Over the years, manual transmission vehicles have had two main types of clutch movement: mechanical and hydraulic. Many older cars use a mechanical or cable system, whereas almost all modern cars use a hydraulic clutch.
Manual transmissions, or stick-shift/standard transmissions, are equipped with a clutch pedal that the driver presses to disengage the clutch. The clutch pedal, then, must be connected to the clutch by some system of components. This can be a clutch cable, or a hydraulic clutch system.
What is a Hydraulic Clutch?
Hydraulic clutch systems are typically easier to press than a clutch cable system, but they are more complicated. In the hydraulic clutch system, the clutch pedal is attached to the clutch master cylinder, which pushes hydraulic fluid through the system with great force.
To transmit the pedal movement, a hydraulic clutch mechanism uses a hydraulic line instead of a mechanical connection (eg: a Bowden cable). A piston on the master cylinder at the pedal transmits the pressure through a fluid to the piston of the slave cylinder at the clutch operation on the transmission.
That fluid cannot be compressed, so when the clutch master cylinder presses the fluid through the system, it travels through a hose and moves the clutch slave cylinder.
This chain reaction continues as the clutch release fork, which is moved by the clutch slave cylinder, pushes the clutch release bearing (a.k.a. throwout bearing) into the clutch pressure plate, releasing the clutch.
This is a seemingly complicated system, but it is actually very much like any other hydraulic system, including the brakes.
How Does a Hydraulic Clutch Work?
The hydraulic clutch works like the brake hydraulics system in your car. The clutch pedal is connected to a master cylinder. When you push the pedal, a rod in the master cylinder pushes fluid out into lines and hoses that go to a slave cylinder. In turn, this slave cylinder pushes on a fork, which moves the clutch away from the flywheel.
Unlike a mechanical clutch, a hydraulic clutch doesn’t have a cable that can stretch and brake. Pedal feel remains consistent, and the system automatically adjusts itself. That means you get the same pedal feel and engagement point throughout the clutch’s life. However, fluid leaks and air in the system can keep the clutch from disengaging.
Working Principle of a Hydraulic Clutch:
The working procedure of the Hydraulic Clutch is usually divided into two parts. One is Engagement and another one is Disengagement. The following section discusses the same concisely;
Engagement:
- At first, the Clutch pedal has to be pressed by the driver of a vehicle to start the engagement process.
- When the clutch pedal is pressed then it starts the working process of the diaphragm Clutch.
- The clutch pedal is attached to the clutch plate. Therefore, the clutch plate starts its rotation.
- The friction surfaces of the clutch plate can be used to make contact with the pressure plate and also flywheel.
- The pressure plate gives pressure to the spring and spring makes contact with the splined sleeves.
- Then the attachment of pressure plate, splined sleeves, friction surfaces, clutch plate, and the flywheel is made and the engagement is done in this way.
Disengagement:
- At first, the Clutch pedal has to be released by the driver of a vehicle to start the disengagement process.
- The splined sleeves come backward and release the contact of the pressure plate and the clutch plate.
- Then the flywheel also released from the contact of the clutch plate.
- The rotation of the clutch plate becomes slows down and at last stops.
- Then the disengagement process is done in this way.
Parts of a Hydraulic clutch
The Hydraulic clutch is made of different types of components. They are as follows:
- Clutch Pedal
- Diaphragm Clutch
- Clutch Plate
- Friction Surface
- Pressure Plate
- Flywheel
- Diaphragm Spring
- Splined Sleeves
1. Clutch Pedal
Most primary part that engages the clutch in vehicles is the Clutch Pedal. A driver has to press the clutch pedal to start the engagement process. At first, after pressing the clutch pedal, the clutch plate starts its rotation.
2. Diaphragm Clutch
Diaphragm Clutch is usually an independent clutch, but in Hydraulic Clutch the Diaphragm Clutch can be used. The diaphragm Clutch is attached to the clutch pedal.
When the clutch pedal is pressed by the driver then at first, the clutch pedal pushes the Diaphragm Clutch then the other diaphragm Clutch presses the flywheel to do further processes.
3. Clutch Plate
One of the most important parts of the Hydraulic clutch is the Clutch Plate. The clutch plate is made of thin metal plates. There is a friction lining present, which is attached to the clutch plate, on both sides.
Apart from that, this clutch plate is usually placed among the pressure plate and the flywheel. The friction lining of the thinner surface of the clutch plate makes its contact to the flywheel and the friction lining of the outer surface of the clutch plate and that makes contact to the pressure plate and makes the friction.
4. Friction Surface
Friction surfaces are attached to the clutch plate on both sides. When the clutch plate starts its rotation then the friction surface makes contact to the pressure plate and also to the flywheel. Therefore, the friction force is generated. This friction force makes the high torque.
5. Pressure Plate
Another useful part of the Hydraulic clutch is the Pressure plate. The pressure plate is placed on one side of the clutch plate. The pressure plate is attached with springs with the help of the bolts and along with the clutch pedals.
