What causes the clutch to sink and make it difficult to shift gears after a traffic jam?
Have you ever encountered this situation when driving a manual transmission car:
1. The clutch suddenly becomes very heavy. Not only is it difficult to step on, but the coupling and separation points of the clutch are particularly blurry;
2. It is easy to have difficulty in shifting gears after a traffic jam or a long period of semi-linkage.
If so, then the clutch pressure plate is likely "rotted". The only way to solve the problem at this time is to replace the clutch pressure plate.
What is "Clutch Pressure Plate Failure"?
We need to start with the structure of the clutch
The pressure plate is an important part of the manual transmission clutch. It has a diaphragm spring on it, which is responsible for the separation and engagement of the clutch. The picture above is a schematic structural diagram of a manual clutch. The red part is the flywheel and pressure plate. The flywheel is connected to the engine crankshaft, and the pressure plate is fixed on the flywheel with screws. When the engine starts, the flywheel and pressure plate rotate. The green part is the clutch plate and transmission input shaft. The flywheel and pressure plate clamp the clutch plate in the middle, transmitting power to the clutch plate through friction, and the clutch plate transmits power to the transmission through the transmission input shaft. As shown in the picture above, it is a diaphragm spring. The diaphragm spring provides the elastic force that causes the pressure plate to press the clutch plate tightly against the flywheel. When we depress the clutch, the diaphragm spring springs up, the pressure plate releases the pressure on the clutch plate, and power transmission is interrupted. The lowering of the pressure plate is actually the lowering of the diaphragm spring. The diaphragm spring of the pressure plate is made of steel. When the clutch is depressed, the diaphragm spring uses the fixed pin as a fulcrum to form a lever structure. The clutch fork pushes against the release bearing, depressing one end of the diaphragm spring. At this time, the other end of the diaphragm spring begins to lift under the action of the lever force, and the pressing force of the friction plate on the clutch plate decreases. Because of the longer lever arm on one side of the release bearing, the clutch pedal will be particularly light.
In addition, the diaphragm spring is stamped from a whole steel plate as a whole. After being installed on the pressure plate, there is a large internal stress between the diaphragm springs. When the clutch is depressed to a certain extent, the internal stress of the diaphragm spring and the release bearing can easily fully spring up under pressure, and at this time the clutch is completely separated. This is why we have an obvious sense of separation and integration when we step on the clutch. If the clutch is used normally, this characteristic of the pressure plate diaphragm spring will remain good until the clutch plate wears to the limit, and the clutch pedal will not become significantly heavier. But in reality, there may be various problems that cause the clutch to overheat, and the most heat-resistant clutch is the clutch plate and diaphragm spring. The clutch plate may be burned out due to overheating, and the diaphragm spring may be burned out and lose its rigidity due to overheating. After the diaphragm spring is burned out, its hardness and rigidity will decrease. When the clutch is depressed at this time, the diaphragm spring will be deformed due to insufficient rigidity, and the other end cannot be lifted normally to release the pressure. When the diaphragm spring flexes, the lever's moment arm becomes shorter and more force is required to pop the other end of the diaphragm spring, so the pedal becomes heavier.
And because the deformation of the diaphragm spring acts as a buffer, the clutch disengagement action also becomes particularly blurry. After the diaphragm spring is burned out, the clutch can barely work because the diaphragm spring still has a certain rigidity when the car is cold. At this time, the clutch pedal is heavier, but as long as you press hard, the clutch can still be completely disengaged. So at this time, I just step on it a little harder, but there is no problem with separation. When the clutch is in a traffic jam state for a long time, the temperature of the clutch rises rapidly due to frequent semi-linkage. At this time, the temperature of the diaphragm spring increases, the stiffness further decreases, and incomplete separation is prone to occur. The specific performance is gear meshing. difficulty. At this time, even if the clutch is pressed to the bottom, the diaphragm spring is not rigid enough to completely separate from the pressure plate. The only solution when this happens is to replace the clutch pressure plate.
Moreover, the annealing of the pressure plate is generally caused by poor rotation of the release bearing, so if it needs to be replaced, at least the release bearing must be replaced together, otherwise the new pressure plate will be damaged again within a few days.