Clutch: general information and design (BMW 3 Series E36)

The clutch in a car performs 2 tasks: When changing gears, it interrupts the transmission of torque from the engine to the gearbox, and when starting off, its friction ensures the transmission of torque without jerks.

The clutch consists of a driving disc, a driven disc and a release bearing.

The leading clutch disc is rigidly fixed to the flywheel, which in turn is fixed to the flange of the engine crankshaft. Between the leading disc and the flywheel is the driven clutch disc, which is pressed by the leading disc to the flywheel. The driven disc is centered by the primary shaft of the gearbox, which is in toothed engagement with it.

When the clutch pedal is pressed, the release bearing is pressed against the springs of the clutch drive disc via the hydraulic drive and the release lever. As a result, the clutch drive disc is released and the driven disc is no longer pressed against the flywheel. The transmission of torque from the engine to the gearbox is interrupted.

All models are equipped with a hydraulic clutch drive: The piston of the hydraulic system's slave cylinder is located near the release lever. When the clutch pedal is pressed, the movement of the master cylinder piston creates pressure, which is transmitted through the pipeline to the clutch slave cylinder, which is secured with a flange on the gearbox. The piston of the slave cylinder exerts pressure through the clutch fork on the release bearing and, overcoming the force of the diaphragm springs of the drive disk, slightly moves it away.



The hydraulic clutch drive operates on brake fluid and is supplied with it from a reservoir shared with the brake system.

When the clutch pedal is released, the driven disk is pressed by the driving disk against the flywheel under the force of the diaphragm springs, creating a transmission of torque from the crankshaft to the input shaft of the gearbox.

Each time the clutch is engaged and disengaged, the working surface of the driven disk wears out due to friction during slippage. Thus, the driven disk is subject to wear and has an average service life of about 100,000 km. Wear depends primarily on the load (trailer operation) and the driver's driving style. The clutch does not require maintenance, as it is self-adjusting.