Frequently Asked Questions

How does a Dual Mass Flywheel work?

Well it's basically a ring inside another with a 'spring' between them that takes out the vibarations/judder associated with a normal clutch setup'

Modern engines can be driven at extremely low rpms. The trend is toward ever increasing engine torques. Wind-tunnel-optimized bodies are creating less wind noise. New calculation methods are helping reduce vehicle weights and weight-saving concepts are boosting engine efficiency as well. The addition of a fifth or a sixth gear can also reduce fuel consumption. Thinner oils are making precise shifting easier. In short: The sources of noise are increasing and natural damping is decreasing. What has remained is the principle of the internal combustion engine whose cyclical combustion processes excite torsional vibrations in the drive train – the unpleasant consequences of which are gear rattles and body booms.

Drivers who are accustomed to increased comfort no longer accept such background noises.

The job of the clutch is now more important than ever – in addition to engaging and disengaging, it must effectively insulate the engine’s vibrations.

Physically, this is easy to solve: The mass moment of inertia of the transmission must be increased without increasing the mass to be shifted. This dampens the engine’s torsional vibrations and brings about the desired comfort level. The process reduces load on the transmission at the same time.

Dual Mass FlywheelThe dual mass systems are designed to transmit less engine vibration to the drive train, and give a better more car like driving experience. They also reduce some of the jarring and stress on the transmission and remainder of the drive train.

They work fine as long as the engine remains unmodified and the vehicle is not used/abused beyond manufacturers recommendations.

As soon as you start to increase the engine power over manufacturers guidelines, or load the vehicle beyond design parameters, you run into problems.

Dual mass flywheels are tuned systems and must be matched to the engine torque curve, engine resonant characteristics, vehicle load curves (including axle ratio/tyre size calculations).

They work by having a set of springs inserted between two rotating masses (thus dual mass). The springs are sized to soak up some of the resonant vibration from the diesel engine under load conditions.

A dual mass fly wheel generally also contains an over torque friction release, so if it gets suddenly overloaded, rather than damage the springs, it slips.

This works fine as a safety valve, but if it does it much it burns up. In short, overloaded they burn up and the springs get destroyed and they are worse than if it were a single mass FW.

The single mass part WILL tend to transmit more engine pulse (vibration) tot he drive train, and will seem a bit rougher. But it is straight forward to design a single mass flywheel and clutch package for pretty much any engine torque curve and vehicle loading combo you can come up with.

It does drives more like a Van or Lorry, but has much better reliability at extreme use levels.

Lets look at a video which explains it visually:

Now a normal clutch has the 'springs' built into it. Again here is another video to explain how a 'normal' clutch operates

This FAQ was compiled from various web sources

Info 15 April 2009 by Dave_Retired.

C4 - DS4 Owners