An aggregate plant reported that a John Deere 744K wheel loader would lose all power when climbing a ramp into a hopper. The engine would race, but the machine would barely move. The transmission temperature gauge was pegged at the maximum limit. The operator stated the machine had been working fine until the end of the previous shift.
The technician first checked the transmission oil level and condition. The oil was black and smelled severely burnt, indicating massive clutch slippage or converter failure. A pressure gauge was installed at the main transmission pump. The pressure was within spec at idle but dropped to near zero when the machine was put under load.
The technician dropped the transmission sump pan. The suction screen was completely coated in a thick layer of friction material from the clutch packs. However, the source of the heat was suspected to be the torque converter. The transmission was removed, and the torque converter was cut open. The stator (the stationary element inside the converter that redirects fluid flow) had broken free from its one-way clutch.
The stator is responsible for multiplying torque. When it breaks loose, the converter becomes a simple fluid coupling with no torque multiplication. This caused the engine power to be converted into heat rather than motion, burning the clutches as they struggled to engage. The clogged suction screen exacerbated the issue by starving the pump of oil.
The repair involved installing a new remanufactured torque converter, a new main pump, and a clutch pack rebuild kit. The transmission oil cooler was also replaced, as the burnt oil had left a varnish layer inside the tubes. After reassembly and a thorough flush, the loader climbed the ramp with full power, and the transmission temperature stabilized at a normal 85°C.
