A mining site reported that a Volvo L220H wheel loader would lose power when traveling up a steep ramp in 4th gear (high range). The engine RPM would stay high, but the machine speed would drop drastically. In 1st and 2nd gears (low range), the machine pulled strongly. The transmission temperature was within normal limits.
The technician connected the Volvo Tech Tool (diagnostic software) and monitored the "Lock-Up Solenoid" status. The torque converter in the L220H has a "lock-up" clutch that mechanically connects the engine to the transmission for high-speed efficiency. The data showed that the solenoid was receiving the "ON" signal, but the actual slip speed (difference between engine RPM and transmission input RPM) was high.
He measured the electrical resistance of the solenoid, which was within spec. He then checked the hydraulic pressure at the lock-up clutch port. The pressure was fluctuating between 5 bar and 15 bar, indicating the clutch was chattering. The technician removed the hydraulic oil pan and found the transmission suction filter was partially clogged with fine black dust (clutch material).
This debris was restricting flow to the lock-up control valve. The erratic pressure prevented the lock-up clutch from fully engaging, causing it to slip and overheat. The technician flushed the transmission system, replaced the filter, and installed a new lock-up solenoid valve (the old one had a weak magnetic coil due to overheating). After refilling with fresh oil (Volvo Transmission Oil 115), the lock-up clutch engaged firmly, and the loader maintained speed on the ramp.
