Transmission First Shaft Rear Bearing Damage Problem

A CA6440 light passenger car, after traveling approximately 40,000 kilometers, experienced repeated damage to the rear bearing (50306#) of the first shaft in the transmission. During the troubleshooting process, the transmission was disassembled several times, but no visible abnormalities were found. The torsion bar spring adjustment screw was measured at a height of 42mm, which met the specifications. The orientation of the spline groove between the torsion bar spring and the two fixed arms was checked, and the levers were fully collapsed without any issues detected. Only the rubber pad between the left torsion bar spring adjustment screw and the rear fixed arm was damaged. After replacing the rubber pad, the issue was resolved. To date, the vehicle has traveled over 5,000 kilometers, and the bearing is operating normally.

The front suspension of the CA6440 uses a vertical torsion bar spring independent suspension system. The connecting rod is attached to both the frame and the steering knuckle. The torsion bar spring connects to the lower control arm through a twisting arm, while the lower control arm links to the front beam and the frame, forming the front support structure. The torsion bar spring is connected to the transmission support beam via the fixed arm and the adjustment screw, and the transmission support beam is then connected to the frame to form the rear support. The system transmits forces and moments in all directions, with the torsion bar spring absorbing torque. When the front wheel encounters horizontal impact forces, the force is transmitted through the torsion bar spring to the transmission support beam and the frame. When the impact is in the straight direction, the torsion bar spring converts it into a changing torque, which is then transmitted to the transmission support beam and the frame. Various impact forces and moments from the front wheel are gradually absorbed by the tire, damper, knuckle, yoke spring, transmission beam, and frame, ensuring the vehicle's smoothness and safety.

To ensure the front wheels can effectively absorb forces and moments in all directions, a certain pre-torque force is applied to the torsion bar spring. This pre-torque acts like a large spring, working with the damper to reduce vibration and absorb energy generated by the front wheel’s forces and moments. To maintain balance, both torsion bars must have equal pre-torque forces, requiring strict adherence to technical specifications during installation and adjustment. This ensures proper force and torque transmission and balanced energy absorption during operation.

When the rubber pad on the torsion bar spring was damaged, the adjustment screw was re-tightened. Even though the car was stationary, the height of the adjustment screw remained the same. However, this effectively increased the length of the adjustment screw on the left lever, reducing the pre-torque of the left torsion bar spring. As the vehicle moved, the imbalance caused by the unequal pre-torque led to uneven force distribution. The transmission, directly connected to the beam that transmits and absorbs forces from the front wheels, also experiences stress. This imbalance can lead to excessive pressure on the first shaft of the transmission, particularly on its front and rear bearings. While the front bearing is a sliding bearing that resists damage better than a rolling bearing, the rear bearing is more vulnerable. Over time, this imbalance results in damage to the rear bearing of the first shaft in the transmission.

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