The so-called release bearing refers to the bearing used between the clutch and the transmission, usually referred to as the "clutch release bearing". When stepping on the clutch, if the fork is combined with the high-speed rotating clutch pressure plate, a bearing must be needed to eliminate the heat and resistance generated by direct friction. Therefore, the bearing installed in this position is called a release bearing. The release bearing pushes the pressure plate to separate it from the friction plate, thereby cutting off the power output from the crankshaft.

Performance requirements for clutch release bearings:

The separation bearing should move flexibly without sharp noise or jamming, and its axial clearance should not exceed 0.60mm. The wear of the inner race should not exceed 0.30mm.

The working principle and function of the clutch release bearing:

The so-called clutch, as the name suggests, refers to the use of "separation" and "combination" to transmit an appropriate amount of power. The engine is always rotating, while the wheels are not. To stop the vehicle without damaging the engine, the wheels need to be disconnected from the engine in some way. The clutch allows us to easily connect a rotating engine to a non rotating transmission by controlling the slip between the engine and the transmission.

The clutch release bearing is installed between the clutch and the transmission, and the release bearing seat is loosely sleeved on the tubular extension of the first shaft bearing cover of the transmission. Through the return spring, the shoulder of the release bearing is always pressed against the release fork and retracted to the final position, maintaining a gap of about 3-4 mm with the end of the release lever (release finger).

Due to the synchronous operation of the clutch pressure plate, release lever, and engine crankshaft, while the release fork can only move along the axial direction of the clutch output shaft, it is obviously not feasible to directly use the release fork to shift the release lever. By using the release bearing, the release lever can rotate while moving along the axial direction of the clutch output shaft, ensuring smooth engagement and gentle separation of the clutch, reducing wear, and extending the service life of the clutch and the entire transmission system.

Key points to note when using clutch release bearings:

1. According to the operating regulations, avoid the clutch from being in a semi engaged and semi disengaged state, and reduce the number of clutch uses.

2. Pay attention to maintenance, regularly or during annual inspection and maintenance, soak the butter thoroughly with steaming method to ensure it has sufficient lubricant.

3. Pay attention to leveling the clutch release lever to ensure that the elasticity of the return spring meets the regulations.

4. Adjust the free stroke to meet the requirements (30-40mm) to prevent excessive or insufficient free stroke.

5. Try to minimize the number of joints and separations, and reduce impact loads.

6. Gently step on it, making it smoothly engage and detach.     

Common factors causing damage to clutch release bearings during use:

1. Working conditions and forces on clutch release bearings

The release bearing is subjected to axial load, impact load, and radial centrifugal force during high-speed rotation during use. In addition, due to the fact that the thrust of the fork and the reaction force of the release lever are not in the same line, a torsional moment is also formed. The working conditions of the clutch release bearing are poor, intermittently rotating at high speeds and enduring high-speed friction, with high temperatures, poor lubrication conditions, and no cooling conditions.

2. Reasons for damage to clutch release bearing

The damage of the clutch release bearing is closely related to the driver's operation, maintenance, and adjustment. The reasons for the damage are generally as follows:

1) Excessive working temperature leads to overheating

Many drivers often half step on the clutch when turning or decelerating, and some even put their feet on the clutch pedal after shifting; Some vehicles have excessive adjustment of free travel, resulting in incomplete clutch separation and being in a semi engaged and semi disengaged state. This state causes dry friction and generates a large amount of heat to be transmitted to the release bearing. The shaft bears heat to a certain temperature, and the butter melts or dilutes and flows, further increasing the temperature of the release bearing. When the temperature reaches a certain level, it burns out.

2) Wear due to lack of lubricating oil

The clutch release bearing is lubricated with grease, and there are two methods to add grease. For the 360111 release bearing, the rear cover of the bearing should be opened and filled with grease during maintenance or when removing the transmission, and then the rear cover should be reinstalled; For the 788611K release bearing, it can be disassembled and placed in molten lubricating grease for soaking, cooled, and then removed to achieve lubrication. In practical work, drivers tend to overlook this, resulting in a lack of oil in the clutch release bearing. The wear amount of the separation bearing in the absence of lubrication or with little lubrication is often several to several tens of times that of the lubricated wear amount. As wear increases, the temperature will also increase significantly, making it more susceptible to damage.

3) Free travel is too small or loaded too many times

According to the requirements, a clearance of 2.5mm is generally suitable between the clutch release bearing and the release lever, which is reflected in the free stroke of 30-40mm on the clutch pedal. If the free stroke is too small or there is no free stroke at all, it will cause the release lever and release bearing to be in a normal engagement state. According to the principle of fatigue damage, the longer the working time of the bearing, the more severe the damage situation; The more times the bearing is loaded, the easier it is for the release bearing to undergo fatigue failure. Moreover, the longer the working time, the higher the temperature of the bearing, which is more likely to burn out and reduce the service life of the separation bearing.

