What you need to know before replacing the clutch

Replace clutch

Almost every car is equipped with a clutch. Using a friction disc, pressure plate and flywheel, the clutch ensures that forces generated by the engine are converted to movement in the gearbox. The clutch is a wearing part making it necessary to replace it once in a while.

There is no set interval for clutch replacement. This is because it depends on driving style, type of mileage (city driving, highway) and the car’s power. With a lot of highway traffic and a quiet driving style, clutch replacement may not be necessary until 250,000km or later, while a sporty driver with a lot of city mileage may have worn out the clutch as early as 140,000km.

Typically, a clutch will last between 170,000 and 250,000km before it is worn out and needs to be replaced.

To give a clear picture of why a clutch needs to be replaced, below is a brief explanation of how the clutch works.

What is the function of a clutch?

The clutch ensures that the forces produced by the engine are transferred to the gearbox and thus the entire driveline. When shifting gears or standing still, the connection between the motor and clutch must be disconnected so that no drive is present.

How does a pairing work?

The clutch system in a car consists of a number of important components:

• Master clutch cylinder
• Auxiliary clutch cylinder
• Flywheel
• Friction disc
• Pressure group
• Thrust bearing

Flywheel

The flywheel is a solid round disc mounted directly on the crankshaft of the engine. A flywheel is good for 2 things:

1. Making the engine more comfortable:
   Usually a flywheel is fairly heavy (8-15kg), this provides ride comfort and allows the motor to work properly. Why? If an engine has a heavy flywheel, then when the engine is coasting the engine will not “drop dead” right away, but quietly drop in rpm because this large mass does not just come to a stop. Moment of inertia plays the most important role in this, the heavier an object is the harder it is to get going but also harder to slow down.

   When installing a lightened flywheel, the engine will respond much brighter; this can be fine for sporty or track use. In daily traffic, this results in a more nervous engine and will also stall more easily than an engine with a heavy flywheel. Again, this has to do with the moment of inertia. Lighter mass stands still easier and faster than heavy mass.

2. Serve as a friction surface for the clutch plate:
   In a clutch system, forces must always be transferred from the engine to the drive. The flywheel provides the friction part on the engine along with the pressure group.

Friction disc/coupling plate

The friction disc or clutch plate is in direct connection with the gearbox. There are teeth inside the clutch plate which slide over the gearbox input shaft.

Once the clutch pedal is depressed then the auxiliary clutch cylinder disconnects the connection between the flywheel, clutch plate and pressure plate. The flywheel and pressure plate will spin when the engine is on and the clutch plate will be stationary when the car is not rolling.

When the clutch is released, the pressure plate will again apply pressure to the clutch plate and clamp it between the pressure plate and the flywheel. During this process, a brief slip occurs (when starting off) and then a “solid” connection which converts the drive from the engine to the gearbox. This slip in the clutch wears out the friction material and a clutch should be replaced after x number of kilometers.

 

Pressure group

On top of the clutch plate comes the pressure plate. This is bolted to the flywheel and thus is in direct connection with the engine and also always turns the same speed as the engine along with the flywheel. The only part that does not always rotate with the engine is the clutch plate because it is in direct connection with the gearbox.

As its name implies, the pressure group ensures that, under normal conditions, a large amount of pressure is applied to the clutch plate. This “sandwiched” as it were the clutch plate between the flywheel and pressure group to make this one solid connection and transfer forces to the gearbox.

When pressing the clutch (auxiliary clutch cylinder), the thrust bearing will press against the fingers (black triangles in the picture) of pressure group which will then break the connection.

 

Main clutch cylinder/Auxiliary clutch cylinder

The master clutch cylinder is bolted to the bulkhead and is in direct connection with the clutch pedal. Once the clutch pedal is depressed, pressure builds up on the line to the auxiliary clutch cylinder and the brake fluid/clutch fluid wants to move.

The auxiliary clutch cylinder is attached to the gearbox or inside the gearbox. This ensures that the forces of the clutch pedal are converted into movement of the thrust bearing. The thrust bearing (pictured with the blue plastic) will now exert force on the pressure plate which causes the connection between the gearbox and engine to be broken.

 

Do you choose a standard clutch or a racing clutch (4-6 puck)?

Before replacing a clutch, a choice will have to be made as to which clutch will be replaced. In the case of a standard car, the choice is usually quickly made and an original/standard clutch will be installed.

For cars that have products from LucaCarMods.com this will be different, these often have more power than original or drive a lot more sporty. We offer a Competition Clutch Stage 3 and a Stage 4 for these riders. These clutches are more than suitable for drifting or for cars with a turbo fitted afterwards.

The material of these couplings is of a different, more expensive composition which ensures that it can withstand heat better and is less likely to slip.

Competition Clutch Stage 3

The manufacturer states that this clutch is suitable for a power increase of 150%. On the turbocharged Mazda MX-5s we build, this is the most commonly used clutch. The pedal feels almost like original, the clutch does not engage aggressively, and it has proven itself on Mazda MX-5s rated 280-300HP. Originally, a Mazda MX-5 has between 90 and 140hp….

Competition Clutch Stage 4

If you go drifting very often, have above 300hp (In the case of a Mazda MX-5) or want a clutch that engages more aggressively then the Competition Clutch Stage 4 is the best choice. It is suitable for power increases of 150-200% and will engage more aggressively than the original clutch. My personal experience is that the Stage 4 is still fine to drive as a daily car in terms of gripping but traffic jam driving is less pleasant.

Lifespan of a racing clutch

About the life of a Stage 3 or 4 clutch depends greatly on what it will be used for. With normal use, it will be able to last as long or longer than an original clutch. With modified use such as; drifting, drag racing or track driving, there is pretty little to say about service life because it depends on too many factors.

Purchase advice from LucaCarMods.com

Purchasing a clutch is very personal, to get you started we have advice based on 3 different situations.

1. Original car – no ambition to drift or more power in the future.
   A replacement clutch is sufficient and will typically last 170,000km before needing to be replaced again.
2. Adjusted power +50/75% – sporadic drifting and/or track use
   You are asking significantly more of the clutch due to the extra power. Track driving and especially drifting will also generate a lot more heat. An original clutch will wear out very quickly or slip immediately. A Stage 3 clutch is the perfect solution in this situation.
3. Adjusted power +100/175% – regular drifting and/or track use
   The stage 3 clutch may struggle in certain situations with this use and power. With this level of power i.c.w. drifting, a Stage 4 clutch is a must! This one can take even more heat and will engage many times better.