The What’s and How’s of Car Clutches

Since most cars in Australia come with an automatic transmission, relatively few drivers know what a clutch is or how it works. Clutches are the physical link between the engine and transmission. They come in different forms, but all with the same purpose – to transfer power from one component to another.  

What a Clutch Does

Clutches take the rotating force or torque produced by the engine, connect it to the drive shaft, and from here to the wheels. Since the engine is constantly spinning, there must be some way to break or discontinue that link, so the wheels and vehicle can safely stop. 

This is where the clutch pedal comes into the picture. When pressed, the clutch disengages the link between the engine and transmission is severed, allowing the driver to change gears up or down. Releasing the pedal reconnects the engine and gearing, and the power transfers to the wheels again. A torque converter does the same role in cars equipped with automatic transmissions.  

Clutches, in general, may be moving towards obsolescence, but for many, they’re the primary part that allows for a bit of driving fun. Many car brands bring back manual transmissions in at least one model trim in their higher-end sports cars. And while autos have become so technologically advanced, allowing for better efficiency and quicker gear changes, they can’t replicate the connection between driver and vehicle as a manual does. 

How a Car Clutch Works

These components are necessary for devices that transfer power using two shafts. One shaft is driven by an engine or pulley, while the other’s role is to drive another device. The clutch connects the two. It enables the shafts to be disconnected and spin at various speeds or locked together and spin at the same rate.

In cars, the engine spins constantly. So, if the engine was directly connected to the transmission with a single, continuous part, stopping would be impossible without inflicting damage or requiring to turn the engine off. However, the clutch allows the gearbox and engine to engage and disengage while controlling the friction between the two parts. 

It may sound complicated, but it’s really a simple design with three essential parts. One of these connects to the engine and another to the gearbox. In between is a friction plate that transmits torque between the two. 

The flywheel is the part bolted to the engine crankshaft and spins at engine speeds. The flywheel and disc press together when the clutch is engaged, enabling a smooth transfer of power from the engine to the transmission.

The pressure plate pushes the disc against the flywheel. A diaphragm spring or cover assists in this. It consists of sprung metal fingers facing inwards and provides the required clamping force to keep the plate and flywheel connected and prevent slippage. When the auto clutch is disengaged and the pedal depressed, an arm pushes a release bearing against the center of the diaphragm spring, which releases the clamping pressure.  

The Different Types of Car Clutches

There are different types of car clutches available. The setup described above is the single-plate friction type found in most cars. However, vehicles with more power can use a multi-plate variant with several friction plates stacked together, thus increasing the exerted friction and allowing higher torque output. The assembly is no larger than a single plate clutch but maximizes efficiency and, at the same time, prevents potential damage.  

Clutches can be further divided into dry and wet. Wet types use oil to keep them cool and lubricate the components. They also mostly have a multi-plate design and are found in performance vehicles. Dry types forego lubrication (which can cause them to slip) and are usually single-plate.  

While most types use hydraulics or cables, there are also electromagnetic or power-assisted options. These use a coil and electromagnetism to engage and disengage. You’ll often find them in cars with paddle shifters.

Lastly, dual-clutch transmissions are a newer electromagnetic type consisting of a small clutch for even gears and a larger one for odd gears. This means one is always engaged, allowing for crisp shifting to maximize engine performance.  

Can Car Clutches Fail?

Most factory car clutches will outlast the quoted warranties, meaning most will be good for 100 thousand kilometers or more. But this all depends on how you drive. 

Changing gears at unreasonable RPMs, lugging the car in high gear, low speeds, and hard starts with the engine revving are just a few driver habits that will wear down parts quicker than expected. 

Worn plates can lead to slipping, gradual or instant loss of power, the car holding onto unusually high RPMs, and difficulty changing gears. This can be accompanied by grinding noises, burning smells, and a soft pedal feel.  

While replacement parts and kits are easy to find, costs depend on the type. OEM clutches are direct replacements for a worn factory model and bring the same or similar performance. Look to the aftermarket if you need more.

The Right Clutch Option for Your Car 

OEM models are designed to work with the power the engine provides. Increasing torque and horsepower through tuning puts additional friction, and components will start to wear down more quickly. This is when to start looking for aftermarket auto clutches rated for the power numbers the engine puts out with the changes. 

Performance variants can better transfer torque and can cope with higher demands. Keep in mind that although there might be changes to the pedal feel and general drivability, it’s a price to pay for the additional performance.  

Single plate models can be updated with better materials in the friction plates, moving from the organic materials in OEM plates to carbon or Kevlar in uprated designs. The latter also has better heat dissipation and increased clamping. Ceramic components in automotive clutches are even better but prohibitively expensive and only seen in racing applications.  

While not uncommon to upgrade from a single to a multi-plate clutch, other parts may need to be changed. Lighter flywheels mean less moving mass, which is beneficial for reaching higher RPMs and aids with quicker gear changes. You’ll also need an uprated release bearing if you want faster actuation. Look for packaged kits with flywheels, bearings, friction plates, and cover assemblies from reputed parts suppliers.