The mileage is about 190 thousand km, with 272 engines and 722.9 transmission Benz S350 cars. When the vehicle runs at low speed or at high speed, the steering wheel is abnormal jitter, 100km/h is the most obvious. It has been two months since the replacement of tires, dynamic balance and four wheel alignment. Fault diagnosis: verify the fault phenomenon, test the car with the customer after the car, the low speed 50 to 80km/h steering wheel light jitter, the speed reaches 100km/h when the jitter is more obvious, the speed is high when the jitter gradually reduced, and the occasional jitter when 120 to 130km/h will occasionally appear jitter. The tire dynamic balance is not good. The wheel hub deformation, the tire aging, the wear poor, the chassis support ball head wear loose open first check the vehicle chassis suspension arm ball head, not found the ball head arm has the wear loose phenomenon, no abnormal. Check tyre wear. During the third week of 2014, tires wear no aging, and tires are normal. Turn the wheel to inspect the hub. The four wheel hub has no obvious deformation in visual inspection. Communicate with the customer to make a dynamic balance check, remove the tire from the car, balance the balance test on the balance machine, and the balance data of the four wheel tire are all normal, and the maximum difference is 5g. This data almost does not affect the steering wheel current jitter. The wheel hub is normal, the suspension arm ball head is normal, the tire pressure is calibrated, and the tire is fitted. Again test the car, the failure is still. It was doubted that the quality of the car's tires had a problem. The wheel hub of the same vehicle was replaced by the same vehicle, and the road test was almost unchanged, the steering wheel was still jitter. Wheel hub tires and suspension arm ball heads, which affect the steering wheel jitter, are all normal. Why does the steering wheel shake? Lift up the vehicle and check the chassis suspension again. If the vehicle is 44K, will there be any problem with the axle? Check the two front axle, the appearance of the dust cover is not damaged, no oil leakage. The sloshing half axis ball cage, the space between the left and right sides of the cage is normal, the inner cages are left and right, and the left front is relatively open, but it is not like the open motion of the cage itself, checking the half axis connection, and finding that it is not a half axis loose, but a severe action with the half shaft connected by the right front differential through the middle connection axis through the engine oil shell. It was found through inspection that the fixed bearing of the intermediate shaft has worn out and the outer ring of the bearing has been worn out. The problem originally appeared here. Because the left front half axle of the S four drive car is short, it needs a middle shaft to pass through the oil pan and connect to the right front differential. The intermediate shaft is embedded with 1 bearings on the oil shell. Because the local environment temperature of the assembly is high, the lubricating oil in the bearing of the intermediate shaft is prolonged at high temperature for a long time. Work, grease drying, forming blocks, can not be lubricated, leading to bearing wear, loose and serious, vehicle driving up the left front half shaft without intermediate support, causing vehicles to drive a lot of movement, leading to abnormal steering wheel jitter. Troubleshooting: change the left front half shaft to connect the intermediate shaft, and the trial run is normal. Everything is normal at high speed / low speed. Failure summary: check carefully, because the installation location is hidden, usually do not check in place, remind S class IV drive vehicles should focus on inspection.