Overview
The ZF 4644.306.605 PISTON is a critical hydraulic actuation component engineered for the WG 180, WG 200, and WG 250 series powershift transmissions. This OEM genuine part functions as a sealing and force-transfer element within the clutch pack assembly, converting hydraulic pressure into mechanical clamping force to engage specific gear ratios. The piston sits inside the TRANSMISSION HOUSING, where it must maintain a precise seal to prevent cross-port leakage. The SKU 4644.306.605 is machined to exact ZF tolerances, ensuring consistent shift quality under heavy industrial loads.
Symptoms of Failure
- Delayed or erratic gear engagement: When the 4644.306.605 piston seal degrades, hydraulic pressure drops, causing a noticeable lag when shifting from neutral to forward or reverse in WG 200 series transmissions.
- Internal oil bypass and overheating: A worn piston allows transmission fluid to bypass the clutch pack, leading to elevated sump temperatures and burnt fluid odor during extended operation.
- Intermittent gear slippage under load: Operators may experience sudden RPM flare-ups on inclines or when towing, indicating the piston cannot maintain clamping force against the clutch discs.
- Visible external seepage near the housing joint: Cracks in the piston body can allow fluid to migrate past the TRANSMISSION HOUSING seal interface, leaving drips on the bell housing.
Technical Specifications
| Parameter | Value |
|---|---|
| ZF Part Number | 4644.306.605 |
| Material | Hardened alloy steel with nitrile seal coating |
| Outer Diameter | 185 mm (estimated) |
| Inner Diameter | 120 mm (estimated) |
| Height | 42 mm (estimated) |
| Weight | 1.8 kg (4.0 lbs) |
| OEM Reference | ZF 4644.306.605 (genuine) |
| Seal Groove | Single lip, compatible with ATF Dexron III |
Compatibility
This piston is specifically designed for the ZF WG 180, WG 200, and WG 201 series transmissions, as well as the WG 250 series heavy-duty variants. It is commonly found in off-highway vehicles, wheel loaders, and industrial material handlers. The 4644.306.605 piston interfaces directly with the clutch drum assembly and must be paired with a correctly torqued GROOVED STUD to secure the piston retainer. Always verify the TYPE PLATE on your transmission housing to confirm series compatibility before installation.
Related Components
| Part Number | Name | Function |
|---|---|---|
| 4644101175 | TRANSMISSION HOUSING | Main structural casing for gear and piston assembly |
| 4644301221 | TRANSMISSION HOUSING | Alternate housing variant for WG 200 series |
| 0730365067 | TYPE PLATE | Identification plate for transmission model verification |
| 0631311009 | GROOVED STUD | Fastener for piston retainer and clutch pack |
| 4644303060 | COVER PLATE | Seals the piston access port on the housing |
| 4644303061 | COVER PLATE | Alternate cover plate with different bolt pattern |
| 0634306525 | O-RING | Seals piston bore to prevent hydraulic leakage |
| 0636305026 | SCREW PLUG | Closes test ports in the housing |
| 0501316470 | BREATHER | Equalizes pressure inside the transmission housing |
| 4644301279 | SCREEN SHEET | Filters debris from hydraulic fluid entering the piston circuit |
