The first time you go to a driving school, you are taught that the clutch pedal allows you to smoothly start the car movement and change gears if you’re learning to drive on a manual transmission car. But for many drivers what’s going on behind the pedal remains a mystery.
Have you ever wondered what happens inside the car when you press the clutch pedal? Or why do you have to press the clutch pedal before changing gears in a manual transmission? In this article, accompanied by an explanatory video, we will give you answers to these questions.
To understand the need for a clutch, let’s first understand the anatomy of an internal combustion engine car!
Internal combustion engines have a very limited torque band. For this reason, to effectively change the wheel speed, internal combustion engine cars need a transmission system.
Using the transmission makes the engine run at optimum rotational speed/minute. And by changing the gear depending on the driving conditions, the transmission helps control the speed of the wheels.
In a car with a manual transmission, changing gears is not an easy task. To have an easy speed change with a manual transmission, the power flow of the engine to the transmission must be interrupted.
However, it is not practical to stop the engine just for this gear shift. The clutch is used for this purpose. In short, the clutch is a mechanism for disconnecting the power flow from the transmission without stopping the engine.
Let’s understand how the clutch works!
We will list the clutch of a manual car because the automatic car is more complicated regarding its transmission and we will cover it in another article.
- Clutch disc
- Pressure plate
- Pressure bearing
The main part of the clutch consists of a disc covered with high friction material on both sides. This disc is on the flywheel. If an external force presses on the clutch disc, it will also rotate with the flywheel, due to the frictional force.
The input shaft of the transmission is connected to the disk. Thus, when an external force is applied to the disk, the power of the engine will be transmitted to the transmission system.
This external force is provided by a pressure plate with a spring system. The lid of this system is firmly attached to the flywheel. Thus, the pressure plate will firmly press the friction clutch disc, and the engine power will be sent to the transmission system. But this is the case with normal management. So, how is the power disconnection done with the clutch?
For decoupling, a special type of spring is introduced into the pressure plate assembly. This spring is known as the diaphragm. To better understand this diaphragm spring, you better assume that the movement of the diaphragm spring is fixed around this circle.
In this case, if you press the center part of the spring, the outer part must move in the opposite direction. The diaphragm spring is located between the pressure plate and the lid. The outside of the diaphragm spring is connected to the pressure disc.
This means that if you press the inside, the pressure disc will move from the rubbing disc. Thus, the power flow will be switched off from the transmission. This is exactly what happens when you press the clutch pedal.
A hydraulic system transfers the movement of the clutch to the center of the diaphragm spring. When this spring is pressed, the power flow is interrupted.
During this time you can perform a gear shift. The clutch pedal is released after changing gears and the power flow continues again. This is how the clutch works.
In a real clutch, you can see a few coil springs on the clutch disc. What is the purpose of these springs? They are used to smooth out fluctuations and vibrations from the engine output.
The hub and disc are not connected directly. The power of the engine first reaches the disk, then transfers to the springs, and finally to the output hub.
This means that the springs will alleviate most of the power fluctuations and the movement transferred to the vehicle will be much smoother.
The problems of a clutch and the symptoms of failure
It is a fact that the clutch of a car will wear before the car, even under normal conditions, it will be used quite a lot because of the permanent change of speeds. So how long does the clutch lasts in a car with a manual transmission?
The reality is that it is impossible to answer because they are so variable. You’ve probably heard from people who say their clutch has worn below 30,000 miles.
Others will tell you that they work perfectly and at 100,000 miles. This difference in clutch lifespan depends on how the clutch is used and where it is used
The most common problem with clutches on a manual transmission is that they start to slip. You will be able to see this manifestation if the RPM counter goes crazy when you accelerate.
The feeling is like holding the clutch pedal and accelerating at the same time, even if you don’t press the clutch.
So if you see this symptom, the car accelerates more slowly and you can no longer climb the slopes with the same ease as before, then surely the problem is a slipping clutch.
Why is the clutch slipping?
The frictional force between the clutch disk and the flywheel is responsible for the correct functioning of the clutch kit. If this friction coefficient is lower than usual, the coupling from the engine to the transmission is no longer correctly and fully transmitted, and the contact surfaces begin to slip.
Because of this, the clutch performance is way down, and it’s better seen when trying to accelerate the car. It will take much longer.
What are the common symptoms of a slipping clutch?
The smell of burning in the car cabin. If you feel a burning smell in the car more often, this is a strong sign that the clutch is worn.
Problems with changing gears from one stage to another. You will notice that when you want to change gears, the lever will work harder, you will have to pull harder to change gears.
