Replacing Your Clutch
Three things to consider
Abby Wingett | 3rd June 2022| 14 minutes to read
When it comes time to replace the clutch in your vehicle, it's important to make sure you have a good understanding of how the system works, the parts that make up the clutch assembly or kit and how to pick out the best type of clutch to suit your unique preferences, driving style and vehicle type. In a market teeming with options and obscure part numbers, it's easy to become overwhelmed and pass off the task to a mechanic, however with just some basic know-how and a good understanding of all the lingo, you can pick out your own clutch and even get to fitting it yourself if you're handy on the tools.
1. What is a clutch and how does it work?
Your clutch provides a mechanical connection between the engine and the rest of the driveline, allowing power from the engine to be sent through the gearbox and to the wheels which drive the car. When the clutch pedal is depressed, an arm (clutch fork) presses on a release bearing which releases the clamping pressure and the mechanical connection is broken. In this interruption of power through the gearbox, higher or lower gears can be selected or the vehicle can remain at a stand-still without stalling.
Your clutch system contains a few parts which allow for smooth engagement, reliable operation and the ability to deal with a variety of applications and driving styles. While the main parts are the clutch plate and pressure plate, there are several other often overlooked pieces which can be a make or break when it comes to installing your new clutch kit.
Clutch components explained:
- Clutch Cover - A spring-loaded diaphragm which clamps the friction plate to the flywheel. Varying levels of spring tension between different models of clutch allow for higher clamping forces, higher torque capability, higher power resistance and more aggressive pedal feel.
- Friction Plate - The link between the engine and the transmission. It's surface area and material type vary in accordance with the power and torque levels associated with the clutch kit. This piece also features springs which dampen engagement forces, however with higher end clutches designed for excessive power and aggressive driving, these springs become more aggressive or even non-existent. Some clutches feature twin or triple plate arrangements which use two (often smaller diameter) friction plates for extremely high torque ratings and compatibility with seriously high performing engines.
- Flywheel - The flywheel is connected directly to the engine's crankshaft. The flywheel acts a mounting surface for the clutch cover and also acts as a ring gear for engagement with the start motor. The flywheel also helps to maintain rotating mass during driving which makes for smoother gear shifts and more comfortable driving. High performance vehicles may call for light weight flywheels which can help to increase engine performance by decreasing the engine's rotating mass. Some vehicles use a DMF (dual mass flywheel) to dampen engine and driveline vibrations. Unlike standard flywheels, DMFs cannot be re-surfaced when replacing the clutch which means a new DMF must be fitted. There is also the option to fit a DMR (dual mass replacement), a conversion kit to replace the dual mass flywheel with a solid unit.
- Pilot Bearing (also referred to as spigot bearing, spigot bush or pilot bush) - Not a necessary component in all applications, most commonly found on rear-wheel drive layouts. The job of the pilot bearing is to support the engine-side of the gearbox input shaft. The bearing is located in the back of the crankshaft or the centre of the flywheel and helps to locate the input shaft when the clutch is disengaged.
- Clutch Release Bearing (also referred to as a throw out bearing) - This is attached to the clutch fork and presses against the clutch cover's spring diaphragm in order to release the clutch. While pressing on the clutch cover, the release bearing spins to match the speed to the engine / clutch assembly.
- Concentric Slave Cylinder - Only applicable to certain vehicles, a concentric slave cylinder is effectively a combo of a release bearing and a slave cylinder. A concentric slave cylinder does away with the need for a clutch fork and instead hydraulic pressure is sent directly to the concentric slave cylinder which presses on the clutch cover to release the clutch.
- Clutch Fork - This arm is connected to the gearbox and is actuated by the clutch slave cylinder. The slave cylinder presses on the clutch fork which presses on the clutch cover using the release bearing previously mentioned to disengage the clutch.
- Master Cylinder - This is one of the two main parts of the hydraulic system in the clutch. The clutch master cylinder is attached to your clutch pedal and transfers pedal action into hydraulic pressure which is then sent via the clutch line to the slave cylinder.
- Slave Cylinder - The clutch slave cylinder receives input from the master cylinder at the other end of the clutch line. When the slave cylinder is actuated, it uses a piston to push the clutch fork / release bearing assembly to disengage the clutch.
2. Do I need to machine my flywheel when I change my clutch?
When a new clutch kit is installed the flywheel must be either replaced or machined. This is because excessive heat from normal driving changes the structure of your flywheel surface, offering less friction which noticeably affects the performance of a new clutch. By replacing or machining your flywheel, the surface is reinstated back to the original equipment friction characteristic and is ready to receive the new clutch.
Advantages of flywheel replacement over machining:
- Reduced risk of catastrophic failure due to fractures in the flywheel - Over time due to heat, the flywheel microstructure develops cracks and heat spots which weaken the overall strength. With flywheels spinning at thousands of RPMs, it's important that this piece is structurally sound.
