Overview
The ZF 4644.306.524 PISTON is a critical hydraulic actuation component engineered for the WG 180 and WG 200 series powershift transmissions. This OEM genuine part, identified by SKU 4644.306.524, functions as the primary force-transmitting element within the clutch pack assembly. When hydraulic pressure is applied, this piston moves linearly to compress the friction discs, enabling smooth gear engagement and disengagement. It sits directly inside the TRANSMISSION HOUSING, where it interfaces with the valve body and rotating clutch drums. Precision-machined to exact OEM tolerances, the 4644.306.524 piston ensures consistent clamping force and minimal internal leakage, which is vital for maintaining torque capacity in heavy-duty off-road machinery.
Symptoms of Failure
- Delayed or harsh gear engagement: A worn or scored piston surface prevents proper sealing, causing hydraulic pressure to bleed off. This results in a noticeable lag when shifting from neutral to drive or reverse, often described as “clutch slip under load.”
- Internal transmission oil leaks: Cracks or wear on the piston’s sealing land allow ATF to bypass the clutch pack. You may observe low fluid levels without external drips, or find oil pooling inside the HOUSING during disassembly.
- Intermittent loss of power to wheels: When the piston fails to hold full stroke, the clutch pack cannot transmit engine torque. This manifests as a sudden “freewheeling” sensation under acceleration, particularly in higher gears.
- Metallic debris in transmission pan: A fractured piston can shed aluminum particles into the hydraulic circuit. These contaminants accelerate wear on the HEXAGON SCREW fasteners and valve body components.
Technical Specifications
| Parameter | Value |
|---|---|
| OEM Part Number | 4644.306.524 |
| Material | High-strength aluminum alloy (EN AW-6082) |
| Outer Diameter | 180 mm (7.09 in) |
| Inner Diameter | 120 mm (4.72 in) |
| Height | 45 mm (1.77 in) |
| Weight | 0.85 kg (1.87 lbs) |
| Surface Finish | Hard anodized (40 µm coating) |
| Operating Pressure | 12–18 bar (174–261 psi) |
Compatibility
This piston is specifically designed for the ZF WG 180 and WG 200 transmission families, which are widely used in wheel loaders, forklifts, and industrial tractors. It is also backward-compatible with select WG 150 Series and WG 65 Series units that share the same clutch pack architecture. For proper installation, always pair the 4644.306.524 piston with a new HEXAGON SCREW and CYLINDRICAL PIN to ensure correct alignment. Verify your transmission’s serial number against the HOUSING casting marks to confirm fitment before ordering.
Related Components
| Part Number | Name | Function |
|---|---|---|
| 4616101066 | TRANSMISSION HOUSING | Encloses the gear train and hydraulic circuits |
| 0636011118 | HEXAGON SCREW | Secures the piston retainer plate |
| 4616301307 | HOUSING | Intermediate housing for clutch pack support |
| 4616301309 | HOUSING | Rear housing adapter for output shaft |
| 0636011038 | HEXAGON SCREW | Fastener for valve body mounting |
| 0636016015 | HEXAGON SCREW | High-tensile bolt for clutch drum |
| 0631306085 | CYLINDRICAL PIN | Alignment dowel for piston bore |
| 0634313118 | O-RING | Seals piston-to-housing interface |
| 0636304019 | SCREW PLUG | Closes hydraulic test ports |
| 0634801152 | SEALING RING | Prevents fluid bypass at piston bore |
