A wheel loader was brought in with a severe lack of power. It would drive across the lot fine, but when it pushed into a gravel bank, it stalled out instantly, as if the transmission was slipping. The engine RPM dropped, and the machine just sat there. The shop replaced the shift solenoids and the pump, but the stall remained.
We pulled the torque converter. Inside a torque converter are three elements: the impeller (driven by the engine), the turbine (driving the transmission), and the stator. The stator sits between them and redirects the fluid flow to multiply torque at low speeds. The stator rides on a one-way roller clutch. It locks up to redirect the oil when the engine is turning faster than the transmission (torque multiplication), and it freewheels when the speeds equalize (coupling phase).
The one-way clutch had shattered. When the operator pushed into the pile, the stator tried to lock up to multiply torque. But because the clutch was broken, the stator simply freewheeled backward. The converter lost all its torque multiplication. The engine power went straight into churning the oil, generating massive heat, but delivering zero pushing force to the transmission. Replacing the torque converter restored the stall speed and the pushing power. If a loader drives fine but won't push, the stator clutch is often the ghost.
