For example, when starting a Dongfeng agricultural vehicle, the engine is difficult to start when the clutch pedal is depressed. When turning the crankshaft by hand, it feels very heavy. Only when the clutch pedal is released and the neutral gear is engaged can the engine be started smoothly. When the engine is idling, as long as the clutch pedal is depressed, the engine immediately stalls. When checking the stall, pressing the clutch pedal and moving the driven plate, the driven plate can rotate freely and other components are not damaged. When moving the automotive bearing, it is found that the separation bearing cannot be moved. After disassembly and inspection, it was found that the separation bearing was burned due to poor lubrication, and its inner and outer rings and retainer were severely burned and locked up. The bearing not only cannot rotate during operation, but also produces significant friction and noise between the separation lever and the clutch separation, causing difficulties in starting the engine.
Although the clutch bearings are already filled with grease when it leaves the factory, after long-term use, especially after encountering high temperatures, the grease will melt and be gradually thrown out during bearing operation. This will cause dry friction and heat generation, leading to burnout and locking, and loss of separation function.
Some drivers have the habit of using half-clutch, which keeps the clutch in a half-engaged, half-separated state, causing dry friction on the clutch, transferring heat to the separation bearing, causing the grease inside the bearing to become thin and flow away. When the temperature reaches a certain value, the bearing will burn out.
During vehicle maintenance, if the oil pan is missing or not installed, mud and dirt can invade the separation bearing, causing wear and tear.
If the free travel of the clutch pedal is too small or non-existent, it will be in a state of frequent engagement, which will cause fatigue damage or even burnout. If the pedal travel is too large, it will cause incomplete clutch separation and difficult to shift, and the clutch will be in a state of half-engagement and half-separation, producing dry friction. The heat will be transferred to the separation bearing, causing the grease to flow out and the bearing to burn out.
After the separation bearing is eroded by dust, the grease will deteriorate and accelerate its wear and tear.
If the clutch bearing is not well coordinated with the separation sleeve, especially if the clearance between the two is too large and not in the same plane, the separation bearing will be subjected to impact load during operation, causing track wear and burnout. The separation bearing should rotate flexibly without abnormal noise. The wear of the inner race should not exceed 0.3mm, otherwise it should be replaced with a new part. If the clearance between the pedal shaft, the separation fork shaft and the bushing is too large, the bushing should be replaced and re-machined to fit.
When the engine is idling, if a "rustling" or "clattering" sound is heard when the clutch pedal is depressed and the sound disappears when the clutch pedal is lifted, and if friction sound is heard again when the separation bearing and separation lever are slightly contacted, it means that the clutch separation bearing is short of oil or worn. When disassembling the separation bearing, first unscrew the separation lever fixing screws and bolts from the automatic transmission with clutch pedal case, remove the separation lever, remove the separation bearing assembly and the fixing spring, and then use a puller to pull the separation bearing from the separation bearing seat. Check the separation bearing. If it is short of oil, it should be replenished. If it is worn out, it should be replaced. When assembling the separation bearing, apply an appropriate amount of lithium molybdenum disulfide-based grease to the arrow on the separation bearing seat. The amount should not be too much to avoid polluting the driven plate.
Separation bearings generally use axially thrust ball bearings, which are pressed on the separation sleeve and are periodically lubricated with grease or engine oil through an oil nozzle special set on the flywheel casing to lubricate the working surface of the separation sleeve and separation bearing. Some automobile bearings have well-enclosed pre-lubricated bearings, which should not be cleaned with gasoline during disassembly and assembly and do not require the addition of lubricants, but only need to be wiped clean.