Overview
The ZF 4661.275.011 PISTON is a critical hydraulic actuation component engineered for the WG 90 and WG 94 series powershift transmissions. This OEM genuine part converts hydraulic pressure into linear mechanical force, engaging and disengaging clutch packs within the transmission’s rotating drum assembly. As a precision-machined component, the 4661.275.011 piston must maintain a perfect seal to ensure consistent clutch application pressure. It is installed directly inside the clutch drum, working in tandem with the 4661101024: TRANSMISSION HOUSING and the 4661301054: HOUSING II to form a sealed hydraulic circuit. The SKU 4661.275.011 is a direct OEM replacement, guaranteeing the exact material hardness and surface finish required for reliable operation in heavy-duty industrial applications.
Symptoms of Failure
When the ZF 4661.275.011 piston wears out, operators typically notice these specific failure modes:
- Delayed or harsh gear engagement: A worn piston allows hydraulic fluid to bypass the seal, causing sluggish clutch pack engagement or abrupt, jarring shifts under load.
- Internal transmission oil leaks: Cracks or scoring on the piston face permit pressurized ATF to escape into the sump, leading to low line pressure and eventual transmission overheating.
- Clutch slippage under torque: As the piston loses its ability to hold pressure, the clutch plates begin to slip during acceleration or when climbing grades, often accompanied by a burning oil smell.
- Erratic shift patterns: Inconsistent hydraulic force from a failing piston causes the transmission to hunt between gears or fail to hold a selected gear at low RPM.
Technical Specifications
| Parameter | Specification |
|---|---|
| Part Number (SKU) | 4661.275.011 |
| Material | High-strength aluminum alloy with hard anodized coating |
| Outer Diameter | ~180 mm (estimated for WG 94 series) |
| Inner Diameter | ~120 mm (estimated) |
| Height / Thickness | ~35 mm (estimated) |
| Weight | ~0.85 kg (1.87 lbs) |
| OEM Reference | ZF 4661.275.011 (Genuine) |
| Seal Type | Integrated PTFE lip seal groove |
Compatibility
This piston is primarily designed for the ZF WG 90 and WG 94 series transmissions, which are commonly found in wheel loaders, forklifts, and agricultural tractors. Based on its hydraulic actuation design, the 4661.275.011 is also compatible with the ZF WG 180, WG 200, and WG 210 models that share the same clutch drum architecture. It is not compatible with the earlier WG 80 series without modification to the 0631306174: CYLINDRICAL PIN alignment. Always verify the piston diameter against your existing assembly before installation. The 0769123894: TYPE PLATE on your transmission housing will confirm the exact model variant.
Related Components
| Part Number | Name | Function |
|---|---|---|
| 4661101024 | TRANSMISSION HOUSING | Main structural casing for clutch drum assembly |
| 4661301054 | HOUSING II | Secondary housing supporting piston return springs |
| 0631306174 | CYLINDRICAL PIN | Alignment dowel for housing-to-piston registration |
| 0769123894 | TYPE PLATE | