Overview
The ZF 4644.306.604 PISTON is a critical hydraulic actuation component engineered specifically for the WG 180, WG 200, and WG 250 series transmissions. This OEM genuine part functions as a precision-machined pressure vessel within the clutch pack assembly, converting hydraulic fluid force into linear mechanical motion to engage or disengage gear sets. The SKU 4644.306.604 sits directly within the transmission housing, interfacing with the valve body and clutch drums to ensure smooth power transfer under heavy-duty industrial loads. As a genuine ZF component, it guarantees exact dimensional tolerances and material integrity required for sustained high-torque applications.
Symptoms of Failure
- Erratic gear engagement or delayed shifting: When the 4644.306.604 piston wears, hydraulic pressure bleeds past the sealing surfaces, causing hesitation or harsh engagement when shifting between forward and reverse gears.
- Internal transmission oil leaks: A cracked or scored piston face allows transmission fluid to bypass the clutch pack, resulting in visible oil seepage around the bell housing or cooler lines.
- Clutch pack slippage under load: Worn piston seals reduce clamping force on the clutch discs, leading to RPM flare during acceleration or when climbing grades in WG 200 series equipment.
- Metallic debris in transmission fluid: Advanced piston wear generates aluminum or steel particles that contaminate the hydraulic circuit, often detected during routine oil analysis.
Technical Specifications
| Specification | Value |
|---|---|
| Part Number | 4644.306.604 |
| Material | High-strength aluminum alloy with hardened steel wear ring |
| Outer Diameter | 120 mm (estimated) |
| Inner Diameter | 85 mm (estimated) |
| Height | 45 mm (estimated) |
| Weight | 0.85 kg (1.87 lbs) |
| OEM Reference | ZF 4644.306.604 |
| Seal Type | Integrated PTFE lip seal |
Compatibility
This piston is designed for the ZF WG 180, WG 200, and WG 201 series transmissions, as well as the WG 250 series. It is a direct replacement for units manufactured between 2005 and 2023. The 4644.306.604 piston is installed inside the TRANSMISSION HOUSING (4644101175) and mates with the TRANSMISSION HOUSING (4644301221) to form the clutch cylinder assembly. For proper identification, always verify the TYPE PLATE (0730365067) on your transmission, and secure the assembly using the GROOVED STUD (0631311009) during installation.
Related Components
| Part Number | Name | Function |
|---|---|---|
| 4644101175 | TRANSMISSION HOUSING | Main structural casing for gear and clutch assembly |
| 4644301221 | TRANSMISSION HOUSING | Secondary housing section for clutch cylinder |
| 0730365067 | TYPE PLATE | Identification plate with transmission serial number |
| 0631311009 | GROOVED STUD | Fastening stud for piston retention |
| 4644303060 | COVER PLATE | Seals the piston chamber |
| 4644303061 | COVER PLATE | Alternate cover plate variant |
| 0634306525 | O-RING | Hydraulic seal between piston and housing |
| 0636305026 | SCREW PLUG | Oil drain or pressure port plug |
| 0501316470 | BREATHER | Pressure equalization vent |
| 4644301279 | SCREEN SHEET | Filter mesh for hydraulic fluid |
