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High up on the list of repairs certain to strike fear into the heart's of car owners, is clutch problems. Most modern clutches are complex pieces of equipment and can be expensive to buy. In many cases buying a cheap replacement clutch from a breakers yard and fitting it yourself, with advice and guidance from your mechanic if needed, is the most cost effective solution.

What is the clutch/what does it do?

The clutch is a crucial part of the engine in a modern car with a manual transmission.  It is basically the starting point of transmission in a car with a manual gearbox. The clutch is a mechanical device which effectively allows the driver to regulate the engine's power to the gearbox, which enables the car to start and to move. Clutches serve this essential purpose by actively engaging and disengaging the power transmission system from the drive shaft.  The clutch works by adjusting the friction between the spinning engine and stationary wheels, enabling the driver to start the car without the car jerking; when moving, to change gear with ease; and to stop the car smoothly, without damaging the engine.

Getting into the details of the clutch

The clutch is situated between the engine and the gearbox, usually fixed directly to the front of the engine's flywheel, and the other side mounted to the manual transmission, which allows the crucial process of disengaging it to change gear. The clutch consists of four main parts: a clutch plate, which is attached to the flywheel; a pressure plate, which is fixed to the clutch plate; a diaphragm spring, which pushes the pressure plate against the clutch disc, which in turn pushes against the flywheel, and a throwout bearing, which applies pressure to the centre of the diaphragm spring. The clutch plate and the pressure plate are essentially two discs which can be moved apart or together by the clutch pedal and clutch lever. The clutch is connected to the clutch pedal (the far left foot pedal in the car) by a cable or, less commonly, a hydraulic piston. When the driver presses the clutch pedal down it moves the two plates apart. This disconnects the engine from the wheels which enables the driver to change gear. When the driver gradually raises the clutch pedal, this slowly moves the two discs together, which pushes against the flywheel, which reconnects the engine with the drive wheels. When the driver starts the car, the pressure plate is stationary, and the clutch plate, which is attached to the flywheel, and nearest to the engine, is rotating at speed. By gradually moving the discs together, with the action of releasing the clutch pedal, the friction slowly and evenly speeds up the stationary disc to match the rotational speed of the engine.

Fundamentally, the main function of the clutch is to allow greater control of the vehicle's speed, enabling the driver to start the car with ease, change gear smoothly and safely, as well as preventing the car from stalling when slowing to a stop.  In an automatic transmission there is an automatic clutch which cleverly operates in the same way that raising the clutch pedal in a manual transmission does.

What if something goes wrong with the clutch?

Understandably the clutch is critical for the car, and older or worn clutches can display a variety of symptoms, such as crunching or shrieking noises; a burning smell; difficulties when changing gear or excessive slippage when driving up inclines in a low gear. Just a few of the potential causes can include misalignment, worn input shafts or defective release bearings. Because this part operates with friction, it understandably warps and wears down over time with continued use. Sensible driving and careful and proper use of the clutch when changing gear will extend its working life and ensure this part doesn't wear as quickly, while helping it to function as effectively and efficiently as possible.

To work properly, the clutch has to have the correct amount of movement in the linkage between the foot pedal and the clutch lever. Restricted movement can lead to the clutch slipping, which happens because the pressure plate is unable to use its full power to put pressure on the clutch plate. If ignored, this can cause the clutch plate to burn out and potentially cause irreparable damage to the pressure plate. On the other hand, if there is too much movement between the linkage and foot pedal, this can cause the clutch to drag which makes the car difficult to get into gear and can cause the car to crawl forward when in gear with the clutch pedal pressed down fully. This can be a big problem for drivers on roads with heavy, congested traffic and can, if ignored, cause damage to essential components. Advice on the precise amount of movement required in the linkage can be found in the car's or manufacturer's manual or sought from your mechanic. The linkage should be checked and, when required, adjusted around about every 6,000 miles. Wear on the friction plate and on the linkage will eventually cause big damage to the car's transmission.

If the clutch doesn't feel right, or the transmission doesn't change smoothly as it should, there is a problem with the clutch and it's advisable to get it looked at by a mechanic. Whatever the case, when clutch problems strike it is critical for your own safety to have a replacement clutch ordered and fitted as soon as possible.