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Old 27-06-2012, 08:20   #16
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Join Date: Nov 2011
Location: Moss Landing, CA
Boat: 41' Tartan TOCK
Posts: 44

Hi Alan,
I have another thread going about a noise in my Velvet Drive tranny, if you have a moment I would greatly appreciate your input. It seems you have a good understanding of these transmissions.
Transmission rattle when idling
Many thanks!

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Old 16-11-2014, 18:39   #17
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After you have checked to see that nothing is physically falling apart between the transmission and the propeller; At idle shift into gear and using a stethoscope(or a plain old stick) to listen at different spots of the drivetrain-front of transmission; usually a "clunk" noise is generated from the drive-plate or "damper" plate, it has two main parts. A disc built around a female spline fitting, and a larger outer disc which is bolted to the engine flywheel. The two discs are not directly joined to each other but have usually four or more compression springs fitted into the outer disc which drive the inner splined disc. these springs smooth the acceleration-deceleration jolts caused by firing- compressing cylinders of the engine and they take out part of the inertial shock of connecting a spinning engine to a not-spinning, or counter-rotating, transmission,shaft,and propeller mass. If you shift into gear, or from forward to reverse at too high an rpm you cause these springs to compress too much and it can break the springs, causing the damper to no longer "take up" these driveline shocks smoothly. Sometimes just normal wear slowly hammers the slot the spring is riding in out of shape, the springs can then rattle back and forth between their contact points with either disc, this can produce an audible "clunk" when shifting. There is a newer type of damper plate on the market called a Shure-drive. it does not use metal springs to absorb shock but uses multiple rubber caps on gear-type "teeth" attached to the transmission input-spline fitting. This rubber capped "gear" slides into a female notched ring bolted to the flywheel. It was invented by Twin-Disc Transmission I believe and is practically indestructible. It provides a quieter shift with much more shock absorbing area than the old spring damper and if the rubber cups ever do get damaged or worn they can easily (relatively-easily) be replaced! Noise from back of transmission; worn clutch plates in the transmission itself can produce a "clunk" also. these plates are steel plates, half of them with small teeth fitting on to the input shaft , the other half having outer teeth that fit into a "basket" attached to the transmission output shaft. As the transmission ages these teeth get worn and slack develops between the parts that turn them, and the parts that they turn, this slack can produce a "clunk" as it takes up also.

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