Every car has a clutch and we all know that it is one of the most important car parts. After all, clutch control is the first thing we're taught as learners! But do you know exactly what the clutch does and why we should look after it as best we can?

By the end of this article, you will understand:

  • What the clutch does
  • How many clutch parts there are and their individual jobs
  • How the clutch and transmission work together
  • Some of the different types of clutch systems and how they differ
  • What to do if you notice a clutch problem

 

Glossary

Flywheel - A heavy disc attached to the end of a rotating shaft. It stores energy to smooth out the delivery of power from the engine to the transmission. It can also store energy through a process known as 'rotational momentum'. This can be used during acceleration to improve your car's fuel economy.

Transmission - Mounted directly on top of your engine, the transmission converts combustion power into energy that your car can use to move forward. Without the transmission system, your car wouldn't move anywhere.

Under Load - The load placed on a car refers to the amount of torque applied to its engine. A car that is "under load" simply means a car whose engine has taken up the full weight of the vehicle. 

Centrifugal - The force felt by an object moving in a curved path away from the centre of rotation. For example, a vehicle turning a corner would have centrifugal force exerted upon it.

Wet vs Dry Clutch Systems - Two different clutch systems. Wet clutches tend to have multiple clutch plates and need lubricating oil to keep the parts cool. Dry clutches generally only have one clutch plate and don't require oil to remain cool.

 

Summary

Your car's clutch allows you to speed up or slow down by disconnecting the engine from the wheels without switching it off. This is useful because the engine constantly spins, but the wheels don't. The clutch also works with your transmission to get your car moving in the first place. Due to the low amount of torque generated at low speeds, you can't start the engine with any load applied. That's why you need to book a clutch replacement as soon as you notice any warning signs of clutch failure.

The clutch system is made up of 5 main parts and works closely with the flywheel. Most cars use a single plate system, but some may use a multi-plate or other clutch system. The clutch works differently depending on what system and gearbox your car has.

 

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What Does the Clutch Do?

The clutch connects your car's two rotating shafts, allowing for three things.

  1. The shafts locking together so they spin at the same speed
  2. The shafts slipping by a controlled amount when the pedal is partially depressed
  3. Or decoupling the shafts altogether so they spin at different speeds.

This is handy because your engine spins all the time but the wheels don't. In order to speed up, slow down or stop without killing the engine, the two need to be disconnected.

Your clutch engages while your car is moving. This means that the pressure plate exerts constant force onto the driven plate through a diaphragm spring, locking it in place. When you depress the pedal, you disengage the clutch. An arm pushes the release bearing against the centre of the diaphragm spring, releasing the clamping pressure from the pressure plate. This stops the power from the engine from reaching the wheels, allowing you to change gear. Releasing the pedal re-engages the transmission. Then, the friction linings on the driven plate smoothly take up the drive again.

 

How Many Clutch Parts Are There?

There are 5 clutch parts that combine to form the clutch plate. The clutch also works closely with the transmission and the flywheel.

 

disassembled clutch system

From left to right: Cover Plate, Release Bearing, Pressure Plate and Driven Plate

 

Cover Plate

This metal housing is bolted to the flywheel, connecting it to the clutch assembly. It makes sure that engine torque transfers to the gear shaft through the clutch disc.

 

Driven Plate

Also known as the friction plate, this runs on a splined input shaft between the pressure plate and flywheel. It transmits power to the gearbox and has friction linings, just like brake pads. If these linings wear down too far, the clutch can slip and not reengage properly.

 

Pressure Plate

Also known as the clutch cover, this is a large ring that applies pressure to the clutch plate while the transmission is engaged. This allows your car to transfer torque to the transmission and keep you moving smoothly.

 

Diaphragm Springs

This is a large, round spring steel disc mounted in the clutch cover. The outer edge touches the back of the pressure plate and releases the clamping pressure when you depress the clutch pedal. As it does this, it disconnects the transmission from the wheels.

 

Release Bearing

Also known as the clutch bearing or throw-out bearing, this reduces friction between the pressure plate and the release fork. When the fork moves from side to side, the release bearing slides along the transmission sleeve.

 

How Do the Clutch and Transmission Work Together?

Your car's engine only produces a small amount of torque when stationary. This means you can't start the engine under load - hence why you need to depress the clutch pedal to start a manual car.

To transfer the engine's power through the transmission into the wheels, your car needs a system to gradually take up the load. This system is the clutch.

As you release the clutch, the transmission takes up the load and gets you moving smoothly.

 

A cross-section of clutch and transmission system from a car on a white background

A cross-section of the clutch and transmission assembly. The clutch plate is the first few rings on the left of the assembly, with the gearbox behind it. As you can see, the two work very closely together!

 

Does the Clutch Work Differently Depending on What Gearbox Your Car Has?

Yes, the clutch can work in different ways in different types of gearboxes.

For example, an automatic transmission has several clutches. They engage and disengage various sites of planetary gears and, because there is no clutch pedal, it's all controlled by the computer.

Other types of clutch system include:

  • Cone clutches
  • Centrifugal clutches
  • Wet vs Dry systems
  • Vacuum clutches
  • Electromagnetic clutches

Plenty of appliances use a clutch system. Smaller appliances, such as power drills, can't use a pedal and so require a different clutch system. These all work slightly differently as a result.

 

Single Plate Clutch vs Multi-Plate Clutch

Most cars use a single plate clutch system, but many motorcycles, race cars and HGVs use a multi-plate clutch system.

While a single plate system is the simplest way to change gear, a multi-plate system helps the clutch transmit more torque because it has more friction surfaces. This makes it more efficient for heavy vehicles and racing cars which need quicker gear changes at higher speeds. Plus, it is also smaller than a single-plate system, which makes it perfect for motorcycles.

The main differences between a single plate and multi-plate clutch are:

  • Number of clutch plates
  • Location of the plates. In a multi-plate system, the pressure plates are alternately fitted to the crank shaft and gearbox
  • A single plate is a dry system, while a multi-plate is wet

 

What Happens If I Have a Problem With My Clutch?

If you notice a problem with your clutch, you need a clutch replacement. Whether you complete this process yourself or book an appointment with a local garage, you must act soon to keep the repair cost as low as possible. Find out more about a clutch replacement, including what warning signs to look for, by clicking the link above. You can also book your appointment at a garage near you by entering your vehicle reg and postcode into our booking tool and comparing instant prices.