Dual Mass Flywheels
A dual mass flywheel contains two plates, a bearing, and internal springs that absorb torsional vibrations. Today's diesel and powerful four-cylinder engines create a substantial power stroke. A dual mass flywheel significantly reduces these engine pulses and driveline vibrations before they enter the drivetrain.
The internal springs weaken and break, causing the excessive movement; this causes the secondary plate to oscillate, resulting in noise and driveline vibration. The severity depends on how bad the flywheel is; if it's just beginning to fail, there may be a rattling sound at cruise. The pitch changes as the clutch is engaged and disengaged. When completely worn, they will make a loud rattling noise, usually noticeable right at startup.
Dual Mass Flywheel Diagnosis
A new dual mass flywheel has a little movement between the plates; internal springs absorb the side-to-side movement. As the springs wear, this play increases. Read the manufacturer's specifications before proceeding, typically if the left to right play is more than an inch, replace the flywheel. Most shops replace these flywheels with every clutch job.
Lots of vehicles have dual mass flywheels, but they are expensive. They reduce torsional vibrations, primarily when the clutch first engages. Diesel engines and today's turbocharged four-cylinder engines benefit from these flywheels. The transmission must be separated from the engine to replace the flywheel.