A Yutong Bus with a mileage of about 44 thousand km. The driver reflected that when the vehicle was running at a speed of 70 km/h to 80 km/h, the car generated vibration and produced noise. Fault diagnosis: after the first test, vibration and noise begin to appear when the speed reaches 40 km/h, and the noise is gradually increased with the increase of speed, and the vibration and noise are a little stronger in the middle and rear passenger areas of the vehicle. The vibration and noise are weakened when the speed is over 80 km/h. The car has been repaired many times in other repair plants, and has not been able to solve the problem. The vehicle's suspension system and transmission system are carefully inspected according to the description of the driver and the situation felt during the road test. No loosening, abrasion, aging or lubrication is not in place. The new welding balance block is found on the front and back two sections of the transmission shaft, which is welded on the dynamic balance of the transmission shaft. The noise and vibration of the transmission shaft are slightly better after the transmission shaft is balanced, but it is still obvious. After careful analysis of the failure phenomenon during the trial run, it is considered that noise and vibration are indeed like a moving component losing balance, which may be damaged by transmission shaft. In order to ensure the correction quality, the transmission shaft will be sent to the manufacturer to be corrected according to the factory inspection standard. After adjusting the transmission shaft to carry out the road test, it is found that the fault is still at fault. In the road test, it is impossible to directly observe the operation of the transmission shaft, and decide to stop the car on the ditch, use the triangle wooden plug to stop the 2 front wheels, prevent the vehicle from moving in the test, and use the lifting equipment to lift the 2 rear wheels to leave the ground, arrange the driver to simulate the normal running state of the vehicle, and control the speed of the vehicle to the maximum noise and vibration. Within the range of the value. When the drive shaft is observed at the bottom of the car, it is found that the transmission shaft begins to shake when it reaches a certain speed. It slowly produces noise and vibration, indicating that our maintenance ideas and the trouble spots found are no problem. The balance of the transmission shaft has been corrected by the manufacturer according to the factory standard. What causes the shaft to shake? Again, check the transmission shaft and the related parts before and after. It is found that the angle of the 2 cross axis of the rear shaft is larger than that of the transmission shaft, and the angle deviation of the transmission shaft will not cause noise and vibration. Referring to relevant information, it is known that the smaller the angle of the transmission shaft of the cross rigid rigid universal joint, the more stable the operation is. Compared with the same type of vehicle, it is found that the angle of the transmission shaft is too large. It is decided to change the angle of the transmission shaft to be tested, to remove the fixed bolt of the middle support of the transmission shaft, to replace the lengthened bolt, and to install the cushion between the middle support and the beam in the middle of the transmission shaft, so that the middle support will move down and the angle of the rear moving shaft is reduced. But attention, at this time, we should consider the angle of the cross shaft of the front drive shaft, take a more reasonable position, and it can be tested by adding and subtraction of the gasket to determine the reduction of the gasket. When the adjusting gasket is reduced to a thickness of 2 cm, it is found that the transmission shaft is no longer jitter or noise.