Problems and solutions of air in the hydraulic clutch system

 I. Analysing the problem of air in the hydraulic clutch system

When air is mixed in the hydraulic clutch system, the following problems will occur:

1. Abnormal pedal feel

   - Phenomenon: The clutch pedal becomes ‘soft’, and the stroke feels longer and the force feedback is weaker. Cause: The compressibility of air is far more than that of air.

   - Cause: The compressibility of air is much greater than that of hydraulic fluid, resulting in an increase in pedal travel and poor actual separation.

2. Incomplete separation

   - Phenomenon: The clutch cannot be completely disengaged, resulting in difficulty in shifting gears, and the feeling of ‘not being able to hang the gear’ or ‘hitting the teeth’ when shifting gears. Cause: The presence of air makes the clutch not completely disengage, resulting in a longer stroke and weaker feedback when pedalling.

   - Reason: The presence of air prevents the clutch from generating enough hydraulic pressure to push the clutch disc when it is pressed, thus preventing complete disengagement.

3. Increased freewheeling stroke

   - Phenomenon: The freewheeling stroke of the clutch may increase after air is introduced into the clutch parting pump.

   - Cause: Free travel is the travel required for the clutch pedal to start disengaging the clutch disc from the initial position. An increase in free travel means that the driver needs to depress the pedal more deeply to disengage the clutch, which can affect driving comfort and operating precision.

4. Strange noises and difficult gear changes

   - Phenomenon: Air in the hydraulic clutch system can also cause rattling and difficult gear changes.

   - Cause: Rattles can be caused by vibrations and shocks caused by air travelling through the system, while gearshift difficulties can be caused by the clutch failing to fully disengage or engage.

5. Damage to Transmission Gears

   - Phenomenon: If the air problem in the hydraulic clutch system persists over a long period of time, it may cause damage to the gears of the transmission.

   - Cause: The clutch does not fully disengage or engage, resulting in excessive shock and wear on the gears of the transmission when shifting gears, thus shortening the service life of the transmission.

6. Reduced operational responsiveness

   - Phenomenon: The compression and sudden release of air bubbles under high pressure creates additional vibration and noise, affecting driving smoothness and control accuracy.

   - Cause: The presence of air increases the internal resistance of the system and reduces the amount of hydraulic pressure that can be effectively transmitted, thus reducing the efficiency of the entire clutch system.

7. Reduced system efficiency

   - Phenomenon: The presence of air increases the internal resistance of the system and reduces the hydraulic pressure effectively transmitted, thus reducing the efficiency of the entire clutch system.

   - Cause: Air in the system causes unstable hydraulic pressure and affects the normal operation of the clutch.

8. Cavitation

   - Phenomenon: The long-term presence of air may lead to cavitation in the hydraulic system, causing damage to the hydraulic components and further affecting their service life.

   - Reason: Cavitation is caused by the rupture of air bubbles under high pressure, causing erosion on the surface of hydraulic components.

 Second, the hydraulic clutch system into the air solution

1. Exhaust air

   - Step: The air in the hydraulic system needs to be vented. This is usually carried out through the hydraulic system exhaust screw, need to exhaust while slowly depressing and releasing the clutch pedal until all the air has been discharged and the hydraulic fluid completely filled the system.

   - CAUTION: Ensure that there is no excessive loss of hydraulic fluid during the venting process and replenish the hydraulic fluid if necessary.

2. Checking and Changing the Hydraulic Fluid

   - Procedure: Prior to air venting, old or contaminated hydraulic fluid should be checked and replaced to ensure that there is fresh hydraulic fluid in the system.

   - NOTE: Use hydraulic oil that meets the manufacturer's recommendations and avoid using unsuitable oil.

3. Checking for Leaks

   - Procedure: Check for leaks in the hydraulic system, as leaks may cause air to enter the system.

   - Caution: Focus on checking line fittings, cylinders, seals, etc. to ensure that all connections are well sealed.

4. Professional Maintenance

   - Procedure: If you are unable to solve the problem by yourself, it is recommended that you seek the help of a professional mechanic to ensure that the air is properly vented and the system is checked.

   - Note: A professional mechanic has a wealth of experience and specialised equipment and is able to diagnose and solve problems more accurately.

Ways of air entering the hydraulic clutch system

1. Entry during servicing

   - Disassembly and reassembly: When the hydraulic clutch operating system undergoes overhaul or maintenance, such as disassembling and reassembling the piping, cylinder and other components, air may take advantage of the opportunity to enter the system if it is not handled properly or sealed properly.

   - Incomplete air venting: If the air venting operation is incomplete after overhauling, the air trapped in the system may cause problems in subsequent use.

2. Changes in brake fluid

   - Decrease in brake fluid: When the fluid level of the clutch reservoir is lowered considerably, air may enter the hydraulic system through the gap between the fluid level and the reservoir cap.

   - Adding brake fluid: Improper handling when adding brake fluid, such as using improper tools or methods, may also cause air to enter the system.

3. Seal failure

   - Deterioration of seals: Over time, seals in the system may deteriorate or wear out, resulting in a loss of sealing performance, which allows air to enter the system.

   - Improper installation of seals: When replacing or installing new seals, if they are not installed properly or the correct sealing material is not used, this can also lead to air leakage into the system.

4. Changes within the system

   - Temperature Changes: As the temperature of the system changes, so does the solubility of air in the fluid. As the temperature increases, air dissolved in the fluid may precipitate out and form bubbles.

   - Deterioration of the fluid: If the fluid is used for a long period of time or is contaminated, its properties may change, such as reduced viscosity, oxidation, etc., which may result in air bubbles being more likely to form in the fluid.

SUMMARY

Air mixed in the hydraulic clutch system will lead to abnormal pedal feel, incomplete clutch disengagement, increased free travel, abnormal noise and difficulty in shifting, as well as possible damage to the gears of the transmission and other problems. Therefore, it is vital to remove air from the system in a timely manner and take appropriate preventive measures. Regular inspection and maintenance of the hydraulic clutch system to ensure that no air enters is a key measure to keep the clutch working properly.