Dual-mass flywheel: functions and symptoms

Dual-mass flywheel: functions and symptoms

Dual-mass flywheel: functions and symptoms

The dual-mass flywheel is an element present in many modern cars. Many people are unaware of this mechanical component until it breaks down and needs to be repaired, usually causing great expense to the owner. Next we will explain the functions it performs, how it works and the possible problems that this element can cause.

What Is The Dual-Mass Flywheel?

What is the dual-mass flywheel

To understand this concept we must first know what the flywheel of a car is. The flywheel is a part connected to the engine that stores the kinetic energy that comes from the engine. Thus, at the moment that this steering wheel stops receiving this inertia, it can maintain its movement and provides inertia so that the movement of the vehicle is smoother. The clutch disc is coupled to this flywheel to transmit power from the car’s engine to the gearbox and thus set the vehicle in motion.

There are single-mass flywheels, which are manufactured in one piece and are coupled to the starter motor. These ruffles are becoming less common.

On the other hand, the dual-mass flywheel is an inertia flywheel with two masses, as its name indicates. It is also known as a dual mass flywheel, this type of flywheel is usually more complete and effective. They are made up of two pieces similar to mono-mass flywheels, one of them is attached to the crankshaft and the other is attached to the transmission, but inside there is a helical spring and a ball bearing. These elements prevent the vibrations generated by the engine from reaching the gearbox and affecting the proper functioning of the vehicle by absorbing the vibrations of the engine at two points. Thanks to this, a more progressive disengagement is achieved and noise and vibrations are reduced.

Apart from eliminating vibrations from the mechanics, the dual-mass flywheel also has the manufacturer’s or mechanic’s references engraved to know the recommended setting. It also supports the electric starter motor, starting the crankshaft and transmitting power to it so that it makes the first expansion cycles. If the starter motor had to do this alone, it would wear enormously and would have to be replaced every two months.

At this point it is possible to wonder, in the case of our car, how to know if the flywheel is dual-mass or single-mass. The truth is, there is no exact way to find out except by checking with your manufacturer. It is true that most cars with dual-mass flywheel are diesel, but this does not assure anything since there are gasoline cars with dual-mass flywheels and diesel cars with single-mass flywheels.

Parts Of A Dual-Mass Flywheel

Parts of a dual-mass flywheel

The dual-mass flywheel is somewhat more complex than a single-mass flywheel due to its two component masses.

 Next we will explain the 6 pieces that make them up. 

  • Primary mass : The primary mass is attached to the engine crankshaft. The inertia of this combines with that of the crankshaft to form the same unit. The primary mass and primary cap form the channel of the arch springs. This channel is generally divided into two sections, which are separated by the tops of the arch springs.
  • Secondary mass : The secondary mass connects the DMF to the power train on the gearbox side. This secondary mass collaborates with the car’s clutch to transmit the modulated torque from the steering wheel to the gearbox. The dual-mass flywheel and the clutch are joined in this part of the flywheel by screws.
  • Bearing : The seat of this bearing is in the primary mass. It is in charge of joining the two masses and supporting the disengagement force applied to the flywheel. This bearing allows the masses to rotate with each other and allows a tilting movement in both.
  • Flange : Used to transmit torque from the primary to the secondary mass, that is, from the engine to the clutch.
  • Friction control disc : This component is only present in some models of dual-mass flywheel. It provides a supplementary cushioning in its operation.
  • Arch dock : It is installed in the dock channel. The coils of the spring slide along the guide thus creating damping.

Possible Problems In A Dual-Mass Flywheel

Over time, the components of the flywheel may deteriorate and wear out. The symptoms of failure in a dual-mass flywheel are mainly vibrations. The following explains in more detail how to tell if the flywheel is bad and the general symptoms of a DMF failure.

When you hear a metallic noise when you squeeze the clutch with the engine in neutral and running, which disappears when you depress the pedal fully, it is likely a problem between the clutch and the DMF.

In the event that we perceive an unbalanced vibration of the engine when idling, which can also be observed in the gear lever, it may be another symptom of a failure in the dual-mass flywheel. Sometimes this failure can also be confused with a failure in the injectors since the vibration is similar.

Another symptom of a DMF failure can be a metallic noise when the car engine is stopped, which is no longer heard when the engine stops completely. If the dual-mass flywheel is badly damaged, the noise can also be seen when accelerating. In these cases, the fault is likely to be serious and may have also affected the gearbox.

It is possible that when the dual-mass flywheel does not function properly, it may cause clutch collar or thrust bearing failure. In this case, the clutch pedal may be rendered useless since the vibrations of the dual-mass flywheel cause the hydraulic circuit to take in air and lose pressure on the pedal. In this case it is easy to confuse the problem between the dual-mass flywheel and the clutch.

What Happens If I Don’T Change The DMF?

From what we’ve already explained above, ignoring these types of steering wheel issues is not a good idea. If the flywheel plates come off due to broken springs, their force can seriously damage the gearbox and engine drive shaft. A broken gearbox and the other consequences of a broken DMF are a huge expense for the car owner. However, up to this point, the symptoms of steering wheel failure must be ignored for tens of thousands of kilometres.

The problem with driving with a bad dual-mass flywheel is that the vibrations from the engine are not absorbed and the rest of the components have to withstand a level of vibrations for which they were not designed. This leads to much greater wear on all parts.


The flywheel is an essential part in all cars. The type of dual-mass flywheel is increasingly used in vehicles due to its good performance. It is important to be aware of the symptoms to be able to know if the flywheel is bad and thus be able to fix the failure of the flywheel before there are more serious consequences.

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