A quarry operation reported that a Volvo L220H wheel loader was losing power on steep inclines, with the transmission temperature gauge spiking into the red zone after just an hour of work. The operator noted that the machine felt like it was "slipping" in high gear, particularly when carrying a full bucket.
The L220H utilizes a power-shift transmission with a torque converter lock-up clutch that engages in higher gears to improve fuel efficiency and reduce heat. A diagnostic scan revealed an "active fault" for transmission slippage. The technician first checked the transmission oil level and condition. The oil was dark brown and had a strong burnt smell, indicating severe thermal breakdown.
The technician focused on the torque converter lock-up solenoid valve located on the transmission control valve body. The lock-up clutch is designed to mechanically couple the engine to the transmission input shaft, bypassing the fluid coupling. If the lock-up valve fails to open, the transmission relies entirely on fluid coupling, generating massive heat due to turbulence and shear.
The valve body was removed and disassembled. The lock-up solenoid spool was found stuck in the closed position by a sludge of varnish and friction material debris. This varnish was caused by the transmission oil overheating in the past. Additionally, the transmission suction filter screen was 60% plugged with the same debris, restricting oil flow to the pump. This low flow prevented the lock-up clutch from applying enough pressure to engage, causing it to slip and generate even more heat.
The repair involved flushing the entire transmission system with a specialized solvent, replacing the burnt oil, and installing a new lock-up solenoid valve and filter cartridge. The torque converter was cut open and inspected; the lock-up friction plates were found to be glazed but reusable after a light scuffing. After reassembly, the loader was tested on a steep ramp. The lock-up engaged firmly at 12 mph, the temperature stabilized at a normal 95°C, and the power loss was completely eliminated.
