Overview
The ZF 4644.306.265 PISTON is a critical hydraulic actuation component engineered for the WG 180 and WG 200 series transmissions. This OEM genuine part functions within the clutch pack assembly, converting hydraulic pressure into mechanical force to engage and disengage specific gear sets. As a precision-machined component, the piston ensures consistent clamping force on the friction discs, directly influencing shift quality and torque transfer. The SKU 4644.306.265 is manufactured to ZF’s exacting tolerances, making it a direct replacement for worn units in heavy-duty industrial applications. This piston works in concert with the 4642101109: TRANSMISSION HOUSING and the 4642301205: TRANSMISSION HOUSING to maintain proper alignment and sealing within the valve body area.
Symptoms of Failure
- Delayed or harsh gear engagement: A worn piston seal or scored piston surface causes insufficient hydraulic pressure, leading to noticeable lag or jarring shifts when moving from neutral to drive or reverse.
- Internal transmission oil leaks: Degraded piston rings allow pressurized ATF to bypass the piston, resulting in low line pressure and visible fluid puddling under the bell housing area.
- Slipping in higher gears: As the piston fails to maintain clamping force, the clutch pack slips under load, causing RPM flare without corresponding vehicle acceleration, particularly in 3rd and 4th gears.
- Erratic shift timing: A failing piston creates inconsistent hydraulic feedback, causing the transmission to shift too early or too late, often accompanied by a whining noise from the pump struggling to compensate.
Technical Specifications
| Part Number | 4644.306.265 |
| Material | Hardened alloy steel with PTFE seal coating |
| Outer Diameter | 98.5 mm |
| Inner Diameter | 42.0 mm |
| Height | 34.2 mm |
| Weight | 0.42 kg |
| OEM Reference | ZF 4644.306.265 (Genuine) |
| Surface Finish | Ground and polished, Ra 0.4 µm |
Compatibility
This piston is specifically designed for ZF’s WG series powershift transmissions. Verified compatibility includes the WG 180 Series and WG 200 Series, where it serves as the primary actuation piston for the forward clutch pack. It also functions in the WG 100 Series, WG 150 Series, and WG 201 Series with identical hydraulic circuit configurations. Always verify the piston bore condition in the 0730365125: TYPE PLATE to confirm correct series identification. The piston assembly requires the 0631311009: GROOVED STUD for proper retention during installation.
Related Components
| Part Number | Name | Function |
|---|---|---|
| 4642101109 | TRANSMISSION HOUSING | Encloses the gear train and valve body assembly |
| 4642301205 | TRANSMISSION HOUSING | Rear housing section supporting output shaft |
| 0730365125 | TYPE PLATE | Identification plate for transmission series verification |
| 0631311009 | GROOVED STUD | Fastener for piston retention in clutch pack |
| 4642301168 | SCREEN SHEET | Filter screen for hydraulic fluid debris |
| 4642301169 | SCREEN SHEET | Secondary filter screen for valve body protection |
| 0636100621 | HEXAGON SCREW | Mounting screw for housing attachment |
| 4642301186 | SCREEN SHEET | Fine mesh screen for oil pump intake |
| 4644106231 | SHIFT SYSTEM | Hydraulic control unit for gear selection |
| 4644306470 | GASKET | Sealing gasket for piston housing interface |
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