DUAL MASS FLYWHEELS: What are they and why are they so much trouble? 


Basically it's a flywheel in two concentric parts or two facing flywheels stuck together with flexible compound to damp down transmitted vibration from diesel engines, improve gearchange quality and protect transmissions from torque reaction at around 2,000rpm, particularly the change from first to second.


What seems to happen is excess temperature from drivers riding their clutches affects the compound.

The result can be poor starting and running from the timing taken from the flywheel.

Poor starting from the starter motor engaging on the starter ring on the flywheel.

And failure of drive, blamed by dealers as clutch failure and charged for as clutch failure, when really the lack of drive is because the two parts of the dual mass flywheel have separated.

Van specialists weld together the two parts of the flywheels of Transit vans to prevent separation trouble, but this leads to very rough running.

Here is a Scotia Inspections engineer's report on a failed Dual Mass Flywheel in a Peugeot 407 diesel:

The dual mass fly wheel was still in situ. The engineer could move the fly wheel back and forth, clearly the unit had excess movement between the primary and secondary flywheel on the 8 centre bolts, the fixing stud holes had clearly excessively stretched. The dual mass fly wheel in this state would have caused the unit to audibly rattle and eventually break up, failing in service. The release bearing has also failed.


Requires a replacement Dual Mass flywheel assembly, clutch and release bearing.


A Dual Mass Flywheel is basically two components (the primary & secondary mass) linked together by a damping mechanism within the secondary mass and located by the central carrier bearing. The damping mechanism is there to absorb the torque loads of the crankshaft and to help deliver a smooth transfer to the road wheels via the clutch.

As time passes and the vehicle's mileage increases the damping mechanism softens and weakens. As the mileage increases the damping mechanism becomes weaker to the point where the movement between the primary and secondary masses becomes excessive. When this happens the flywheel tends to vibrate or rattle when driving. In this case the description of the complaint, the excess movement of the secondary mass and the indicated mileage of 31,653 miles would suggest that it has reached the stage where it has started to vibrate causing a knocking sound from within the bell housing.

Having carried out an inspection to the flywheel of this vehicle it is our opinion its condition is due to wear. The excess rotational movement between the Primary & Secondary Components of the Dual Mass Flywheel together with the movement at the central location bearing is a strong indication that the damping mechanism within the flywheel is worn, given the low mileage the vehicle had done since the inception of the policy leads us to believe that the wear would have been present at this time all be it to a slightly lesser degree, progressing to the point we are at now


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