What Is a Clutch?

A clutch is found in manual vehicles and essentially controls the connection between the shaft coming from the engine and the shafts which turn the wheels so you can change gears.  Below is an overview of the components that make up your car's clutch.

The flywheel

The flywheel attaches directly to the crankshaft. All flywheels have three purposes, the first being to provide rotational mass to counter the force of compression during idling or low engine speeds, which is what allows an engine to idle. Its secondary purpose is to provide one of the solid surfaces between which the clutch, or driven plate is clamped when the clutch is engaged. Its third purpose is to accommodate a ring gear that engages with the starter motor in order for the starter motor to rotate the engine during cranking.

The clutch, or driven plate

The driven plate consists of a disc to which friction linings are attached, and a hub that while it is separate from the main disc, is supported by a series of springs. The primary function of the springs is to absorb some of the engine’s torque during initial clutch engagements to relieve some of the torsional stresses being imparted to the main disc and friction linings. In practice, the engine’s torque is transmitted to the main disc (and friction linings) by the springs, which allows a small (and limited) measure of differential rotation between the main disc and the hub to absorb shock loads to the clutch assembly during gear changes, and especially gear changes performed during aggressive driving.

The pressure plate

Also known as the clutch cover, the pressure plate consists of an outer shell that encloses a heavily spring-loaded diaphragm. In practice, the spring-loaded diaphragm is the component in the clutch assembly that provides the clamping force required to transmit the engine’s torque to the transmission.

When the driven plate is fitted between the flywheel and the pressure plate during a clutch installation, the spring-loaded diaphragm is compressed by an amount that is roughly equal to the driven plates’ thickness to provide a constant clamping force on the driven plate when the clutch is engaged. 

The release bearing

When the clutch pedal is depressed the release bearing acts on the inner part of the pressure plate diaphragm, which causes the diaphragm to lift away from the driven plate. This removes the diaphragm’s clamping force from the driven plate; in this position, the clutch is disengaged and the engine is decoupled from the transmission, thus making it possible to change gears.  

Under normal driving conditions, a typical clutch should last for at least 150 000km, but as with anything else, clutches do fail for a variety of reasons. 

If you have concerns about your clutch, you should consult a qualified professional.