Here will mainly describe the mechanical friction type main clutch and the overhead winch system friction clutch fault and maintenance. Engineering machinery used in the main clutch are mechanical friction type, medium and small machinery horsepower mostly monolithic or double clutch, large horsepower powder metallurgy materials engineering machinery commonly used with high friction coefficient, large tablet is the multi disc wet clutch. The friction clutch is divided into two types: regular joint type and non regular type, according to different pressure conditions. The former is used for medium and small horsepower mobile engineering cranes, and the latter is used for larger crawler chassis cranes.1. clutch skid, when the vehicle resistance increases, the speed decreased significantly, while the engine speed has declined little, that is, the clutch slip.The 2. clutch shaking when the clutch according to the normal operation smoothly engage, the vehicle is not gradually and smoothly increase speed, and make the vehicle even intermittent start, jitter, until the clutch is completely combined with the site known as the clutch. The clutch shake causes the driver uncomfortable, and will cause the transmission system parts to accelerate wear because of the impact load.3., clutch separation is not complete, clutch separation is not complete, refers to the clutch lever or pedal in the separation position, the active disk and the driven disk is not completely separated, there is still some power transmission.Clutch separation is not complete, will make the transmission gear difficult, produce tooth impact, damage tooth end; also accelerate the pressure plate and friction plate surface wear, cause clutch heating.4. clutch abnormal sound clutch, abnormal sound occurs in clutch engagement or separation process, and the speed changes. Because the noise is caused by abnormal friction or collision between the parts, it is generally clearer. Such as clutch just when combined, sometimes there will be "sand", "sand" sound, combined with, or separation, or sudden change in speed, there will be "grams", "grams" of the sound, etc..