Clutches are important in mechanisms that have two rotating shafts. One of the shafts is usually driven by a motor while the other shaft drives another device. In a drill, for example, one shaft is driven by a motor and the other drives a drill chuck. The clutch connects the two shafts so that they can either be locked together and spin at the same speed, or turn at different speeds.
Your car needs a clutch because the engine spins all the time, while it's wheels do not. For a car to stop without stalling and killing the engine, the wheels need to be disconnected from the engine somehow. The clutch permits the transmission (automatic or manual) to smoothly connect to a spinning engine by controlling the slippage between them. A clutch works based on friction, the measure of how hard it is to slide one object against another. Friction is caused by the high and low points that are part of every surface - even the smoothest of surfaces still have microscopic peaks and valleys. The bigger these peaks and valleys are, the more friction is created when something slides against the object.
In your car's clutch, the flywheel is connected to the engine, while the clutch plate is connected to the transmission. When the pedal is not depressed by the driver's foot, springs push the pressure plate against the clutch disc, which in turn presses against the flywheel. This make a connection between the engine and the transmission input shaft, allowing them to turn at the same speed.
How much force the clutch can pass on from the engine to the transmission depends on the friction between the clutch plate and the flywheel, and how much force the spring puts on the pressure plate to press it against the clutch. When you press down on the clutch pedal with your foot, a cable or hydraulic piston pushes on the release fork that then presses the throw-out bearing against the center of the diaphragm spring. As the center of the diaphragm spring is depressed, pins near the outside of the spring cause it to pull the pressure plate away from the clutch disc. This seperates the clutch from the spinning engine. Until the 1970s, drivers could expext between 50,000 and 70,000 miles from a clutch. Modern clutches can last for 80,000 miles or more if they are used gently and well maintained. Without proper care, clutches can start to break down in as little 35,000 miles.
The most common issue with clutches is when the disc's friction material wears down. The friction material on a clutch disc is much like to the friction material on the pads of a disc brake or the shoes of a drum brake, and eventually, it wears away. When most of the friction material has worn off, the clutch will start to slip, and sooner or later will no longer transmit any power from the engine to the wheels.
Golden State Transmission and Muffler 10792 Olson Dr., Rancho Cordova, California 95670 916.853.1788