Clutch Release Bearing, also often referred to as Clutch throwout bearings or Clutch Slave Cylinder, is an important component in a car's manual transmission. Its main function is to release the pressure between the clutch pressure plate and the flywheel when the clutch pedal is pressed down, causing the clutch disc to separate from the flywheel, thus cutting off the power transfer between the engine and the transmission and making it possible to shift gears.

The clutch release bearing is usually located between the clutch pressure plate and the transmission input shaft. When the driver depresses the clutch pedal, the clutch release bearing moves forward along the input shaft, pushing the pressure plate and separating it from the flywheel.

To check whether the clutch release bearing is out of oil or worn, you can follow the steps below:

1.Listen to the sound: 

In the idle state of the engine, first step down the clutch pedal, if you hear ‘rustling’ or ‘clattering’ sound, and then lift the pedal sound disappeared, and then step down the clutch pedal again to make the release bearing contact with the release lever, if the friction sound appears again, this usually indicates that the release bearing is out of oil or worn out. If the friction sound reappears, this usually indicates that the release bearing may be out of oil or worn out. 

2. Check free travel: 

Check the free travel of the clutch pedal. If there is too little or no free travel, it may mean that the release bearing is constantly under stress, which may be due to reduced clearance as a result of wear.

3. Dismantle for inspection:

   - It is necessary to raise the vehicle and remove the transmission guard.

   - Release the clutch pedal and remove the retainer on the clutch pedal shaft in order to release pedal pressure.

   - Remove the clutch cover and pressure plate, followed by the release lever.

   - Carefully pull out the release bearing from the release bearing housing using a special tool or puller.

4. Visual inspection:

   - Inspect the release bearing surface for signs of corrosion, scoring or wear.

   - Measure the wear of the inner seat ring, if the wear exceeds 0.3mm, it needs to be replaced.

   - Confirm that the bearing can rotate smoothly and there is no stagnation.

5. Lubrication:

   - Check bearings for grease. Bearings that are starved of oil are usually dry or have run out of grease.

   - Note that if the bearings are pre-lubricated and enclosed, additional lubricant is not normally required, but it is necessary to verify that the seals are intact.

6. Reassembly:

   - If wear or lack of grease is observed, the release bearing should be replaced and an appropriate amount of molybdenum disulphide lithium grease applied to the designated location in the bearing housing prior to installation, taking care not to overdo it so as not to contaminate the follower disc.

   - When reassembling ensure that all parts are correctly installed and restore the original fit clearance.

By following these steps, the condition of the release bearing can be effectively determined and appropriate repair action taken. If unsure of how to proceed, it is advisable to seek the assistance of a professional mechanic to avoid further damage to other clutch components.

When does the release bearing grease need to be replenished?

Grease replenishment of the release bearing is not normally a routine routine maintenance task as the release bearing is normally sealed and inside the clutch assembly and cannot be easily lubricated directly. However, poor lubrication or the need for replacement may be indicated when the release bearing exhibits the following conditions

1. Abnormal Noise: If a noticeable noise is heard when the clutch is operated, this may be due to dry grinding or wear caused by insufficient lubrication inside the bearing.

2. Difficulty in operation: If the clutch pedal feels heavier than usual or shifting gears becomes difficult, this may be due to a worn release bearing with poor lubrication affecting its smooth operation.

3. Signs of wear: If the release bearing is worn or rusted when disassembled and inspected during vehicle maintenance, this is an indication that the original lubrication has failed.

4. Vehicle Starting Shake: If the vehicle feels unusually shaky when starting, this may be related to the lubrication of the clutch system, including the release bearing.

In practice, release bearing lubrication is usually handled in conjunction with the replacement of the clutch assembly, rather than being greased separately. Because release bearing replacement usually involves the replacement of the clutch pressure and slave discs, the new release bearing is inspected and replaced at this time, and it is ensured that the new bearing carries adequate lubrication. For the layman, this is not a process to replenish the grease on your own, but should be done by a professional mechanic during maintenance or replacement.

If you experience any of these problems, it is recommended that you take your vehicle to a specialist workshop where a technician can assess the need for a release bearing replacement, as well as the maintenance of the entire clutch system. Automatic lubrication systems may be used in some advanced or specific design vehicles, but this is not universal.