The friction surfaces of the clutch plate make contact with the pressure plate. The pressure plate’s function mainly depends on weight. When weight is given to the pressure plate then it makes contact with the friction surface of the clutch plate and produces the friction.
6. Flywheel
Another useful part of the Hydraulic clutch is Flywheel. The flywheel has placed on another side of the clutch plate. The flywheel is attached to the transmission shift. The friction surfaces of the clutch plate make contact with the flywheel. So, friction is produced.
7. Diaphragm Spring
Diaphragm Spring is attached to the pressure plate. These springs mainly work, with the help of the pressure plate. This pressure is produced from the high weight, that is given to the pressure plate. Along with that, thrust spring makes contact with the friction surface of the clutch plate and produce high friction.
8. Splined Sleeves
Splined sleeves are mainly used to make engagement and disengagement in the multi-plate clutch system or mainly in the Hydraulic clutch system. These Splined sleeves are placed between the friction lining of the clutch plate and the pressure plate.
When pressure plate gives pressure then the splined sleeves used to go forward to make the clutch engaged and when the pressure plate releases the pressure then the splined sleeves used to go back to make the clutch disengaged.
Symptoms of Bad Hydraulic Clutch System
The clutch is a vital part of a manual transmission and in the hands of an experienced driver, will last well past 120K miles.
If it’s damaged or severely worn, you’ll experience difficulties which could ultimately lead to transmission issues or issues where you are not able to accelerate – ultimately known as “clutch slippage”. Fortunately, there are multiple signs to inform you when something is wrong with your clutch.
- A clutch will not disengage when pressed.
- Grinding noise on every shift or inability to shift gears with the engine running.
- The clutch pedal is light or moves too easily.
- Fluid dripping from the hydraulic clutch system.
- The vehicle attempts to move forward with the clutch pressed.
- The clutch fluid reservoir is low or empty.
Related Repair Advice for the Hydraulic Clutch System
- If the clutch pedal cannot be pressed, the hydraulic system is likely in good working order, but mechanical clutch components may be damaged.
- Many vehicles will use brake fluid for the clutch, but check the owner’s manual and the clutch fluid reservoir cap for the proper fluid type when refilling.
- When air is found in the hydraulic clutch system, bleeding the air from the clutch slave cylinder is only a temporary fix, and finding the entry point for the air is required.
- Most hydraulic clutch components can be replaced without removing the transmission, unfortunately, replacement of the clutch or clutch release bearing requires transmission removal to access those components.
- Continuing to drive a vehicle with a defective hydraulic clutch system may result in internal transmission damage, especially synchronizer damage.
Advantages of a Hydraulic Clutch:
There are many advantages of the hydraulic clutches. Some of the advantages are stated below:
- The hydraulic clutch is self-lubricated so the hydraulic clutch needs no maintenance for the lubricating clutch.
- In the case of a hydraulic clutch, the height of the pedal is adjusted automatically.
- In comparison to the other clutch systems, the hydraulic clutch can give an easier feeling during pushing the clutch.
- There are many variations present of the hydraulic clutch so this clutch can be fitted at any place.
- Due to corrosion the, inner wires used in the mechanical clutch may bend so mockingly the wires can get stuck. This incident can lead the damage to the clutch. But in the case of the hydraulic clutch, this type of damage is not possible. Because a replacement of a particular fluid in the hydraulic clutch is enough to prevent the above type of damage.
- Losing the cable after some time affects the disengagement process that may damage the clutch completely. But in the case of the hydraulic clutch, there is no cable required so this clutch is safe from damage caused by loosening the cable.
- So, using a hydraulic clutch instead of another clutch is safer and more reliable.
- It is better to use the hydraulic clutch because of its quality. The quality of this hydraulic clutch is better than the mechanical clutch
Disadvantages of a Hydraulic Clutch:
There are many disadvantages of the hydraulic clutches also present. Some of the disadvantages of hydraulic clutches are stated below:
- The hydraulic clutch consists of some mechanisms such as the slave cylinder and cylinder are the two mechanisms of this clutch. So, there is a chance of outflow of fluid that can be used in the hydraulic clutch. This outflowing happens from the cylinder as well as from the slave cylinder due to the damage that results in the leakages. For repairing this damage, users have to spend extra money.
- This hydraulic clutch consists of plastic metallic piping systems. This pipe is breakable or can be torn down. So, from time to time checking is necessary. This is more expensive to maintain damage prevention.
- For proper functioning, standard and correct fluid is required otherwise seals may be damaged. So, maintaining the standard for proper fluid can be a little more expensive.
- From time to time checking the level of fluid of the hydraulic clutch is compulsory for users.
- The price of the hydraulic clutch is more expensive than the mechanical clutch. This is one of the most crucial disadvantages of this clutch.
Application or Use of the Hydraulic Clutch:
Most of the reputed car manufacturers are opting for the hydraulic clutch for their products for quality and simplicity in applications. Nowadays the use of hydraulic clutches is highly observed in trucks and automotive industries also. Due to the features of self-oiling or lubrication, auto -adjustment, low effort to the actual adjustment, the hydraulic clutches are used in various systems.