Power Plus 1:23:1 noise

Hello-
Can someone who knows the transmissions and drive systems on these boats, please have a quick read below and let me know if I'm understanding this correctly. My boat is a 99 Air DD with a GT-40.

The issue
There is a rapid paced "rer,rer,rer,rer,rer,rer" noise in neutral coming from the rear of the motor/tranny area. I've narrowed it down to either the clutch or dampener plate. These 2 parts transfer power between the engine & the transmission. The major part flow from front to back is as follows- engine/crankshaft, flywheel, dampener plate, clutch, transmission, drive shaft/prop.

Dampener plate- (part cost +-$100)
This plate bolts to the flywheel and has springs in a circular pattern. It engages the clutch as the boat is shifted into gear. Sometimes this plate becomes loose and/or the springs become unseated and can cause a noise like I'm experiencing. It only does this in neutral because the plate is not engaged to the clutch/tranny and is only spinning with the flywheel, possibly knicking the clutch plate & causing the noise. When the boat is shifted into gear, the noise goes away because the plate is firmly mated with the clutch/tranny. If the spring(s) become completely unseated or the dampener plate loosens entirely from the flywheel, all heck breaks loose and you're stranded on the lake.

Clutch (part cost +- $200)
There are circular clutch plates between the dampener plate and the transmission that are the final transfer of power between the engine and the transmission. If the tranny ever heated up for whatever reason (usually low or dirty fluid) these plates can warp and cause the same issue. Instead it would be a warped clutch plate being knicked by the dampener plate in neutral. The way to test this is to start the boat on the trailer and visually check if the drive shaft/prop is turning. If it is turning, the clutch plates are most likely warped and being knicked by the dampener plate while it's spinning in neutral. If the drive shaft/prop are NOT turning, the noise is most likely coming from a faulty dampener plate.

The noise is most likely originating from this point, whether its warped clutch plate(s) or a faulty dampener plate. The best way to determine which part is causing the problem without tearing into the tranny is to inspect the drive shaft/prop while the boat is running on the trailer in neutral, as described above.

Thanks again for any help.

Thanks Kristof. Much appreciated for taking the time to pass me to the right person. Look forward to Erik's response.

Maybe working overtime on Nautiquechick's tranny!

gd damn, that ones way out there...
damper, as what it says, dampens torsional or cushions torsionals, anytime the engine is running the damper is spinning and spinning the input shaft of the transmission.

it takes roughly 900 degrees to warp a clutch plate and steel, nothing on an engine gets to 900 degrees, (except in the heart of the combustion chamber)these are wet clutch plates that run in an oil bath inside of the transmission relying on coefficient of friction to keep them from slipping, they rarely slip at idle and need a reason to slip, IE., low oil, worn pump, hard seals. wet clutch plates do not wear like a dry clutch and need adjusting. I'm not saying they don't wear, they actually do but only a couple of thousandths and many hours. Basically a transmission operates on hydraulic theory, pressure behind a piston that pushes against internally splined clutch plates and externally splined steel plates staggered normally in order of steel, clutch, steel, clutch, and so on, the more the plates the more the holding capacity, the bigger the piston the more psi, on the clutches and the more the oil pressure the better the hold.
I get asked all the time, why don't these transmissions have a torque converter?
the slip is at the prop and power transfer is a true 1 to 1, unlike a car that has a solid object hitting the ground which is referred to as a tire, on a car it is truly locked in gear but the converter does the slipping and has no mechanical connection thus letting the car sit and not stall and a good example with a boat would be to back it into a sand bar and throw it in gear, the end result would be the engine would stall because it is a true mechanical connection, if it had a torque converter it would allow the slip and wouldn't stall the engine. A good way to imagine a torque converter would be to take 2 fans and face them towards each other and turn one on, we all know what happens, the other fan starts to turn... this is exactly how a converter works, instead of air though the basic principle is still the same with oil

so, change your damper and it will fix your problem and don't try to figure this stuff out because it is mind boggling

Just to make sure you do say above it happens in neutral, correct? Cause while in gear the 1:23:1 typically does makes a high pitch squealing noise. That is how I know my shaft is turning :)

the one thing about a PCM trans is you may get some planetary noise in neutral, they are spur cut, not bevel cut and spur (straight cut gears) have a tendency to whine and another good example of spur cut gears are in an automotive application. on a standard shift car if you ever noticed backing in reverse you will get a whine and it will at times grind when shifting the trans into neutral, the reason is reverse does not have a synchro on it to speed up the gear to get into the next speed so the engineers cut the gear straight in order to slide the idler (reverse gear) into the cluster gear. and that is what you hear whining on reverse. The pcm, unlike the borg warner uses all straight cut gears (except in the tail section of the 1.23's) but for the most part you are probably hearing some neutral gear whine and it is being aggravated by a weakening damper.
the damper is a crucial part of the drive line, its job as another analogy would be to take a coil spring from a car and weld a flat plate on top of it, and then take a jack hammer and stand over the spring and nail it with the jack hammer, the springs will absorb the shock of the jack hammer, but after time the spring will weaken or crack and will start to hit the other coils and start rattling...this is what happens with a weak damper, with out the damper the jack hammering effect would be transmitted right into the transmission, and you know what happens when you hit the jack hammer on solid concrete..something breaks

Thank you so much everybody. Yes, I was thinking autoshop. Bad news though....I pulled allt he tranny fluid out and found it not to be clear. Dirty and kinda pink in color. Like water had been mixed with it. I am planning on running it this weekend to see if the trannt fluid gets contaminated with water again. If so, most likely tranny cooler? Not even sure if this has anything to do with the neutral noise whick sounds like it's coming from the bell housing. Again, the boat drives perfect and the prop&shaft are still on the trailer when running, able to turn with normal hand pressure. Crap. kinda at a new stage. hate to teardown and rebuild a transmission that works perfectly, a pink frothy mix in the tranny's now good. And then there's the neutral noise that seems to be a damper plate. I know the normal nautique whine in gear which is there and fine. Any suggestions?

Thanks again for all the help and advice.

mike

Mike,
Before you take the chance of damaging the trans more that it potentionally is, pull the trans cooler and pressure test it. Find the source of the water. Then do a couple oil changes on the trans to get rid of the water.

well spoken eric