Troubleshooting for elevated oil level in loader transmission

A ZL-30C loader that has been in use for three years leaks oil from the vent hole of the torque converter gear chamber whenever the engine starts, and the oil level in the transmission oil pan gradually rises as it is used.

The transmission and torque converter of this machine are of a split structure. Its hydraulic system is composed of three independent circuits: the working device circuit, the control circuit and the steering circuit. The power of the engine drives the three gear pumps installed on the torque converter housing to work through the active gear on the pump wheel housing.

Analyzing the hydraulic system of this machine, there are mainly three reasons for oil leakage at the vent hole of the torque converter: First, the valve core of the outlet pressure valve is stuck, and the outlet pressure of the torque converter is greater than the inlet pressure. The second reason is that the oil seal at the guide wheel seat of the torque converter is damaged, causing the pressure oil inside the torque converter to leak from the guide wheel seat into the gear chamber of the torque converter, resulting in oil spraying from the vent hole. The third reason is that the oil seal at the shaft end of a certain hydraulic pump is damaged. When the engine starts, the viscosity of the hydraulic oil is high, and the pressure of the pump is relatively large. A large amount of hydraulic oil leaks from the oil seal at the shaft end of the pump, causing oil to seep through the vent hole of the torque converter. If the oil level in the transmission oil pan rises, it can only be that the hydraulic oil leaked into the torque converter gear chamber has leaked into the transmission oil pan through the connecting pipe between the torque converter and the transmission. In this case, it can only be that the oil seal at the shaft end of the steering hydraulic pump or the working gear hydraulic pump is damaged.

After disassembly and inspection, it was found that the oil seal at the shaft end of the steering hydraulic pump was damaged. After replacing the oil seal and conducting a test run, the fault phenomenon disappeared, and the analysis was verified.