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The BMW 750i sedan matches the ZF 6HP26 automatic transmission with a torque converter of 000193. The hydraulic torque converter of the vehicle once flooded, causing the vehicle to shake when it was running at 6080 km/h, so it was sent to our factory for remanufacturing of torque converter. After cutting, it was found that the friction material on the friction disc of the hydraulic torque converter was lost because of water corrosion, so we replaced the new original friction plate, O - shaped seal and lip oil seal. Install the test car, troubleshooting. Unfortunately, in less than 1 months, the phenomenon of dithering occurred again at 60~80 km/h. Inspection and analysis: after analysis, the jitter of the vehicle should be caused by hydraulic torque converter locking and trembling, so the following routine steps should be taken for inspection. Connection diagnostic instrument, no fault code. Check data flow, lock clutch clutch oil pressure normal. The vacuum test method is used to check the vacuum degree of the lock control valve, which is in line with the standard. The electronic control system is tested, and the valve body test and the electromagnetic valve test are normal. Once again, the dynamic balance test of torque converter is achieved. Check the automatic transmission oil level to achieve the original target. It is normal to check the other aspects of the engine. The above inspection does not find abnormal phenomena, but the input and output axis speed of the torque converter in the data flow is observed, and the locking clutch is unlocked, that is to say, the lock clutch has been between skidding and non skidding, which is the direct cause of the jitter. After cutting the hydraulic torque converter again, it was found that the outer edge of the original friction disc had been burned and blackened. According to the relationship between the friction coefficient of the locking clutch and the slip, it is judged that this should be a fault caused by the incorrect friction coefficient of the locking clutch. Figure 2 shows the relationship between the friction coefficient and slip speed of the 3 different locking clutches. During the locking process of clutch A and B, the friction coefficient decreases with the decrease of slip difference, so it does not cause the lock to tremble. The friction coefficient of the clutch C increases with the decrease of the slipping degree, which causes the lock to tremble. However, this process does not trigger a fault code. The friction characteristics of the locking clutch are related to friction plates, steel plates and pressure plates. Because the friction plates previously replaced are original products, there should be no problem. So we examined the other parts of the torque converter, and finally found that the lock clutch pressure plate, the steel plate and the front cover friction plate have been worn as smooth as the mirror surface, which makes the friction characteristics of the torque converter lock clutch change. Friction coefficient is related to surface roughness, so increasing surface roughness is the only solution. Troubleshooting: the irregular imprint of the steel sheet, press plate and front cover contact with the friction plate is made, and the friction coefficient between the friction plates is increased, and the related test and loading test are carried out after welding. The problem is solved. Review and conclusion: the reason why the outer edge of the friction plate is blackened is that the outside of the friction disc is the first contact and the first one to be heated during the locking process. The locking clutch of the hydraulic torque converter of the vehicle has been in the state of skidding and non skidding, and also caused the blackening of the outer edge of the friction disc. Before analyzing the whole process of maintenance, we can find that the remanufacture of the torque converter is a seemingly simple but very complicated process. It is difficult from the selection of the friction material to the maintenance of the parts and the judgment of the fault point. The above method is only a solution in the maintenance process, and it may not be widely used in Remanufacturing of torque converter. Because remanufacturing is standard, and although we have solved the problem according to this method, there is no way to determine how much friction coefficient is added because there is no related equipment to test. But the essence of this method is to increase the friction coefficient and make the torque converter reach the standard torque transfer efficiency, which is the only indicator to measure the remanufacturing effect of the torque converter, which is worthy of reference. In addition, the case can also be explained that torque transmission efficiency testing should be a standard item for torque converter remanufacturing.