A sand and gravel site reported that a SEM 652 wheel loader (a Shandong Engineering Machinery brand) had a delay of 3-4 seconds when shifting into Forward gear. Once moving, the machine felt "sluggish" and lacked digging power, requiring the operator to rev the engine high to move the load.
The technician checked the transmission oil level, which was normal. He connected a pressure gauge to the "Forward Clutch" test port. In neutral, the pressure was 0. When shifted into Forward, the pressure rose slowly to 1.0 MPa (spec is 1.5 MPa). The slow rise explained the shift delay, and the low pressure explained the clutch slipping.
He removed the transmission valve body to check the "Modulating Valve." The valve spool was free. However, he found the "Forward Clutch Piston" seals (O-rings) were hard and cracked. The piston is located inside the torque converter housing. The cracked seals allowed hydraulic pressure to leak past the piston, preventing the clutch pack from engaging fully.
Furthermore, upon disassembling the torque converter, he found the "Stator Support Bushing" was worn. The stator support is the stationary shaft that the torque converter rotates around. The wear allowed the converter to wobble, misaligning the pump drive gear. This wear debris had contaminated the valve body.
The repair involved replacing the forward clutch piston seals and the stator support bushing. The transmission filter was replaced. Because the wear debris had circulated, the technician flushed the system with fresh oil three times. After reassembly, the pressure built up instantly to 1.5 MPa, and the loader engaged gears sharply.
