A limestone quarry reported that a Longking ZL50CN wheel loader would slip out of gear when climbing hills, and reverse speed was significantly lower than forward speed. The torque converter oil temperature was consistently high.
The technician diagnosed the transmission system. First, he checked the pressure of the 1st and 2nd gear clutches. The pressure was steady at 1.2 MPa in neutral but dropped to 0.8 MPa when put into reverse under load. This pointed to a leak in the reverse clutch circuit or the torque converter.
He removed the transmission and torque converter assembly. Upon inspection, he found the "Stator Shaft Spline" (the internal splines that hold the stator support) was severely worn. The stator is the stationary element in the torque converter that multiplies torque. If the spline wears out, the stator rotates with the turbine, eliminating the torque multiplication effect. This caused the machine to feel "sluggish" and slip.
Furthermore, the "Transmission Control Valve Body" (distribution valve) was cracked. The crack was located between the reverse pressure channel and the oil return channel. This internal leakage robbed the reverse clutch of pressure. The crack was caused by hydraulic hammering (pressure spikes) due to a failed accumulator bladder.
The repair involved replacing the torque converter assembly (stator and turbine) and welding the valve body (aluminum welding) or replacing it with a new cast iron valve body for better durability. He also replaced the damaged "Accumulator Bladder" and seals. After reassembly, the loader's reverse speed matched forward speed, and the slipping issue was resolved.
