The first stage in the
of a car with a manual gearbox is the
power to the
box, and allows transmission to be interrupted while a gear is selected to move off from a stationary position, or when gears are changed while the car is moving.
Most cars use a
clutch operated either by fluid (
) or, more commonly, by a cable.
When a car is moving under power, the clutch is engaged. A
bolted to the
, by means of a
spring, on the driven
Earlier cars have a series of
at the back of the
plate, instead of a diaphragm spring.
The driven (or friction) plate runs on a splined
, through which the power is transmitted to the gearbox. The plate has friction linings, similar to
linings, on both its faces. This allows the drive to be taken up smoothly when the clutch is engaged.
When the clutch is disengaged (pedal depressed), an arm pushes a release
against the centre of the diaphragm spring which releases the clamping pressure.
The outer part of the pressure plate, which has a large friction surface, then no longer clamps the driven plate to the flywheel, so the transmission of power is interrupted and gears can be changed.
When the clutch pedal is released, the
is withdrawn and the diaphragm-spring load once again clamps the driven plate to the flywheel to resume the transmission of power.
Some cars have a hydraulically operated clutch. Pressure on the clutch pedal inside the car activates a
, which transmits the pressure through a fluid-filled pipe to a
mounted on the
The slave-cylinder piston is connected to the clutch release arm.
Parts of the clutch
The modern clutch has four main components: the cover plate (which incorporates a diaphragm spring), the pressure plate, the driven plate, and the release bearing.
The cover plate is bolted to the flywheel, and the pressure plate exerts pressure on the driven plate through the diaphragm spring or through
springs on earlier cars.
The driven plate runs on a splined shaft between the pressure plate and flywheel.
It is faced on each side with a friction material which grips the pressure plate and flywheel when fully engaged, and can slip by a controlled amount when the clutch pedal is partially depressed, allowing the drive to be taken up smoothly.
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If your car has a cable-operated clutch and you find that the gears are
difficult to engage, the pedal action is stiff, or there is any sign that the
clutch pedal is reluctant to come back up again, then the chances are that the
clutch cable is damaged.