Dual Mass Flywheels

The first dual mass flywheels that most New Zealand technicians were initially exposed to were fitted to Asian sourced (mostly diesel-powered) 4x4 vehicles. This variation on the dual mass flywheel theme was fitted with an internal clutch mechanism.

The internal clutch on these early dual mass assemblies was designed to protect the vehicle driveline from potential damage. In the event that the vehicle operator was aggressive with the clutch action while applying high levels of engine torque, the flywheel clutch would slip. This controlled slippage was designed to reduce the incidence of shock being transferred to the drive train and potentially causing shock related drive drain damage.

An unfortunate side effect of this designed-in drive line weak point was the eventual failure of the flywheel’s internal clutch, which would begin to slip when the vehicle was placed in a normal heavy load situation.

Many repairers were subsequently caught out as a client would report the clutch on their SUV was slipping. The unwary repairer would quote out the job and replace the clutch in the normal manner.

With the vehicle reassembled the repairers were less than impressed to find the clutch still “slipping”. The clutch supplier was then contacted, and after some often unpleasant words were exchange, the cause of the “slipping clutch” was correctly diagnosed.

The frustrated repairer would again dismantle the vehicle and replace the errant flywheel assembly..

For reasons of cost and perceived reliability the replacement flywheel was often a “solid” unit sans the internal clutch.

Perhaps it is these negative experiences that have tainted the repair industry against dual mass flywheels?

A number of factors have attributed to the demise of this internally clutched dual mass flywheel.

Principally the modern engine control systems limit the torque an operator can malevolently deliver to the drive line.

An earlier refinement has fluid dampers placed in the clutch hydraulic actuation circuit to limit the speed at which a clutch can be engaged.

With fewer requirements to protect the dive line from extreme engine toque shocks the more modern and now far more common format of dual mass flywheel has no internal clutch.

There are a number of different designs available, but most will utilise a set of radially located springs. These spring/damper assemblies are designed to dampen torsional vibration while controlling shock loads to the vehicle drive line.

So why are manufacturers fitting dual mass flywheels to modern vehicles?

The operators of modern passenger and commercial vehicles are demanding greater refinement, efficiency and performance from their vehicles.

Pursuing these goals has prompted the engineers to turn towards technologies that increase an engine’s ability to produce increased torque at low engine revolutions.

These new-generation engines may be either diesel or petrol fuelled. They will potentially have forced induction, coupled with less displaced volume and fewer cylinders than we are used to working with.

A popular example of a modern high efficiency engine is Ford’s multi award winning three-cylinder Ecoboost “Fox” engine as currently available locally in the Fiesta sport.

This three-cylinder configuration means there is a cylinder firing and resultant power pulse every 240 degrees of crankshaft revolution.

These 240 degree power impulses cause the speed of the engine’s rotating mass to pulse slightly.

If this engine was utilising a traditional single mass flywheel the torsional vibrations caused by the crank pulsing would require a very heavy flywheel and a heaver drive line. Both of these solutions would negatively impact on economy, while introducing a number of very complex power plant isolation challenges.

Enter the dual mass flywheel, by utilising as the name suggests two masses – one of the masses is bolted to the crankshaft, and the other has the clutch bolted to it. These two masses are coupled by a spring and damping medium.

Each dual mass flywheel is tuned to a particular application, and they are specifically designed and tuned to vibrate in the inverse to the crankshaft’s torsional vibrations.

These inverse vibrations have the effect of damping the crankshaft torsional vibrations that would otherwise be transmitted to transmission input shaft to virtually zero.

The net result of this dramatic reduction in transmitted torsional vibration is greater fuel economy, the transmission and drive train size can be reduced, and the client drives a more refined vehicle.

So here’s why you should retain the dual mass flywheel when replacing the clutch.

There are a number of opposing views around the Net on swapping out the dual mass flywheel for a replacement solid unit when replacing a worn clutch.

A less obvious advantage of the dual mass flywheel is the reduction of the clutch plate weight.

The lower rotating mass of the driven plate makes the transmission synchromesh job easier. The traditional sprung plate has a great deal more rotating inertial and will slow the gear change while accelerating wear on the synchromesh mechanisms.

If you choose to fit a solid clutch kit the following issues may occur.

Typically, the driver will notice an increase in engine vibrations and harshness. Perhaps the gear lever will emit an audible buzz at certain parts of the rev range: potentially the driver will notice an increased vibration from the lever while shifting gear.

Any warranty or goodwill claims that could be influenced by replacing the dual mass assembly would have a chance of being voided.

The high price of replacing a dual mass flywheel assembly has long been touted as the major driver for replacing the dual mass flywheel and clutch assembly with a traditional single mass flywheel and clutch.

The team at Ford has reacted to this information and has managed to position the genuine Ford replacement dual mass clutch and flywheel assemblies for its most popular vehicles in line with the cost of purchasing a quality single mass flywheel and clutch kit from a second tier parts supplier.

When you are next confronted with a clutch replacement on a Ranger or a Transit, price the parts for the job with your local Ford dealer. You could well be pleasantly surprised. You stand to get your parts at a good price while grabbing a load of Get Genuine reward points.

The security of knowing that your client is going to have a vehicle that performs exactly as the manufacturer intended, free from any extra rattles, vibrations and potential driveline issues that substituting a single mass assembly may introduce.