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Notes From the Road

How Clutches Work
By Mike Bumbeck/

Between the flywheel and the pressure plate is component number three, the clutch disc. The clutch disc has friction surfaces similar to a brake pad on both sides that make or break contact with the metal flywheel and pressure plate surfaces, allowing for smooth engagement and disengagement. The fourth and fifth components of the clutch assembly work together, and are the keys to this, at once, engaging and disengaging process. They are the release, or throw-out bearing, and the release system itself. The release bearing is connected to one end of the hydraulic, or clutch fork mechanism, and rides on the diaphragm spring of the clutch. Depending on the type of release system, the throw-out bearing either pulls or pushes on the pressure plate diaphragm spring to engage or disengage the pressure plate's grip on the clutch disc when the clutch pedal is depressed and released.

In the Clutches of Traffic
Running right through the center of the pressure plate, clutch disc, and flywheel is the input shaft of the transmission. The input shaft takes the input, or power of the engine, and sends it down through the gears to the wheels. At the point where the input shaft enters the transmission resides a beefy bearing that bears most of the shaft's spinning load. In the middle of the flywheel is much smaller pilot bearing. The pilot bearing centers the input shaft smack in the center of the flywheel so it can rotate while the clutch assembly is engaged and disengaged. It is the input shaft the clutch disc itself is connected to.

While the clutch is engaged, everything spins as one unit. When you press the clutch pedal in, the clutch assembly is disengaged. The shaft and clutch disc spin independently of the flywheel and pressure plate. As you let the clutch pedal out, the friction surfaces on both sides of the clutch disc begin to make contact with the metal surfaces of the flywheel and pressure plate, and the power of the engine is transferred through the transmission input shaft, through the gears, and right down onto the road. The tricky part is matching up the speed of the engine to the engagement of the friction surfaces so you don't get caught in the clutches of a potentially embarrassing engine stall.

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