are F***ING idiots. Run do not walk away from them!! The boat is too valuable for someone who doesn't know what they are even looking at touch it. The "fluid" in the trans is engine oil. It's common to the engines crankcase.

Please go back in and edit your post using the enter key between your pictures.

Edit: Captleisure, Your statement stating that the trans has been slipping for years is bothering me. I can see a younger person picking up a beater ski/wake boat and not being concerned about what happens to the boat but I'm shocked that your parents would treat a wood classic in the same manor. Don't they care about it?? Wood boat owners do not treat their boats this way.

Captleisure, Sorry I got so wound up but when I heard that the slipping issue has been going on for that amount of time (even just a couple times per summer), I get concerned!! It really sould have been adressed a few years ago especially since it's such a simple and common adjustment. BTW, your folks should have a manual on the engine. If they don't, www.marineengine.com has them. One thing about the old Chrysler manuals is they are the most detailed (with pictures) I have ever seen!

Open it up when you get there and like I said, I feel the adjustment will be quite obvious to you. Just keep thinking that you want to reduce the clearance between the clutch plates. The extra arm above the shift arm on the outside is the reverse. Don't goof with it unless you have a problem. You don't want the reverse band grabing when you are in forward or neutral!!

Where are they in Iowa? There is a very good chapter of the ACBS around Clear Lake.

Pete that was it to a tee, I moved it one notch put it back togeather and the boats running around the lake like new. Cant thank you enough. To your earlier question my folks live on Clear Lake and belong to the ACBS it was one of those things that came up so infrequently they never thought to do anything about it until now when it was an issue.
Eric thanks againg for your quick response and contact info, i'm glad I didn't need to bug you I'm sure someday one of the bands will break and it will have to come out, can you still get parts for this? It holds 10 qrts of Oil not a project I'm looking forward to.
not sure of the make I think it may be a chrysler marine tranny, the canister is a combination oil filter/cooler.