How Does a Car Clutch Work? - FixMyCar

The clutch helps to get your car moving and allows you to change gears smoothly. It’s a complex part that experiences a lot of strain and sometimes needs replacing—but how exactly does it work? Find out in this guide.

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What does the clutch in a car do?

It isn’t just cars that have a clutch—many devices that feature two rotating shafts, including cordless drills and chain saws, rely on clutch systems. The clutch connects these shafts, locking them together so they spin at the same speed or decoupling them to spin at different speeds. 

In cars, the clutch connects the shaft from the engine to the shafts that turn the wheels. When you push the pedal, it disengages them, allowing you to change gear.

How does a clutch work?

Let’s take a look at that process in a little more detail. 

• When you press the clutch pedal, a hydraulic piston or cable pushes the release fork.

• The release fork presses the release bearing against the centre of the diaphragm spring, releasing the clamping pressure.

• The outer part of the pressure plate stops clamping the driven plate to the flywheel.

• The transmission of power to the wheels is interrupted, allowing you to change gears.

• When you take your foot off the clutch pedal, the thrust bearing is withdrawn, and the diaphragm-spring load clamps the driven plate to the flywheel.

• The transmission of power is resumed.

In a hydraulically operated clutch, pressure on the pedal activates a piston in the master cylinder, transferring power through a fluid-filled pipe to a slave cylinder, usually attached to the clutch housing. The slave cylinder piston is connected to the release arm.

Glossary

Since you might be unfamiliar with several clutch-related words, we’ve compiled this handy glossary.

Transmission

The transmission transfers power from the engine to the wheels and is usually mounted to the frame of a vehicle at the front. The term is often used interchangeably with gearbox, although not all transmissions have gears. The gearbox, if a car has one, is part of the transmission system.

Flywheel

The flywheel stores rotational energy and transfers it between the engine and transmission. This guide explains flywheels in more detail.

Clutch plate

The clutch plate is a disc with high-friction material around the perimeter on both sides. One side acts against the face of the flywheel, and the other acts on the pressure plate.

Pressure plate

This plate applies pressure to the clutch plate when the transmission is engaged, transferring torque to keep the car moving. It is bolted to the flywheel, so it spins at the same time and speed. The clutch plate sits between it and the flywheel but isn’t connected to the pressure plate.

Clutch plate springs

Springs are mounted on the inner hub of the clutch plate to cushion the clutch engagement. They absorb fluctuations in the engine’s power delivery to reduce vibrations.

Torque

Put simply, torque is the measurement of an engine’s rotational force. The more torque an engine has, the more power it can produce and the faster it can accelerate when the vehicle sets off.

Driven plate

The driven plate connects the flywheel and pressure plate to transfer power to the gearbox.

Diaphragm spring

One way to understand the diaphragm spring is to imagine your own diaphragm controlling your movement as you breathe. 

The spring is made of ‘fingers’ at the pressure plate’s centre. When you engage the clutch, these fingers force the pressure plate onto the clutch plate and the clutch plate onto the flywheel. The spring also acts as a release lever.

Release bearing

The job of the release bearing is to press against the diaphragm spring to disengage the clutch. It absorbs the rotary motion of the spring fingers.

Release fork

The release fork pushes the bearing into the diaphragm spring.

Splined hub

Splines at the end of the input shaft mate with the splines at the centre of the clutch plate. The input shaft then transfers the clutch's motion to the gearbox. When the clutch pedal is disengaged, the input shaft doesn’t spin; when the pedal is engaged, the shaft spins at the same RPM as the flywheel.

Under load

When someone refers to the load on a car, they mean the amount of torque applied to its engine. In a car that is ‘under load’, the engine has taken up the vehicle’s weight; the clutch pedal is not pressed down.

How do you use the clutch?

In manual cars, the clutch is engaged and disengaged using the clutch pedal, which means you need to learn how to use clutch control to find the biting point and set off with the right amount of acceleration.

How many clutch parts are there?

Five main parts combine to create the clutch plate:

• Driven plate

• Cover plate

• Pressure plate

• Diaphragm spring

• Release bearing

The flywheel and transmission are other important parts linked to the clutch system.

Different types of clutch systems

There are many different types of clutch systems. Some of the most common ones are discussed below.

Manual transmission clutch

As the name suggests, in a manual transmission vehicle, the driver must select the correct gear and use the clutch pedal to shift manually. There are also different types of manual systems.

Dual-clutch

A dual-clutch transmission uses two clutches, which can be wet or dry. Typically, one clutch operates the even gears (two, four and six), and the other operates the odd gears (one, three, five and reverse).

Dual-clutch systems are often found in modern racing cars and are common in older vehicles. Today, dual-clutch manual transmissions are usually automated, relying on a computer to control clutch engagement and shifting gears, which bridges the gap between manual and automatic systems.

Synchronised/constant mesh

This type of transmission keeps the cluster gear, mainshaft gears and drive gear constantly moving, using pads to slow the gears down.

Unsynchronised

Early manual transmissions were unsynchronised and often nicknamed ‘rock crushers’ because drivers would grind the gears together while attempting to get them to mesh. These transmissions were standard in lorries until the early s.

Automated

An automated manual transmission (AMT), also known as a semi-automatic, is a conventional manual system that also features a computer to operate the clutch and shift gears automatically. 

Automatic transmission

Automatic transmissions don’t usually use clutches; they rely on torque converters. They can have different types of gearboxes, such as:

• Direct-shift

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• Hydraulic

• Tiptronic

Learn more about how automatic transmissions work.

Wet vs dry clutches

Wet clutches use a multi-plate design and are covered in oil, which allows the clutch plates to cool more quickly. As a result, they often last longer and are less noisy when idling. This clutch type is favoured by vehicles with higher torque.

On the other hand, a dry clutch features a single-plate design and is not lubricated with oil. Some argue that this makes dry clutches more dependable for performance because liquid can create losses of power from the drivetrain (a group of parts that work with the engine to move the wheels, including the transmission).

Most cars with an automatic transmission have a wet clutch, while many manual cars have a dry clutch.

Signs your clutch is going

Common signs of clutch failure include:

• Slipping out of gear

• Grinding noises

• Unusual clutch pedal behaviour

• Poor acceleration

This guide discusses how to tell if you need a new clutch for your car in more depth.

FAQs

Do electric cars have a clutch?

Electric cars are automatic, so they don’t have a clutch. Find out whether EVs are easy to maintain.

Where is the clutch in a car?

The clutch is between the engine, flywheel and transmission.

What comes in a clutch kit?

A clutch kit contains various parts to replace or upgrade a clutch. Most kits include a pressure plate, clutch disc, flywheel and release bearings and may also come with an alignment tool. You can buy kits for all vehicle types, from hatchbacks to sports cars. This guide explains what happens when your clutch is replaced.

Are you experiencing problems with your clutch? Whether you need a repair or replacement, FixMyCar can help you find the right garage at the right price.

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