Overview
The ZF 4661.375.012 PISTON is a critical hydraulic actuation component engineered for the WG 90 and WG 94 series transmissions. This OEM genuine part converts hydraulic pressure into mechanical force to engage clutch packs and shift gears within the transmission valve body. As a precision-machined component, the 4661.375.012 piston sits directly inside the 4661101001: TRANSMISSION HOUSING, where it must maintain a perfect seal to ensure consistent oil flow. Without this piston, the transmission cannot modulate line pressure for smooth gear engagement.
Symptoms of Failure
- Delayed or harsh shifting: A worn 4661.375.012 piston causes erratic clutch engagement, leading to noticeable gear slip or jarring shifts during acceleration.
- Internal hydraulic leaks: Cracks or scoring on the piston surface allow transmission fluid to bypass, resulting in low line pressure and overheating.
- Inability to hold gear: When the piston fails to seal against the 4661301007: HOUSING, the transmission may unexpectedly drop out of gear under load.
- Contaminated fluid: Metal debris from a deteriorating piston circulates through the system, accelerating wear on the 0631306174: CYLINDRICAL PIN and valve body.
Technical Specifications
| Parameter | Specification |
|---|---|
| Part Number (SKU) | 4661.375.012 |
| Material | Hardened alloy steel with nitrided surface |
| Outer Diameter | 42.5 mm |
| Inner Diameter | 18.2 mm |
| Height | 34.8 mm |
| Weight | 0.185 kg |
| OEM Reference | ZF 4661.375.012 |
| Seal Compatibility | Requires 0634100633: O-RING |
Compatibility
This piston is designed for ZF WG series transmissions with hydraulic shift control. It is directly compatible with the WG 90 and WG 94 series, and also fits the WG 180, WG 200, and WG 210 models when used with the correct 4661301093: TUBE assembly. The 4661.375.012 piston is not interchangeable with electronic shift models (e.g., Ecolife) without modifying the valve body. Always verify the piston bore condition in the transmission housing before installation.
Related Components
| Part Number | Name | Function |
|---|---|---|
| 4661101001 | TRANSMISSION HOUSING | Main structural casing that houses the piston and clutch pack |
| 4661301007 | HOUSING | Secondary housing that guides piston movement |
| 4661301093 | TUBE | Hydraulic fluid conduit connecting piston to valve body |
| 0631306174 | CYLINDRICAL PIN | Alignment pin for piston bore positioning |
| 0769123894 | TYPE PLATE | Identification plate for transmission model |
| 0750100022 | SCREW PLUG | Seals hydraulic test ports on housing |
| 0636302602 | SCREW PLUG | Drain plug for piston chamber |
| 0634100633 | O-RING | Seals piston-to-housing interface |
| 4661301029 | NOZZLE | Oil jet for piston lubrication |
| 4661301027 | NOZZLE | Secondary oil jet for cooling |
