Velvet Drive Knocking

My 79 Nauty is experencing a little knock coming from the transmition. I have the engine set at a low idle and when I put it in gear, forward mainly, there is a noticable knock or clatter from the tranny. The noise will disapear as soon as I give it more gas and the boat picks up speed.

Has anyone experienced this before?

The plate will cost you a $100 and take a day to put out and in.

I am cheap enough to run it till it breaks. Just keep the Lake Sherrifs phone# handy for the tow.

I would like to it out this weekend and inspect the situation. I've never taken the tranny from the engine, but it looks so easy to get to and that is what I'm afraid of. Usually these projects end up making me land locked for the summer.
What if I happen to run the vessel a few more times, and if it is indeed the damper plate, am I risking to break more parts within the tranny if the plate were to come all to pieces or is the plate isolated from other delicate parts?
I'm not ruling out the fact that it could be more servere than the plate, like another part of the tranny or like SKYHAWKFLYER suggested the prop saft(one which I will also inspect) but I am just trying to feel out what others have experienced.

I had the same issue with my 84 at one time. It was knocking and it turned out the damper plate was bad. It has a series of springs all around the plate on the outside. Most of the springs were broken off. Get it replaced ASAP. It will cause more damage as you shift in out of forward - neutral - reverse. Basically throwing direct force onto your gears in the velvet drive, rather than "dampening" the power and "sliding" it into gear.

cheers

I might take a look at my damper plate just for kicks to check it out. If I back out the velvet drive bolts can I get down into the damper plate area with a small mirror to inspect (without pulling the whole transmission). The springs break? Would I also be looking for pieces of spring at the bottom of the transmission housing?

OK, last sat. I removed the tranny and damper plate. My particular damper plate is very hard to inspect because the springs are not exposed, they have covers pop rivited over them. Well the plate is pretty rusty and seems to be locked up so I ordered a new one today.
Since I was unable to justify the noise was coming from the damper plate, I bought a coupling to join the two hydraulic hoses while the tranny was on my work bench. Then I proceeded to attach my electric drill to the input shaft. I gradually increased the speed of the drill and never heard a noise. Even with my father holding the output shaft to add some resistance the velvet drive operated smooth as ever.

So this made me more comfortable in putting the blame on the damper plate. I will install the new plate this weekend and post (hopefully) some good news.

Same deal... Its usually only when you are in gear.. I had an 84 with the same problem I thought it was my whole transmission.. so I took it a dealer and they pulled it apart and found the plate was bad (all the springs rusted off) Total job for the dealer was $500.. $150 for the part (PCM plate) and the rest was labor. Have to take the whole tranny out, replace the plate and put the tranny back in

Was there any alcohol involved???

After a engine rebuild, new tranny and flex plate, and prior to final tuning my flex plate growled and made me think somnething was wrong internally to transmission. Woody at SECC told me that after the final tuning the noise would go away and he was 100% right. Are you sure the engine is not slightly out of tune? A quick timing check and maybe take a look at how steady the vacuum reading is could shed some light and allow you to sleep easier.