Transmission rattle when idling

[jonahmulski]

I have a '76 Tartan TOCK with a 4 cylinder 80hp Ford Lehman with a Warner Velvet Drive hydraulic transmission. When idling the transmission makes a rattling sound but if I put tension on the drive shaft by squeezing it with my hand the rattling goes away. It also goes away once I raise the RPMs. Recently the boat was out of the water to replace a cuttless bearing that had slipped out of place and slid up the shaft (a product of poor instillation). While she was out of the water I changed out the folding prop that was on the boat when I bought it for the original fixed prop that also came with the boat. Once back in the water I noticed the sound. Unfortunately, I don't recall if the transmission noise was happening with the folding prop. The original owner said he had the prop serviced so I don't suspect it's out of balance, however, at this point everything is an option. Bent shaft, engine out of alignment...?
I recorded the sound (the pics are only there so I could get the movie online): Transmission sound video by jemulski - Photobucket
The beginning of the recording the RPMs are up around 1000 then it drops to idle and the noise starts, then I add pressure and it goes away.
Any thoughts would be really helpful! Thanks, Jonah

[djmarchand]

Sounds like the torsional damper is allowing the gears to rattle a bit at low rpms. You could replace the damper and it might solve it. Or live with it.

David

[roberttigar]

Velvet drives will normally rattle when engine is at idel speed and in gear-its the springs in the damper plate. When you accellerate to 1000 rpm, the plate springs press harder against the internal plate. If this raddling becomes excessive, it mean that the springs are broken and the plate needs to be replaced. Bob

[jstevens]

I am not a mechanic nor evenly mechanically inclined, so take that into account.

I think the two previous posters are correct, sounds like a damper plate issue. If this is a new sound, it could be a damper plate failure. I recommend you have the plate checked. Unfortunately this means pulling the transmission. As an alternative see if you can have the ATF analyzed for wear on the gear rings. What you are hearing is the idle engine pulses hitting the transmission without the damper plate absorbing them. When you increase the RPMs the pulses even out and the backlash noise diminishes or goes away even if the dampler plate is not functional.

If you go to the trouble of pulling the tranny, then you might as well replace damper plate, even if there are no signs of failure.

You could live with the noise, but at the risk of destroying the tranny or requiring a major rebuild. I would have it checked out.

I had a similar sound from my engine. After three years of living with the problem (I had several mechanics check it out) I ended up with a completely destroyed reverse gear ring and badly worn forward gear ring in my VD. Fortunately the planetary gear was not damaged and the VD could be rebuilt with new gear rings and a new oil cooler.

If you replace the damper plate you may have trouble finding an exact replacement for the one that was installed in '76. Many of the newer damper plates do not have springs. A newer damper plate may not fit the bell housing of your engine and could require shims that may move the transmission an inch so aft.

Good luck,

John

[GordMay]

See the excellent earlier discussion
➥ http://www.cruisersforum.com/forums/...oise-8919.html

and
Velvet Drive Owner’s Manual
Here ➥ http://www.google.ca/url?sa=t&rct=j&...0ln59g&cad=rja

Or ➥ https://docs.google.com/viewer?a=v&q...3-Xh-3Hy5GABnA

[jonahmulski]

Thanks for the information and the manual!
According to Alan Wheeler in the VELVET TRANSMISSION NOISE thread this transmission doesn't have a damper plate (unless I'm reading his discription incorectly). Question, "I understand that Alan, but doesn't the transmission spline shaft stab into a pressure plate that is bolted to the fly wheel?" Reply, "Not in this case. It's a little different. It's quite a cool box design actually. Very simple once you get your head around how it works. Not a great deal of moving parts and that is what makes it such a reliable box.
There are three main components. The input shaft assembly, the intermediate gear assembly and the output shaft assembly. Inside the Input shaft assembly and the intermediate gear assembly are clutch packs. These are very different to a pressure plate clutch system between an engine and gearbox in say a car. The packs are similar to what is in an autotransmision box in a car. The friction plates, of which there are 8 I think, spin in an oil bath slipping over slip plates. There are teath on the outer edges of the Friction plates that lock into an outer casing and the slip plates have teath on the inner edge that lock on the Input shaft. When a gear is selected, oil pressure forces a piston to squezze these plates together and they grab the slip plates and the shaft spins the outer housing turning another gear. Dependign on which set of plates are locked determins which gear spins thus causing the output shaft to turn left or right."
I'm going to check some of the vitals I should have checked before posting and I'll get back to you all.
Cheers!

[gjordan]

There seems to be a little confusion about damper plates here. Velvet Drives normally use a damper plate to connect the flywheel of the engine to the splined input shaft of the transmission. The damper plate looks somewhat similar to a car or truck clutch disk, but bolts directly to the flywheel. The center of the damper plate has springs (like a clutch disc) that absorb the engine impulses which makes life easier for the transmission. Before you do anything drastic, check the idle speed of your engine with a good digital tackometer. Dont trust the accuracy of your boat tack. I learned this lesson the hard way(expensive way) . I had a converted Mercedes auto engine in a steel boat. It was a very good reliable set up, but rattled like hell at an in gear idle. Being an uninsulted steel boat you could hear it for a hundred yards. I sailed like that for lots of miles, but hated manuvering in harbors becouse of the noise. At just above an idle it smoothed right out. I was told about bad damper plates by other cruisers and decided that I had better change it. I pulled the trans, and ordered a new damper plate from Florida. The old one didnt look bad to me, but I changed it anyway. The end result was the same damn noise. Finally I met a cruiser that had worked in a marine engine shop before cutting the dock lines, and he came over and listened to the engine, and said the idle is too slow. We set the idle up about 100 rpm and everything was smooth. It didnt make much differance on the slight clunk when putting it into gear and solved the problem. Becouse this was done with much sweating in the tropics it was a lesson I remember well. If it turns out that your idle is correct, I would still set it up a little to see if that solves it. If that doesnt solve it, go head on and start changing things, but I always try the cheep simple things first. Good Luck._____Grant.