Dual-Mass Flywheel

  • Dual-mass flywheels are used in vehicles with manual transmissions
  • They provide vibration dampening in contrast to typical flywheels
  • Wear can be identified in a flywheel by measuring the rotational freeplay and sideways play
  • There are multiple ways to identify that a flywheel is failing

What is a Dual-Mass Flywheel?

A dual-mass flywheel (also known as DMFW or DMF), is a mechanical device that rotates and is used to generate continuous energy in systems where there is no continuous source of energy. Its operation is very similar to that of a regular flywheel, but it dampens any revolutions or torque that could produce any vibration. This is due to the fact that it has two flywheels separated by springs as opposed to just one flywheel.

The DMF acts as the direct contact between the clutch assembly and the engine in vehicles with manual transmissions. The reduced vibrations stops vibration in the powertrain system, which lets the engine run quieter, smoother and prolongs the lifespan of the transmission.

Dual-Mass Flywheel closeup

The Downside

There are some notable cons when dual-mass flywheels are used. DMFs have higher maintenance costs than the single-wheel version, with the flywheel generally needing to be changed when the clutch is being replaced, it adds time and money for the driver when this repair needs to be done. Manufacturers are working on making the replacing of dual-mass flywheels more affordable in recent times.

This is due to the DMF absorbing a lot of vibration, and therefore they are subject to wear. This should always be checked when the clutch is being replaced, as it is a good opportunity to be able to inspect the flywheel fully without obstruction. Some common warning signs of flywheel failure would be deep grooves and damage on the clutch mating surface, cracking and loss of grease.

How To Spot Wear on a Dual-Mass Flywheel?

There are two main signs that a DMF is worn and nearing the end of its lifespan. The first is the rock (sideways play) that can be felt in the flywheel. This can be tested by “rocking” the flywheel from side to side and observing the amount of play there is. The second way to test the flywheel is observing the rotational freeplay that is in the flywheel. This is the distance between when the secondary plate is moved all the way to the left and then to the right. There are specifications for this distance but a common rule of thumb is that if it is over an inch, then it is time for the flywheel to be replaced. The same wear limit specifications can also be found for the rock in the flywheel.

How Do I Know If My Dual-Mass Flywheel Is Failing?

There are some obvious signs that anyone with any level of mechanical knowledge can identify, and these can be very important to know as it can prevent flywheel failure while driving! If you experience one of these symptoms it would be advisable to get the flywheel checked out as soon as possible:

You Can’t Change Gears

This may sound obvious, and you definitely shouldn’t drive a car if you can’t change the gears, but if you find that you cannot change gears, then the flywheel is most likely in bad shape and should be replaced immediately.

Burning Smell

A burning smell is never good when driving, and it could have many different causes. A flywheel that is in poor condition could be the cause of a bad smell as there could be friction in the clutch.

Slipping Gears

If you change into a new gear and the car’s RPM increases faster than the ground speed, the gears are slipping. This can be due to a slipping flywheel, as there may be oil or something else on the surface of the flywheel that is preventing the clutch from gripping it properly.

Engine Stalling

A flywheel installed that is too light for the car will cause it to stall much more easily, and give it a rough idle. The car can be stalled just by pushing the clutch in as the engine speed drops too fast for the ECU to compensate.

Engine Vibrations

The powertrain could begin to vibrate if the flywheel is unbalanced. A loose flywheel is very dangerous and with the considerable weight of the flywheel it could start shaking the whole car.

These are just some of the signs that your dual-mass flywheel could be failing. If you notice any discrepancies with your car you should always get it checked out by a qualified mechanic. In general, most dual-mass flywheels last around 100,000 miles, however this is a very general estimate and it is not uncommon for flywheel failure to occur before then.

What experience do you have with dual-mass flywheels? Let us know with a comment down below!

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