The clutch release bearing is the bearing used between the clutch and the transmission.
When the clutch pedal is depressed, the release fork must engage with the clutch pressure plate, which is rotating at high speed. A bearing is essential here to reduce the heat and resistance that would result from direct friction. The bearing installed in this position is therefore called the release bearing.
The release bearing pushes against the pressure plate, causing it to disengage from the friction disc. This disengages the power from the crankshaft.
Common Failure Symptoms
1. Abnormal Noises
Grinding or squeaking when depressing the clutch: Caused by worn bearing balls/needles or depleted lubricant.
Persistent metal scraping: Indicates a fractured bearing cage or seized rolling elements.
2. Clutch Pedal Issues
Heavy/sticking pedal: A damaged bearing increases sliding resistance, hindering fork movement.
Pedal vibration: Results from imbalanced bearing rotation or uneven pressure plate wear.
3. Gear Shifting Difficulties
Gear grinding or incomplete disengagement: Bearing failure prevents full pressure plate separation, failing to cut off crankshaft power.
Root Causes of Failure
Extended load exposure --> Temperature surge --> Grease degradation --> Metallurgical weakening --> Accelerated fatigue cracks --> Catastrophic bearing failure
1. Overheating due to excessive operating temperature
Many drivers often partially depress the clutch pedal when turning or decelerating, and some keep their foot on the clutch pedal after shifting gears; excessive adjustment of the free travel in some vehicles prevents the clutch from disengaging completely, leaving it in a semi-engaged, semi-disengaged state. This condition causes dry friction, generating a large amount of heat that is transferred to the release bearing. When the bearing heats up to a certain temperature, the grease melts or thins and flows away, causing the temperature of the release bearing to rise further and burn out.
2. Wear Due to Insufficient Lubrication
Clutch release bearings are lubricated with grease. Two lubrication methods exist:
For 360111 bearings, remove the rear cover during maintenance or transmission removal, pack with grease, and reassemble.
For 788611K bearings, remove and immerse in molten grease until saturated, then cool before reinstallation.
Drivers often neglect this lubrication, causing grease starvation. Wear rates under insufficient lubrication are typically several to dozens of times higher than under proper lubrication. Increased wear generates substantially higher temperatures, accelerating failure.
3. Excessive Load Cycles or Insufficient Free Travel
The specified clearance between the release bearing and release fork is typically 2.5 mm, corresponding to 30-40 mm of free travel at the clutch pedal. Insufficient or zero free travel forces the release fork and bearing into constant contact. According to fatigue failure principles:
Longer operating times exponentially increase damage severity.
Higher load cycles promote fatigue failure.
Prolonged operation also elevates bearing temperature, increasing burnout risk and significantly reducing bearing service life.
Type
Mechanical Release Bearing
Structural Features: Transmits pedal force mechanically via cable/lever, with the bearing making direct contact with the metal release fork.
Hydraulic Release Bearing
Integrated Structure: Features a unified design integrating the bearing with the hydraulic slave cylinder, utilizing a built-in piston to actuate the bearing's movement.
