What are the causes of driveshaft dynamic imbalance?
2 Answers
Driveshaft dynamic imbalance is caused by: axial movement of the universal joint cross shaft in the small driveshaft assembly, clearance in the driveshaft sliding spline, centering accuracy at both ends of the driveshaft assembly connection, elastic deformation of the driveshaft during high-speed operation, and process treatment when spot welding balance plates on the driveshaft. The driveshaft is a high-speed rotating body with minimal support, making its dynamic balance crucial. Before leaving the factory, driveshafts undergo dynamic balance testing and adjustments on balancing machines. For front-engine rear-wheel-drive vehicles, the driveshaft transmits rotation from the transmission to the final drive axle, which can consist of multiple sections connected by universal joints.
I've encountered many cases of unbalanced drive shafts during car repairs. The main reasons are often incomplete symmetry during manufacturing, leading to uneven weight distribution, which causes severe shaking when the car is running. Some cars have slightly twisted shaft necks or flanges from the factory, and when rotating at high speeds, the centrifugal force amplifies, causing the entire car to vibrate. There are also wear issues, such as the drive shaft being bent by road stones or internal parts rusting and deforming, making it unstable during operation. Improper installation is another culprit—loose screws or unsecured couplings can easily cause shaking. It's also common for balance weights to fall off and not be replaced. Those small lead weights are meant to offset weight deviations, and if not properly maintained, you can feel the steering wheel trembling at high speeds. These issues can range from being noisy to damaging other components, so if you notice abnormal shaking while driving, don't delay—promptly visit a professional shop to check the drive shaft and related parts.
