Clutch Industries - Australia's world class clutch manufacturer

Conventional Flywheels

The flywheel’s role in a vehicle is to do the following;

  • Provide a flat clamping surface for the clutch plate to match up to.
  • Keep momentum; it’s a heavy mass that keep the crank turning
  • Take heat way from the clutch disc/plate, acting as a heat sink

Because the flywheel is bolted directly to the crank, the flywheel will always spin at the same rate as the crank shaft of the engine. Around the outside of the flywheel you will find a ring gear. Although it is part of the flywheel, ring gears have nothing to do with the clutch itself. They work with the starter motor.

Grinding or replacing a flywheel

When a new clutch kit is installed the flywheel must be either replaced or ground. This is because excessive heat from normal driving changes the structure of your flywheel surface which creates less friction affecting the performance of your clutch. If this is not done common issues experienced are shudder and or slipping after installing the new clutch kit.


Why grind when you can replace?

There are three main technical reasons to replace a conventional flywheel instead of grinding it.

  1. Issues caused by a bad grind. There are various issues that can come out of a poor grind, these include;
    • Flywheel surface being too smooth which can cause shutter or slipping.
    • Incorrect flywheel step or recess ground; in the case where a flywheel is not flat the recess or step must be maintained. Failure to do this can cause engagement or disengagement issues.
  1. Risk of catastrophic failure; in situations where the flywheel is placed under extreme heat damage can occur to the steel microstructure weakening the flywheel which can lead to cracking or destruction of the flywheel.
  1. Decreasing the overall stack height. Modern actuation systems have limited bearing height adjustment so after 2-3 grinds the overall stack height of the clutch system can be reduced enough to cause disengagement issues.


Dual Mass Flywheels

Dual Mass Flywheels were introduced to dampen driveline vibration and noise more effectively. The need for this escalated due to increased torque in modern engines (especially diesel engines) and consumers expectations of noise and vibration.

A Dual Mass Flywheel (DMF) is comprised of two flywheels that work together with dampening springs or planetary gears to reduce noise and vibrations.

As the driveline dampening occurs in the flywheel most DMF clutch discs do not contain springs but are generally cushioned to give smooth engagement.

Although DMF’s are very effective at dampening driveline noise and vibration they have 4 major downfalls.

  1. Cost: the cost of a replacement DMF can be many times more than the cost of the clutch.
  2. Durability: due to the added complexity is it common that the DMF will fail before the clutch is fully worn.
  3. Unable to grind it is not generally recommended to grind a DMF meaning that in most cases the DMF must be replaced when the clutch is replaced.
  4. Poor heat sink: as a DMF is not a solid piece of steel it’s a poor heat sink to remove heat from the clutch disc.


Dual Mass Flywheel Replacements/Conversions

Dual Mass Flywheel Replacements (DMR) move the damping system from the flywheel to the clutch disc/plate. This returns the flywheel back to a conventional solid mass flywheel and the driveline dampening to the clutch disc.

To effectively dampen driveline noise and vibrations a multi rate (MR) clutch disc is used in DMF conversion kits (DMR). This MR clutch disc uses a torsional damper with separated first and second stage dampers. The dampener is tuned for low torque low angularity dampening as well has high toque, high angularity dampening.

Advantages Over a DMF

  • Increased ability to handle higher torque
  • Greater reliability
  • Better thermal dynamics
  • Cost efficient: Both on the initial purchase and ongoing with the ability to machine the flywheel

Note: as dual mass replacement/conversion (DMR) clutch kits do not as effectively dampen driveline noise or vibration an increased vibration and noise might be detectable especially at low RPMs. However, this will not damage the vehicle’s driveline.