Common fault diagnosis and troubleshooting of torque-shift transmission system
May 15,2025
Abnormal pressure in torque-shift transmission hydraulic system
(1) Fault phenomenon
The pressure of the torque-shift transmission hydraulic system can be reflected on the pressure gauge. Under normal circumstances, it should be 1.4~1.6MPa.
The minimum normal pressure should not be less than 1.1MPa. If the system pressure is too high, too low or zero during operation, it is abnormal. (2) Fault cause and troubleshooting
1. Too high pressure
a. The main pressure valve pressure is adjusted too high or stuck. The pressure of the loader has not been adjusted during use, and the pressure suddenly increases because the main pressure valve core is stuck. Generally, the valve core is stuck in the low pressure position, but if there is foreign matter in the valve core, it can also make the valve difficult to open, so that the pressure rises to beyond the normal working range.
Remove the valve, disassemble and clean it, and grind it with a little aluminum oxide grinding paste until it is not stuck, then clean it and reinstall it, and readjust the main pressure, inlet pressure, and outlet pressure (if conditions permit, it should be done on the test bench).
b. The pressure gauge indicates too high. When the diesel engine is not started, the pressure gauge indication should be zero. If it is not zero, but indicates a certain value in advance, the pressure when the system is working will be the actual pressure plus the pre-indicated pressure. In this case, a qualified pressure gauge should be replaced.
Pressure is too low
a. The oil level in the transmission case is too low. There are two oil level high and low inspection switches on the side of the case. The oil level is normal between the high and low inspection switches. If the oil level is too high, the excess oil should be released; if the oil level is too low, the cause should be found out first, and then the corresponding measures should be taken.
If the oil level in the transmission case is low, the oil pump will suck in air, bubbles will be generated in the oil tank, there will be noise, the pressure gauge indication will be unstable, and the swing will be violent. If the oil level is too low, the oil pump will not oil, and the oil pressure gauge will have no pressure indication. If the oil level is added to the standard position after repairing or replacing the assembly, the loader is started, and the pressure is normal at the beginning, but the pressure drops rapidly after a few seconds and drops below the low switch position. In this case, just add enough oil.
Working oil leaks out. This phenomenon is easy to observe. Solve the oil leakage problem first. Loss during maintenance, such as replacing a new oil pump, radiator, oil pipe, etc., and not adding the lost oil after replacement, the oil should be added to the standard height.
b. The filter screen in the transmission oil pan is too dirty and blocked, and the oil flow is not smooth. The main sources of dirt are: abnormal wear and peeling in the system, grinding debris generated by long-term work, or peeling on the surface of parts; the loader's operating environment is harsh, and the transmission is not maintained after ventilation, causing dust to enter the transmission and form sludge; the transmission is not cleaned during repair. When cotton yarn is used to scrub the parts and the inner surface of the transmission housing, the cotton yarn hair hangs on the parts and concentrates on the filter screen with the flow of working oil.
The filter screen in the transmission housing is not smooth, and the oil flow capacity is limited. When the oil pump sucks oil, the low-pressure part must produce a certain vacuum. The higher the speed of the oil pump, the greater the vacuum produced. After the filter is clogged, the pressure on the meter is basically normal when the diesel engine is idling. The greater the throttle, the lower the pressure, accompanied by obvious noise, and the propulsion force of the loader wheels also decreases.
For the filter blockage caused by the above reasons, on the one hand, the filter should be cleaned regularly in combination with seasonal maintenance, and on the other hand, attention should be paid to the maintenance of the ventilation port of the transmission to prevent dust from easily entering the transmission. Especially when repairing the transmission, do not use cotton yarn to clean, but use a clean brush and washing oil to clean the parts. Use compressed air to clean the oil channels and corners that are not easy to observe, and use soft dough to stick the rough and uneven places.
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