4) In addition to the above three reasons, whether the release lever is adjusted smoothly and whether the return spring of the release bearing is in good condition also has a significant impact on the damage of the release bearing.

Maintenance of clutch release bearing:

Fix the inner ring of the release bearing by hand, rotate the outer ring, and apply pressure axially. If there is any obstruction or obvious clearance, the release bearing should be replaced. The release bearing is usually lubricated once. Do not disassemble and clean at will during maintenance. If there is dirt, clean the surface with a clean cloth. As shown in the figure.

The Phenomenon and Common Causes of Burnt and Damaged Clutch Release Bearings

Like a Dongfeng agricultural vehicle, when the clutch pedal is pressed, the engine is difficult to start. Using a hand crank to rotate the crankshaft feels very heavy, and releasing the clutch pedal to shift into neutral can smoothly start the engine. When the engine is idling, as long as the clutch pedal is pressed, the engine will immediately shut down.

Stop and check the engine, press the clutch pedal, move the driven plate, and the driven plate can rotate freely without any damage to other components. Move the clutch release bearing and it is found that the release bearing cannot be moved. After disassembly and inspection, it was found that the release bearing was burned due to poor lubrication, and its inner and outer rings, retainer, and other parts were severely burned and locked. During operation, the bearing not only failed to rotate, but also caused significant friction and abnormal noise between the clutch release lever, resulting in difficulty in starting the engine.

Common causes of damage to the release bearing include:

1. Although the release bearing was filled with lubricating grease when leaving the factory, after prolonged use, especially when encountering high temperatures, the lubricating grease dissolves and is gradually thrown out during bearing operation. The bearing experiences dry friction and generates heat, leading to erosion, stagnation, and loss of separation effect.

2. Some drivers are accustomed to using a half foot clutch, causing the clutch to be in a semi engaged and semi disengaged state, causing dry friction of the clutch and heat transfer to the release bearing, causing the lubricating grease in the bearing to become thin and lose. When the temperature reaches a certain value, the bearing is burned and damaged.

3. During vehicle maintenance, missing or missing small oil bottoms can cause mud to invade the separation bearing and cause bearing wear.

4. The free stroke of the clutch pedal is too small or absent, causing it to be in a state of frequent engagement, causing fatigue damage or even ablation; Excessive pedal travel causes incomplete clutch separation and difficulty in shifting. The clutch is in a semi engaged and semi disengaged state, generating dry friction and heat transfer to the release bearing, causing the lubricating grease to flow out and the bearing to burn out.

5. After the separation shaft is subjected to dust erosion, the lubricating grease deteriorates, exacerbating its damage.

6. The separation bearing and separation sleeve have poor fit, especially when the clearance between the two is too large, loose, and not in the same plane. During operation, the separation shaft bears impact load, causing track wear and erosion.

The release bearing should rotate flexibly without any abnormal noise, and the axial clearance should exceed the standard deviation of 0.6mm. The wear of the inner race should not exceed 0.3mm, otherwise it should be replaced with a new one. The fit clearance between the pedal shaft and the release fork and the bushing is too large, and the bushing should generally be replaced and trimmed for fit. When cutting two bushings on the bracket, a long blade knife or a larger knife with a guide device must be used to ensure their coaxiality.

When the engine is idling and the clutch pedal is pressed, if a sound of "sand, sand" or "clatter" is heard, the sound disappears after lifting the clutch pedal, and then a slight friction sound (causing the release bearing to come into contact with the release lever) reappears, indicating that the clutch release bearing is out of oil or worn

When disassembling and inspecting the release bearing, first unscrew the fixing screws and bolts of the release lever from the transmission housing, remove the release lever, remove the release bearing component and fixing spring, and then use a puller to pull the release bearing off the release bearing seat. Check the release bearing. If there is a shortage of oil, it should be replenished. If it is worn, it should be replaced. When assembling the release bearing, apply an appropriate amount of molybdenum disulfide lithium based grease to the position indicated by the arrow on the release bearing seat, and the amount should not be too much to avoid polluting the driven plate.

The separation bearing generally adopts axial thrust ball bearing, which is pressed onto the separation sleeve. It is regularly filled with lubricating grease or engine oil through a specially designed nozzle installed on the flywheel housing to lubricate the working surface of the separation sleeve and the separation bearing. Some separation bearings use pre lubricated bearings with good sealing, and it is not allowed to clean them with gasoline or add lubricant during disassembly and assembly, as long as they are wiped clean.