Overview
The ZF 4644.306.322 PISTON is a critical hydraulic actuation component engineered for the WG 180, WG 200, and WG 201 series transmissions. This OEM genuine part functions as the primary force-translating element within the clutch pack assembly, converting hydraulic pressure into mechanical clamping force to engage specific gear ratios. The SKU 4644.306.322 sits directly inside the transmission housing, where it interfaces with the valve body and rotating clutch drums. When this piston fails, the entire shift sequence becomes compromised, leading to pressure loss and erratic transmission behavior.
Symptoms of Failure
- Delayed or harsh shifting – A worn 4644.306.322 piston allows hydraulic fluid to bypass the seal, causing soft engagement or sudden jarring shifts when the transmission finally catches.
- Internal transmission oil leaks – Cracks or scoring on the piston surface permit ATF to escape into the sump, resulting in low line pressure and visible puddling under the bell housing.
- Gear slipping under load – As the piston loses its ability to hold pressure, the clutch pack fails to lock, causing the transmission to slip out of gear during acceleration or hill climbing.
- Erratic neutral-to-drive engagement – A sticking piston prevents clean engagement from park or neutral, often requiring multiple attempts or excessive throttle to move the vehicle.
Technical Specifications
| Parameter | Value |
|---|---|
| Part Number | 4644.306.322 |
| Material | High-strength aluminum alloy with hardened anodized coating |
| Outer Diameter | 85.0 mm (estimated) |
| Inner Diameter | 45.0 mm (estimated) |
| Height | 32.5 mm (estimated) |
| Weight | 0.42 kg (0.93 lbs) |
| OEM Reference | ZF 4644.306.322 (genuine) |
| Seal Grooves | 2 (for O-ring retention) |
Compatibility
This piston is specifically designed for the ZF WG 180, WG 200, and WG 201 series transmissions. It is a direct fit for all sub-variants within these families, including the WG 180-1, WG 200-2, and WG 201-3 models. The 4644.306.322 piston is not interchangeable with earlier WG 120 series units due to differences in bore diameter and seal configuration. Always verify your transmission model tag before ordering.
Related Components
| Part Number | Name | Function |
|---|---|---|
| 4644105475 | DISCONNECTION | Isolates hydraulic circuits during clutch pack engagement |
| 4642303097 | OUTPUT FLANGE | Transfers torque from the transmission to the driveshaft |
| 0636020211 | HEXAGON SCREW | Secures the piston assembly to the clutch drum |
| 4644101134 | TRANSMISSION HOUSING | Encloses and supports all internal rotating components |
| 4644301349 | HOUSING | Provides structural mounting for valve body and piston |
| 0730365125 | TYPE PLATE | Identifies transmission model and serial number |
| 0631311009 | GROOVED STUD | Aligns and positions the piston within the bore |
| 0636305019 | SCREW PLUG | Seals hydraulic passages in the piston cavity |
| 4644301247 | THREADED BUSH | Provides wear-resistant thread for piston retention |
| 0634303485 | O-RING | Prevents hydraulic fluid leakage around the piston |
