The dual-mass flywheel does a good job of reducing neutral gear rattle and improving manual transmission shift quality in performance cars. It may even be more important in heavy-duty truck diesels, where it suppresses the larger torsional spikes that can damage transmission gear teeth. In either case, when the dual-mass flywheel requires replacement, the cost becomes an issue, particularly if the clutch also has worn out.
A solid flywheel is an alternative but is by itself an impractical one, primarily because the driver will be dissatisfied with the vibration and poorer shift quality, and transmission life will be affected. Valeo Transmissions, which is a manufacturer of replacement dual-mass flywheels, is recommending conversion kits as a lower-cost alternative, in which a clutch driven disc with sophisticated damping features performs much of the function of the dual-mass flywheel. The solid flywheel and clutch disc are an engineering-matched set.
The Valeo kits were introduced in Europe, where they have been available for Volkswagen, Audi, and BMW cars, with a Mini Cooper S kit to come. In addition, kits were released for Hyundai vehicles plus the Kia Optima. Now the line is being sold in the U.S., and there also are kits for the heavy-duty (turbocharged diesel-equipped) versions of Dodge Ram (Cummins 5.9- and new 6.7-L sixes) and Ford F series (7.3-L V8 through to 1998), and 1992-95 Chevrolet/GMC 6.5-L V8 (with a DuraMax 6.6-L V8 kit to come).
In the Valeo kits, the driven disc has a "floating" hub assembly with coil-in-coil springs for the main damping and a four-coil spring "cassette" as a pre-damper. The truck engine disc hub design allows up to a class-leading 40º of relative movement between the outer (spring retainer) plates and the center (transmission shaft) plate to compress the springs to control vibration. Less-demanding conventional designs may have only 20º or less of relative movement.
Called a Long Travel Damper, the Valeo design has curved springs for the coil-in-coil, which permit increased travel for a given torque. The use of inner coil springs permits increasing the main damper torque capacity as required. The pre-damper, which provides the primary control at idle speeds, and the main damper work in series. The main damper coil wire is a high-strength oval cross section, which is rated for the longer travel.
Dual-mass flywheels are engineered to be durable and are tuned to dampen when the rpm is outside the engine's optimum range, during which most torsional vibration is produced. However, the intervals of vibration grow longer as an engine ages, when internal moving parts wear, fuel injectors perform with less precision, engine mounts deteriorate, etc. This increases the amount of damping operation that must be performed by the dual-mass flywheel, shortening its service life.