- Retains original thickness, ensuring correct engagement and disengagement - When machining a flywheel, the overall height decreases which can cause the clutch to not fully engage, reducing clamping pressure and torque capacity.
- Reduced installation time - On average 4.5 hours are lost waiting for the flywheel to be machined, this is time that you could be spending getting your new clutch kit installed on the car.
3. How to choose the right clutch for your car?
Now that you know how the clutch works and all the parts that go into the system, it's time to figure out what type of clutch is best suited to your unique application, driving style and vehicle requirements. Whether you need to replace the clutch in your eco hatch-back daily driver, fully built 1000HP racecar or anything in between, there's a clutch at Repco for you.
OE-Spec and Basic Upgrade
The Clutch Industries Premium Clutch Kit is a comprehensive package designed and manufactured specially to be a direct replacement for the OE clutch. The Clutch Industries Premium clutch kit is designed for stock vehicles which don't require any fancy bells and whistles, just a direct replacement for the original clutch. Reliable is a term which best describes this clutch kit with a Quality Assured series of replacement parts which will meet or exceed the requirements and performance of the original equipment. The Clutch Industries Premium clutch kit features an ultra-durable chrome vanadium diaphragm, forged clutch disc hubs, flywheels balanced to less than 70 gcm (gram centimetres), release bearings tested to 1,500,000 cycles at 180 degrees Celsius and premium friction materials for great torque capacity.
If you require a little more performance from your clutch kit without going too crazy or sacrificing on driveability, the Clutch Industries Heavy Duty kit is the pick of the bunch. This clutch kit is a tough, no-nonsense clutch upgrade. These kits have been engineered to handle heaps of torque and endure the stringent demands of workhorse vehicles. For those who demand relentless reliability, the Clutch Industries Heavy Duty Clutch Kit is ideal for vehicles regularly subjected to demanding driving conditions including towing, light engine modifications and trade use. These clutch kits feature a minimum of 20% increase in torque capacity for reduced slip and increase in power delivery over a wider horsepower range. These clutch kits offers a powerful, next level upgrade to standard clutch kits.
Are you an avid 4x4 enthusiast? Clutch Industries have a clutch just for you. The 4 Terrain Heavy Duty clutch kit range is designed to handle high torque loads leaving standard clutch kits in the dust when it comes to performance. These clutch upgrade kits are designed for towing boats, caravans or camper trailers, high weight loads when carting heaps of off-road gear including fridges, bull bars, winches or roof top tents and trade or commercial use. With patented ER2 technology in the clutch cover, 4 Terrain HD (heavy duty) kits offer an increase in torque holding when compared to standard clutch kits for an approximate 20% increase in clamping force than a standard clutch kit. These clutch kits also gain torque holding capacity from Spheroidal Graphite Iron (SG Iron) grooved pressure plates. These grooves assist in heat dissipation and increase the Mean Effective Radius, offering an all-round better performing clutch with higher torque and heat resistance.
If the 4 Terrain Heavy Duty Kit just won't cut it for your 4x4, we recommend the 4 Terrain Ultimate ER2 for more serious off-road rigs. With an impressive list of features that make this clutch kit unique, it really is a step above the rest when it comes to a high-performance clutch tailored specifically to the needs of aggressive off-road driving. With a combination of advanced friction materials, clutch covers and clamping forces, 4 Terrain Ultimate Clutch Kits boast an impressive 60% higher torque rating than a standard kit which makes them great for serious off-road thrashing through muddy bog holes, sandy beaches or fast river crossings. The clutch cover incorporates premium corrosion resistant characteristics to ward off weathering over a long period of time, even when dunking your car's undercarriage in water-crossings. The clutch cover in 4 Terrain Ultimate kits is manufactured from Spheroidal Graphite casting material which offers 300% more strength than standard castings. The clutch pressure plate incorporates 4 Terrain Ultimate-exclusive ER2 design technology with ER2 grooves machined using CAD/CAM technology to enhance performance in multiplate ways. This technology increases torque capacity of the clutch and also aids in heat dissipation, increasing torque capacity allowing the clutch to grip harder for longer. 4 Terrain Ultimate clutch kits also feature an aramid friction material on the clutch disc. This friction material offers 50% less wear than conventional materials and also aids in reducing clutch fade as temperatures rise.
Passenger Performance Upgrades
Mantic Clutch is the serious performance division of the Clutch Industries range. With specialised clutch systems suitable for lightly modified street cars all the way up to four-digit horsepower track weapons, there is a Mantic Clutch kit to best suit the balance of performance and driveability for you. The Mantic 'Stage' series are a range of single-disc clutch systems designed for street and track applications and are available in varying levels of seriousness depending on how much power you're pushing and how you treat the car.