The engine revs but accelerates more slowly. As we explain above the obvious symptom that the clutch slips is that the RPM counter is always up when you accelerate, because of this the car accelerates very hard and is quite annoying.
The engine revs, but the car does not move at all. This symptom indicates that the clutch has completely given up. Basically, the clutch pressure plate pads have worn out to the maximum and do not engage at all. In this case, no matter how much you press the accelerator, the speed will increase, the car will stay still, and the RPM counter will be at high values.
If the gears are difficult to change, especially at low temperatures, it most often means that there is a problem with the pressure plate. If this component does not work properly, the clutch flywheel will not be fully disconnected and the car must be checked by an accredited car mechanic.
If you notice under the clutch pedal, on the mats, moisture, or leaking liquid, or in the engine compartment, fluid leaks in the area of the hydraulic pump, it is very important to go immediately to a car workshop. These leaks are symptoms of a bad clutch, of a failing component, the hydraulic cylinder
A slipping clutch is a common fault caused by driving mistakes and a lack of interest to handle the clutch correctly.
Driving with a slipping clutch is uncomfortable and dangerous. In most cases, every driver can prevent these problems by eliminating bad habits that lead to a failing clutch faster.
Bad habits that lead to fast clutch wear
- If the clutch is often used on a bad road, and if it is used every day in a crowded area with frequent and sudden presses of the clutch, this aspect will damage the clutch a lot.
- The driving style of a car is very important for the lifespan of the clutch. If the driving style is bad, then expect to change the clutch more often.
- Try not to use the clutch pedal to support the foot when the car is running. This habit is very bad and harmful to the clutch.
- The fact that you do not press the clutch pedal to the bottom is another harmful thing for your clutch. Also, holding down the clutch pedal at an intersection is not a good thing. If you want to prolong the life of your clutch, try to eliminate these habits.
Other clutch faults
- When the pressure bearing fails, it will produce a specific noise and vibration when the clutch pedal is pressed. Also, if changing gears is difficult, we say that it would be best to order a new clutch kit because the current one will not last long.
- At the same time, as I said in other articles, it is best to call an authorized service, because at this operation the gearbox must be disengaged, so many parts will be removed and it would be good to be reinstalled by responsible persons with the experience.
- If you have a more sporty driving style then the kit will not last you much. But if you have a more calm and correct driving style, then it can keep you without problems and over 100,000 miles.
- If you see that you have to press harder on the clutch pedal or, on the contrary, it is softer and its position is not normal, then it is good to go to service because the pedal can lock. In this situation, the lever connected to the pressure plate is worn and needs a replacement, or the hydraulic pump no longer works.
As for the best clutch kits, we always recommend buying a LuK clutch kit or Sachs clutch kit
Let’s talk a little about clutch kits for modified cars
Modified clutch kits
There are also clutch kits modified (or made/reinforced) with Kevlar or ceramic tiles. Let’s start with the Kevlar-reinforced clutch. Well even after a “stage 1” for the car, the clutch disc will be much more in demand (especially in diesel engines where the torque increases significantly and destroys everything in the way).
So the first solution would be to change or strengthen the old disc. It will replace the friction material with Kevlar which is much more resistant, especially at high temperatures.
This would be the first clutch option after a small power increase. Also, even if the clutch disc has been reinforced, you have to think seriously, either you get it hardened and the pressure plate or simply do not ask too hard, because it will overheat and at the same time the pressure plate will “tire” faster if subjected to greater forces.
A reinforced clutch with Kevlar allows you to drive”daily” because the coupling will be a little more aggressive but it can still be driven regularly through the city. This operation also resorts to cargo vans that go all day with a full car or drivers who tow trailers/platforms/ caravans.
A second option, if you greatly increase the power of the car, would be opting for a clutch kit reinforced with ceramic plates. If you opt for such a clutch, you will no longer be able to drive the car daily, or you can but very difficult because the clutch coupling is almost instantaneous, there is no progressive coupling.
This type of clutch comes with advantages but also disadvantages. For example, such a clutch kit, which includes the hardened plate and pressure bearing, a clutch disc reinforced with ceramic plates will withstand very high powers.
But a major disadvantage would be that there is no possibility of progressive clutch coupling (you will always go with “screeching”) and thanks to the fact that the coupling will be very aggressive and abrupt, usually, the gearboxes do not last too long.
Some gearboxes also dropped after 2,000 km. The clutch is very durable but not the gearboxes, so you have to consider all these aspects.
Whatever you do, it would be best to turn to a professional service, with seniority and good reviews, because this operation is very complex and if not done properly you can have big problems further.