Throwout Bearing Overview

 Clutch Release Bearing Definition

A clutch release bearing, also known as a throwout bearing or release bearing, is a key component in the clutch system of a manual transmission. Its main function is to help engage and disengage the clutch when the clutch pedal is depressed and released. The release bearing disconnects the engine from the transmission by pushing the clutch release fork or lever to separate the clutch pressure plate from the clutch disc.

 Clutch release bearing structure and working principle

1. Structure:

   - Bearing: The release bearing is usually a ball bearing or needle bearing mounted in a metal housing.

   - Piston or push rod: The bearing is connected to the slave cylinder by a piston or push rod.

   - Release Fork or Lever: The bearing pushes the release fork or lever, and these parts in turn push the clutch pressure plate.

2. Principle of operation of the clutch release bearing:

   - Depressing the clutch pedal: When the driver depresses the clutch pedal, the master cylinder generates hydraulic pressure, which is transmitted to the slave cylinder through the hydraulic line.

   - Slave cylinder action: the piston in the slave cylinder is pushed by the hydraulic pressure and moves forward, driving the release bearing.

   - The release bearing pushes the release fork: the release bearing moves forward and pushes the release fork or lever to separate the clutch pressure plate from the clutch disc.

   - Clutch Disengagement: When the clutch pressure plate separates from the clutch disc, the connection between the engine and the transmission is broken, allowing the driver to perform a gear shift operation.

   - Release Clutch Pedal: When the driver releases the clutch pedal, the hydraulic system retracts, the release bearing returns to its original position, the clutch pressure plate represses the clutch disc, and the connection between the engine and transmission is restored.

 Clutch release bearing function and role

1. Engaging and disengaging: the main function of the release bearing is to help engage and disengage the clutch when the clutch pedal is pressed down and released, ensuring smooth gearshift operation.

2. Reducing friction: the release bearing extends the service life of the clutch system by reducing the friction between the clutch pressure plate and release fork.

3. Transmitting mechanical force: the release bearing converts the hydraulic energy generated by the slave cylinder into mechanical force, which pushes the release fork or lever to achieve clutch disengagement and engagement.

 Common faults and causes of clutch release bearing

1. Normal wear:

   - Cause: Wear caused by long-term use.

   - Impact: The internal friction of the bearing increases, generating noise and vibration, and eventually leading to bearing failure.

2. Poor lubrication:

   - Cause: Lack of lubrication or poor lubrication.

   - Effects: Increased friction inside the bearing, accelerated wear, possible overheating and seizing. 

3. Improper operation:

   - CAUSE: Improper operation by the driver, such as depressing or releasing the clutch too hard, too violently, or frequent half linkage operations.

   - Effect: Additional impact and wear accelerate bearing damage.

4. Improper installation:

   - CAUSE: The release bearing is not installed correctly, e.g. excessive clearance with the pressure plate or clutch housing, loose bearing seat, etc.

   - Impact: The bearing shakes and becomes unstable during operation, accelerating wear and damage.

5. Quality problem:

   - Cause: Poor manufacturing quality of bearings, such as poor materials, insufficient machining accuracy, etc.

   - Impact: bearings are prone to failure in the process of use.

6. Environmental factors:

   - Cause: Dust, dirt and moisture and other impurities in the working environment enter into the internal bearing.

   - Influence: Increase friction and wear, and even lead to bearing seizure or failure.

7. Improper clutch adjustment:

   - CAUSE: Improper clutch adjustment, resulting in the release bearing not being able to completely disengage the clutch.

   - EFFECT: Premature wear or failure.

8. Worn clutch discs:

   - CAUSE: Worn clutch discs cause the release bearing to work harder.

   - EFFECT: Increased friction and wear on the bearing.

9. Overheating:

   - CAUSE: Prolonged clutch slip generates heat.

   - Effect: Reduced lubrication of the bearing and accelerated wear.

10. extreme temperatures:

    - Cause: Extreme heat generated during heavy use.

    - Effect: Shortens the service life of the bearing.

 How to judge whether the release bearing is damaged

1. Listen to the sound:

   - Method: When the engine is started and the clutch pedal is pressed lightly, if a ‘rustling’ or ‘squeaking’ sound is heard at the end of the freewheeling stroke, and the sound disappears when the pedal is pressed further down, then it is likely to be a release bearing problem. If the sound persists, especially when in gear, it is usually a sign of a damaged release bearing. 

2. Check the noise:

   - Method: When the vehicle is idling, press the clutch pedal lightly. If a distinct friction sound is heard, the sound of releasing the pedal disappears, and the sound reappears when the pedal is pressed lightly again, this is an indication that the release bearing may be worn or damaged.

3. Operation feeling:

   - Method: If you feel difficulty in shifting gears while driving, or if the clutch pedal feels abnormal, it may also be a release bearing problem.

4. Check for stalling:

   - Method: During vehicle maintenance, you can manually check whether the release bearing can rotate smoothly and whether there is any hysteresis.

 Clutch release bearing preventive measures

1. Reasonably adjust the clutch clearance:

   - Method: Reasonably adjust the clutch free stroke and release clearance according to the provisions of the vehicle technical documents to avoid excessive free stroke or too small free stroke.

2. Manoeuvre the clutch correctly:

   - Method: Follow the operation principle of ‘fast pedal, slow release’, avoid long time half linkage or excessive use of the clutch.

3. Regular maintenance and repair:

   - Method: Regularly check the clutch system, including checking the wear of the clutch, replacing worn parts, cleaning and lubricating the release bearing.

4. Pay attention to driving habits:

   - Methods: Avoid bad driving habits such as slamming on the clutch pedal or changing gears frequently.

5. Professional maintenance:

   - Method: When carrying out clutch system maintenance, it is better to be operated by professional technicians to ensure correct installation and avoid early damage caused by improper installation.

Through these measures, the service life of the clutch release bearing can be effectively extended, reducing unnecessary maintenance costs and driving risks.