The Mantic Stage 1 and Stage 2 clutch kits are the best Mantic Clutch kits for street driving applications. These exhibit little to no compromise in drivability, whilst still boasting impressive gains over a standard clutch kit. These clutch kits are suitable for cars with a little extra power from a mild tune with a few small upgrades such as air intakes, aftermarket exhaust systems or other basic mods.
Stage 1 and 2 kits utilise patented CNC machined ER2 Groove Design on the friction surface of the pressure plate to increase Mean Effective Radius and also aid in heat dissipation to allow the clutch to grip harder for longer with a significant increase in torque capacity. The Stage 1 clutch kit uses an organic clutch disc which when paired with the ER2 grooved pressure plate offer up to a 40% increase in torque capacity over the OE clutch with no compromise on street driveability. The Stage 2 clutch kit uses an upgraded cover and an organic / cerametallic clutch disc paired with the same ER2 grooved pressure plate to offer up to an 80% increase in torque capacity with very minor compromises when it comes to street driveability.
The Mantic Stage 3 Clutch Kit is designed for powerful street cars with significant road-legal modifications, however this clutch is still suitable for occasional track use and has been designed to stand up to the abuse of driving on racetracks every once in a while when you really want to open up the throttle. These clutch kits are ideal for those who like to carve up mountain passes, take regular spirited drives in their modified street cars but aren't afraid to hit the track occasionally for some fun, safe and legal door-on-door racing, quarter mile sprints or skid pan antics. The Mantic Stage 3 Clutch Kit uses an upgraded cover assembly, sprung cushioned ceramically disc and spheroidal graphite iron pressure plate to offer 100% torque capacity increases, that's double the torque holding of a stock clutch!
At Stage 4, Mantic Clutch Kit range really start to take off. Stage 4 kits are recommended predominantly for motorsport use with modified track cars requiring impressive torque capacity where driveability comes second to speed. These kits aren't for the faint of heart and utilise an un-dampened cerametallic disc for aggressive clutch engagement making power delivery swift, sharp and precise when down-shifting into a corner, banging gears down the pit straight or clutch kicking your drift car. Mantic Stage 4 Clutch Kits offer up to a 100% increase in torque capacity which is double that of the stock clutch!
The Mantic Stage 5 Clutch kit is the most aggressive single disc clutch in the Mantic range. This clutch kit is suited to seriously modified, high horsepower, high RPM track vehicles which are used only on the track and regularly in demanding motorsport applications which require serious torque capacity, precise clutch engagement and instant power delivery. The rigid centre and undampened cerametallic disc make clutch engagement aggressive yet reliable with minimal slip, instant engagement and 100% increased torque capacity over the stock clutch, that's double the power of a factory-fitted clutch kit! Burst-proof castings also cater to extremely high-revving engines with materials designed to cope with the forces of spinning at high RPM, keeping the driveline both safe and reliable.
The Mantic Street Twin Clutch Kit with sprung centre and cushioned cerametallic discs is available in twin or triple-plate configurations, this clutch kit offers a level of performance that surpasses its organic equivalent. This clutch kit is still suitable for street driving, however with literally thousands of Nm of torque capacity, these clutches are ideal for driving to the shops to pick up groceries on Friday and unloading upwards of 2000Nm of torque in your turbo grocery-getter at the track on Saturday. The twin plate configurations of this clutch kit is suitable for up to 2,050Nm of peak torque, while the triple-plate variant can deal with a whopping 3,075Nm of peak torque.
The Mantic Sport Rigid Centre Cushioned Cerametallic clutch kit is designed for harder driving styles, still with some consideration to driveability and an amount of dampening. These clutches are designed for high-horsepower, high torque motorsport applications where the driver prefers a slightly less aggressive feel and an element of smoothness. These clutch kits are ideal for track-focussed race cars, time attack cars, sprint cars, drag racing cars and drift cars. The twin-plate configuration of this clutch is rated to hold up to 2,050Nm of torque, while the triple-plate option is rated to hold up to 3,075Nm of torque. The Mantic Sport Rigid Centre Undampened Cerametallic Clutch Kit is not for the faint hearted. This is the most serious, aggressive and high-performing clutch kit that Clutch Industries and Mantic have on offer. If you need instant engagement, little chance of slippage, high torque capacity and all round performance that puts comfort second to speed, this is the clutch kit for you. The twin plate configuration of this clutch is rated to hold up to 2,050Nm of torque while the triple-plate option is rated to a whopping 3,075Nm of torque.
- Spheroidal Graphite – Also know as SG iron or ductile iron, this material is a type of graphite-rich cast iron which exhibits high levels of resistance so impact and fatigue.
- Mean Effective Radius – Mean effective radius refers to the distance from the centre of the friction plate to the centre of the friction material. Friction plates with the same outside radius but with a larger inside radius will have a higher torque capacity when compared to one with a smaller inside radius.
- Moment Of Inertia – The rotational mass of a rigid body. A lower moment of inertia or rotational mass means that the engine and rotating assembly can spin faster, similar to why.