# Dual mass flywheel description

From late 5/86 production, a dual mass flywheel was added to the 2.7 Liter ETA engined vehicles with manual transmission.

A dual mass flywheel's primary function is to reduce body drumming ( resonant vibrations ) and rattling in the transmission (torsional irregularities as the drive-line rotates).

Depending on speed range, the application of the dual mass flywheel improves noise levels inside the car by 2 to 8 dBA. It also increases low end torque due to weight, but requires more energy for the engine to turn, so suffers slightly slower reaction to the throttle.

The spring dampeners previously located in the clutch plate itself have been moved to the flywheel. This lowers the inertia of the clutch plate and also allows easier shifting.

Also aiding easier shifting, especially at low ambient temperatures, is the use of ATF instead of gear oil. The lower transmission noise level with the dual mass flywheel allows the use of ATF as a lubricant without increasing the noise level inside the vehicle.

The dual mass flywheel consists chiefly of primary mass with the starter ring gear, a spring damper system and the secondary mass which is the contact surface for the clutch plate. The primary flywheel mass is mounted to the crankshaft.

A multiple stage damper with three spring groups and the external damper is contained in the spring damper system. Each damper assembly consists of spring guide plates, springs and centering flange , including the friction elements in the form of spring washers and friction liners.

The secondary flywheel mass is guided on the primary mass with a sealed and heat insulated bearing. Rivets are used as connectors between the primary or secondary flywheel mass and the spring damper system.

### Operation description

At idle speed the first stage damper springs act together with the friction elements (diaphragm springs and insulating caps) between the primary flywheel mass and bearing at idle speed.

During normal driving , stages two and three of the driving damper as well as the friction elements are engaged in the complete driving range depending on the engine's load condition.

During starting and stopping, the critical resonance speed will be reached at approximately 400 rpm. This will produce large relative movement between the primary and secondary flywheel masses, for which all friction elements especially the external damper, will be actuated to dampen the resonance.

With the dual mass flywheel , it is possible to use driving ranges with very low speeds, which can have a positive effect on emissions and fuel consumption.

E30 M3 Repair Manual V2.7. Copyright ©1999-2001 Koala Motorsport & Brett Anderson