Overview
The ZF 4644.026.238 6 WG 200(555/3) Powershift Transmission Assembly is a complete, factory-grade unit designed for heavy-duty off-highway machinery. This assembly integrates the torque converter, clutch packs, and planetary gear sets into a single, ready-to-install package. As the core of the WG 200 series, it manages power distribution from the engine to the driveline, enabling smooth, load-free shifting under full torque. The SKU 4644.026.238 specifically identifies the 6-speed configuration with a 555/3 ratio set, making it a direct replacement for worn or failed transmissions in wheel loaders, graders, and industrial tractors. This unit eliminates the need for piecemeal repairs, offering a drop-in solution that restores original performance and reliability.
Symptoms of Failure
When the ZF 4644.026.238 begins to fail, operators often notice distinct operational issues. Recognizing these signs early can prevent catastrophic driveline damage and costly downtime.
- Delayed or harsh engagement: A noticeable lag when shifting from neutral to forward or reverse, followed by a jarring clunk. This indicates worn clutch pack friction discs or degraded hydraulic pressure within the valve body.
- Transmission overheating and oil foaming: If the unit runs excessively hot, causing the hydraulic fluid to aerate and foam, it points to internal seal failure or a failing torque converter stator. This often accompanies a burnt smell from the oil.
- Gear slipping under load: The engine revs up without a corresponding increase in machine speed, particularly when climbing grades or pushing heavy loads. This is a classic sign of worn planetary gear sets or a failed one-way clutch.
- External oil seepage at the bell housing: Fluid leaking from the joint between the transmission and the engine indicates a failed input shaft seal or a cracked converter housing, leading to gradual fluid loss and eventual transmission starvation.
Technical Specifications
| Parameter | Specification |
|---|---|
| Part Number / SKU | 4644.026.238 |
| Series | WG 200 (6 WG 200) |
| Configuration | 6-Speed Powershift (555/3 Ratio) |
| Dry Weight (approx.) | 385 kg (849 lbs) |
| Overall Length | 720 mm (28.3 in) |
| Input Flange | SAE 3 (Standard) |
| Housing Material | High-Strength Cast Iron |
| OEM Reference | ZF 4644.026.238 / 6WG200 |
| Fluid Capacity | 18.5 Liters (4.9 Gallons) |
Compatibility
This complete assembly is engineered for the ZF WG 200 series of powershift transmissions. It is a direct fit for models utilizing the 6-speed, 555/3 gear ratio package. While the unit is specifically calibrated for the WG 200, it shares mounting patterns and hydraulic interfaces with the following ZF transmission families:
- ZF WG 200 (Primary application – all variants using the 555/3 ratio)
- ZF WG 180 (Limited compatibility – requires verification of bell housing and output flange dimensions)
- ZF WG 150 (Not compatible without significant adapter modifications)
- ZF 6WG 200 (Direct replacement for earlier 6-speed iterations)
Always cross-reference your existing transmission’s data plate with the SKU 4644.026.238 to ensure correct fitment. This unit is commonly used in Volvo L120/L150 wheel loaders and Case 921E graders, though it serves as a universal replacement for any machine originally equipped with a ZF WG200 6-speed powershift.
