Dual-Mass Flywheel
A flywheel split into two halves connected by a spring damping system, designed to reduce drivetrain vibrations in manual transmissions.
A dual-mass flywheel (DMF) is a specialized engine flywheel designed for vehicles with manual transmissions, particularly diesel engines and high-torque turbocharged vehicles. Unlike a traditional solid steel flywheel, a DMF is split into two sections: a primary mass bolted to the engine crankshaft, and a secondary mass bolted to the clutch assembly. The two halves are connected by internal dampening springs and friction discs.
The primary function of a DMF is to isolate the torsional vibrations generated by the engine's power strokes, preventing them from transferring into the transmission gearbox. This reduces gear rattle noise, protects the transmission syncros from stress, and makes shifting smoother and more comfortable for the driver.
Over time, the internal springs and bearings of a DMF can wear out, fatigue, or break, especially under aggressive driving or vehicle overloading. Symptoms of a failing DMF include a loud rattling or clunking noise from the bellhousing (particularly at idle or shut-down), excessive clutch pedal vibration, and clutch slippage. Because a worn DMF cannot be resurfaced like a solid flywheel, it must be replaced during a clutch service.