6MT Gear Rattle - Answer
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6MT Gear Rattle - Answer
6MT has a dual-mass flywheel (high performance)... that said read information below (This applied to gear noise (rattle at idle):
The original dual-mass flywheel does one thing very well - exhibits inertia. It is more difficult to change the speed of the dual-mass flywheel, whether accelerating it or slowing it down... that means besides inhibiting engine acceleration to some degree, it also inhibits the deceleration that occurs between every power pulse. The power pulse transition is smoother, therefore no rattle.
A single-mass flywheel is the same sort of design as a solid aluminum lightweight flywheel: a rigid disk of metal, either aluminum or steel. In the OE applications, these flywheels are equipped with a sprung-hub clutch. The sprung-hub clutch "splits thte difference" between the these situations. The friction material (the disk itself) is not "hard coupled" to the hub, but has a springy nature to the assembly. It has a suspension, the springs you see around the hub. What this accomplishes is letting the power pulse couple the transmission's internal parts softly, and then de-couple softly. ("Softly" being a relative term here, it is just a few millimeters of travel, nothing that can be felt.) The net result is the difference between banging two pieces together and gently placing them together.
This clutch design has a center section that is separate from the outer friction area, with a flexible coupling mechanism that uses springs to cushion the power pulse variations. Sounds very similar to the dual-mass flywheel mechanism discussed earlier for a very good reason; the idea is exactly the same, but moves the power pulse variation absorption mechanism to the clutch disk itself.
The issue with gear rattle is that conventional lightweight flywheels retain the car's original solid-hub clutch disk. First, the lightened flywheel has less mass to damp the power pulse variations. Second, there is no mechanism within the solid-hub clutch disk to absorb the power pulse variations. The result is that a conventional lightweight flywheel with solid-hub clutch may create a noticeable amount of rattle. There is simply no cushioning action at all. Note that this gear rattle only occurs at idle, in neutral, with the clutch let out. It is not heard at any other time. Above idle (even just a couple hundred rpm) and the increased frequency of power pulses outpaces the speed at which the components couple/de-couple, therefore no rattle whatsoever.
The original dual-mass flywheel does one thing very well - exhibits inertia. It is more difficult to change the speed of the dual-mass flywheel, whether accelerating it or slowing it down... that means besides inhibiting engine acceleration to some degree, it also inhibits the deceleration that occurs between every power pulse. The power pulse transition is smoother, therefore no rattle.
A single-mass flywheel is the same sort of design as a solid aluminum lightweight flywheel: a rigid disk of metal, either aluminum or steel. In the OE applications, these flywheels are equipped with a sprung-hub clutch. The sprung-hub clutch "splits thte difference" between the these situations. The friction material (the disk itself) is not "hard coupled" to the hub, but has a springy nature to the assembly. It has a suspension, the springs you see around the hub. What this accomplishes is letting the power pulse couple the transmission's internal parts softly, and then de-couple softly. ("Softly" being a relative term here, it is just a few millimeters of travel, nothing that can be felt.) The net result is the difference between banging two pieces together and gently placing them together.
This clutch design has a center section that is separate from the outer friction area, with a flexible coupling mechanism that uses springs to cushion the power pulse variations. Sounds very similar to the dual-mass flywheel mechanism discussed earlier for a very good reason; the idea is exactly the same, but moves the power pulse variation absorption mechanism to the clutch disk itself.
The issue with gear rattle is that conventional lightweight flywheels retain the car's original solid-hub clutch disk. First, the lightened flywheel has less mass to damp the power pulse variations. Second, there is no mechanism within the solid-hub clutch disk to absorb the power pulse variations. The result is that a conventional lightweight flywheel with solid-hub clutch may create a noticeable amount of rattle. There is simply no cushioning action at all. Note that this gear rattle only occurs at idle, in neutral, with the clutch let out. It is not heard at any other time. Above idle (even just a couple hundred rpm) and the increased frequency of power pulses outpaces the speed at which the components couple/de-couple, therefore no rattle whatsoever.
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