Three seconds after the Shantui SD16 bulldozer was started, the operator found a large amount of oil spilled from the oil filler port of the transmission. The inspection found that the oil level of the rear axle tank dropped sharply while the oil spilled from the oil filler port of the transmission. The preliminary judgment is that the steering brake hydraulic system of the aircraft is malfunctioning. SD16 bulldozer steering brake hydraulic system is mainly composed of rear axle box, steering coarse filter, steering pump, steering fine filter, safety valve, steering clutch, brake cylinder, steering valve, and pipelines.

　　According to the working principle and maintenance experience of the steering hydraulic system of Shantui bulldozers, the maintenance master analyzed that the cause of this failure was the damage of the steering pump oil seal, which caused the hydraulic oil to leak from the steering pump to the inside of the transfer case, and the hydraulic oil inside the transfer case entered the transmission through the oil return pump. Internally, the oil inside the transmission increases and overflows from the oil filler port.

　　Further inspection and analysis of the reasons for the damage of the steering pump oil seal are as follows:

　　1:: Steering pump oil package is equipped with problems,

　　2: The steering brake system does not return oil smoothly.

　　First, check the steering pump. Replace the new steering pump, and adjust the hydraulic oil level of the transmission and rear axle box to the specified height and test the machine. After testing the machine for 5 minutes, we found that there was another hydraulic oil overflowing from the transmission refueling port, and the oil in the rear axle box was reduced, which indicated that the newly replaced steering pump oil seal was damaged.

　　Secondly, we analyzed the steering brake hydraulic system schematic diagram. Since the operator does not perform steering and braking operations, it is not necessary to consider whether there are problems with the steering valve and brake cylinder, and other hydraulic components of the steering brake hydraulic system should be checked.

　　Again, check other hydraulic components. The steering fine filter was intact after the disassembly inspection, the safety valve was not found to be stuck or blocked, and all the pipelines in the steering brake system were not found to be blocked. However, when the safety valve located on the upper panel of the rear axle box was disassembled and inspected, it was found that the oil return passage of the safety valve was not drilled through.

　　Finally, remove the safety valve, drill through the return oil passage of the safety valve located on the upper panel of the rear axle and install the safety valve, replace the steering pump oil seal and install it, and then test the locomotive. The cause of the fault is resolved.