Overview
The ZF 4644.306.378 PISTON is a critical hydraulic actuation component engineered for the WG 180 and WG 200 series transmissions. This OEM genuine part converts hydraulic pressure into mechanical force to engage clutch packs and modulate gear shifts. Positioned within the valve body and clutch drum assembly, the piston (SKU: 4644.306.378) ensures precise oil flow control for smooth power delivery under heavy loads. When paired with a properly functioning 5838109007: DIFFERENTIAL, this piston maintains consistent pressure regulation across the transmission’s hydraulic circuit.
Symptoms of Failure
- Delayed or harsh shifting – Worn piston seals cause pressure loss, leading to sluggish engagement or abrupt gear changes during acceleration.
- Transmission fluid leaks – Cracks or scoring on the piston body allow ATF to bypass seals, resulting in visible drips near the bell housing or pan.
- Slipping in higher gears – Inadequate clamping force from a degraded piston causes clutch pack slippage, particularly under torque in 4th or 5th gear.
- Erratic hydraulic noise – A failing piston can produce a whining or buzzing sound from the valve body as hydraulic pressure fluctuates.
Technical Specifications
| Parameter | Value |
|---|---|
| Part Number | 4644.306.378 |
| Material | Hard-anodized aluminum alloy |
| Outer Diameter | 68.5 mm |
| Inner Diameter | 42.0 mm |
| Height | 24.3 mm |
| Weight | 0.14 kg |
| OEM Reference | ZF 4644.306.378 |
| Seal Type | PTFE lip seal (integrated) |
Compatibility
This piston is specifically designed for ZF WG 180 and WG 200 series transmissions, commonly found in medium-duty trucks, buses, and off-highway equipment. It directly replaces OEM units in models such as WG180-5, WG200-6, and WG200-8. For complete clutch pack restoration, this piston works in conjunction with the 0750117075: TAPER ROLLER BEARING and the 2095209019: DIFFERENTIAL assembly. Always verify the 0631329086: SPRING PIN alignment during installation to prevent hydraulic cross-leakage.
Related Components
| Part Number | Name | Function |
|---|---|---|
| 5838109007 | DIFFERENTIAL | Distributes torque between output shafts |
| 0750117075 | TAPER ROLLER BEARING | Supports axial and radial loads on planetary gears |
| 2095209019 | DIFFERENTIAL | Balances wheel speed during turns |
| 0631329086 | SPRING PIN | Secures piston return spring alignment |
| 5838300817 | THRUST WASHER | Reduces axial friction in clutch drum |
| 5838300682 | DIFFERENTIAL AXLE | Transfers power to differential gears |
| 5838300811 | THRUST WASHER | Controls end-play in planetary carrier |
| 5841302064 | THRUST WASHER | Prevents wear between clutch plates |
| 5838300137 | OUTER CLUTCH DISK | Provides friction surface for gear engagement |
| 5838300138 | INNER CLUTCH DISK | Transfers torque through clutch pack |
