Symptom diagnosis: When the 6×4 car is under heavy load, especially when driving bumps, it occasionally makes a knocking sound. Pay attention to check whether the balance shaft of the middle and rear axle is displaced and interferes with the transmission shaft.If the noise increases with the speed of the car, and there is jitter, this is generally caused by the loss of balance of the transmission shaft.This kind of vibration is noticeable in the cab.The unbalance of the dynamic balance of the drive shaft should be less than 100g.cm.

　　A serious failure of the dynamic balance of the drive shaft will cause damage to related components.The common ones are the clutch shell cracks and the fatigue damage of the middle rubber support.

　　Tighten the front wheel of the car with mats, jack up the middle and rear drive axles on one side of the car; start the engine, put it in high gear, and observe the vibration of the drive shaft.During the observation, notice that when the speed drops, if the shimmy increases significantly, it indicates that the drive shaft is bent or the flange is skewed.

　　The bending of the transmission shaft is the bending of the shaft tube, most of which are caused by the overload of the car.Due to overloading and overhanging of coal-carrying vehicles, more failures occurred due to bending and breaking of drive shafts.If some trucks and trailers transport more than 60 tons of coal, the drive shaft is seriously damaged due to overloading and overhanging.Although the intermediate support of the transmission shaft was strengthened and the strength of the flange fork was strengthened, the failure of fracture and damage still occurred.

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