What Are Dual Mass Flywheels And Why Do They Cause So Many Problems?

Dual mass flywheels (DMFs) are used on standard manual transmissions to reduce the torsional vibrations that occur when shifting. Without the DMF, there was a higher chance of long-term damage due to excessive vehicle vibration. Over time, luxury, high-performance UK vehicles started putting dual mass flywheels in their clutches to improve ease of shifting.

Benefits of the DMF

The DMFs are used to improve performance, as well as reduce harmful torsional vibration in the gearbox, driveline and transmission by distributing the vibration from the clutch disc to the engine flywheel. In light diesel trucks, the transmission has higher compression ratios and is more sensitive to torsional inputs. DMFs were a welcome solution because they prevented damage to the transmission gear teeth.

With higher petrol prices, fuel economy savings are more important. Dual mass flywheels permit lower idling rpms, which leads to less fuel being needed. The dual mass flywheel clutch disc handles the engaging/disengaging functions. The DMF eliminates excessive transmission gear rattle, making it easier to shift, especially from first to second gears.

The conventional single flywheel was split into two with one flywheel controlling engine inertia and the other flywheel controlling transmission inertia. The DMF has a primary and secondary flywheel with torsion springs, cushions, clutch disc and a center support. The center support bearing carries the load between the inner and outer flywheel.

The damper friction ring is the link between the flywheels. It allows the inner and outer flywheel to slip to distribute pressure more evenly to dampen torsion vibrations and absorb shocks. Unfortunately, this is the weakest link so it can wear out quickly.

There is a high failure rate for DMFs, so some automobile and truck manufacturers are replacing these with a single solid flywheel or engine control unit (ECU) software.