FLY-WHEEL
A flywheel is a mechanical device specifically designed to efficiently store rotational energy. Flywheels resist changes in rotational speed by their moment of inertia. For example, flywheels are used in reciprocating engines because the active torque from the individual pistons is intermittent. Energy storage systems.
Dual Mass Flywheel
A dual-mass flywheel (DMF) is a rotating mechanical device that is used to provide continuous energy (rotational energy) in systems where the energy source is not continuous, the same way as a conventional flywheel acts, but damping any violent variation of torque or revolutions that could cause an unwanted vibration.
What is a Dual Mass Flywheel, and What does it do?
The dual mass flywheel is primarily designed to reduce noise and vibration. The DMF is sort of a mechanical "sponge", where vibrations and harshness in the driveline are dampened by two flywheel masses that are connected to one another by a series of high strength springs. Any roughness is absorbed (at least partially) by the springs between the flywheel masses. It may help to think of a dual mass flywheel as a shock absorber: each flywheel is a solid connection, but between there is a "soft" spring that takes some of the jolt out of accelerations, gear changes, etc.
How do you know there is something wrong with the flywheel?
When the clutch slips whilst   driving.
When you cannot change gear.
Transmission makes an unusual noise   whilst engaging/disengaging the clutch.
When the starter motor struggles to   rotate the flywheel.
When  should you consider a  flywheel replacement?
A flywheel replacement is normally recommended when changing the clutch. In most cases one will find that when the clutch is worn or damaged it may have affected the flywheel. Not replacing the flywheel at the same time may then lead to damage to the new clutch. Hence the need for a replacement at the same time, which is recommended by most mechanics.
Signs of juddering or vibrations when depressing clutch pedal are normally a sign that there may be something wrong with the flywheel, especially if problems appear in first gear. Apart from that, the flywheel's starter ring gear (the teeth around the out edge of the plate) can get damaged due to wear. Sometimes a tooth will break, preventing the starter motor's gear to grip properly leading to starting problems on the car.
Of course, if you suspect that you may need a flywheel replacement but are not sure, it is advisable to have Many Autos assess the situation first. In any case, always make sure to follow the manufacturer's guidelines.
