Overview
The ZF 4644.137.004 EMERGENCY STEERING PUMP is a critical hydraulic component engineered specifically for the WG180 and WG200 transmission series. This OEM genuine part ensures that steering functionality remains available even during primary pump failure, providing a redundant hydraulic circuit for safety-critical maneuvers. Positioned within the transmission’s auxiliary hydraulic system, the pump engages automatically when main steering pressure drops, safeguarding vehicle control in demanding industrial applications. The SKU 4644.137.004 is precision-machined to ZF’s exacting tolerances, guaranteeing seamless integration with the 4644105475: DISCONNECTION coupling and the 4642303097: OUTPUT FLANGE assembly.
Symptoms of Failure
- Intermittent steering loss during low-engine RPM: When the emergency pump wears, hydraulic pressure drops below threshold, causing unresponsive steering at idle speeds.
- Audible whining or grinding from the transmission housing: Worn internal gears or bearings produce a high-pitched noise, often mistaken for transmission fluid issues.
- External oil seepage around the pump mounting flange: Degraded seals allow hydraulic fluid to escape, leaving visible drips on the 4644101134: TRANSMISSION HOUSING.
- Delayed engagement of emergency steering mode: A failing pump takes longer to activate, creating a dangerous lag in steering response during sudden pressure drops.
Technical Specifications
| Parameter | Value |
|---|---|
| Part Number (SKU) | 4644.137.004 |
| OEM Reference | ZF 4644.137.004 |
| Material | High-strength aluminum alloy with hardened steel gears |
| Weight | 4.2 kg (9.3 lbs) |
| Dimensions (L x W x H) | 210 mm x 120 mm x 95 mm |
| Max Operating Pressure | 180 bar |
| Flow Rate | 22 L/min at 1500 RPM |
| Mounting Bolt Torque | 45 Nm (use 0636020211: HEXAGON SCREW) |
Compatibility
This emergency steering pump is designed for the ZF WG180 and ZF WG200 series transmissions, commonly found in heavy-duty forklifts, wheel loaders, and industrial tractors. It directly replaces OEM part 4644.137.004 and is compatible with all sub-variants of these series, including WG180/200 models with auxiliary hydraulic take-offs. For proper sealing, pair this pump with the 0634303485: O-RING and the 4644301247: THREADED BUSH during installation.
Related Components
| Part Number | Name | Function |
|---|---|---|
| 4644105475 | DISCONNECTION | Couples emergency pump to transmission drive |
| 4642303097 | OUTPUT FLANGE | Transfers hydraulic torque to steering gear |
| 0636020211 | HEXAGON SCREW | Secures pump mounting bracket |
| 4644101134 | TRANSMISSION HOUSING | Encloses pump and hydraulic passages |
| 4644301349 | HOUSING | Protects internal pump components |
| 0730365125 | TYPE PLATE | Identifies pump specifications |
| 0631311009 | GROOVED STUD | Aligns pump during assembly |
| 0636305019 | SCREW PLUG | Seals hydraulic test ports |
| 4644301247 | THREADED BUSH | Provides wear-resistant mounting point |
| 0634303485 | O-RING | Prevents fluid leaks at pump interface |
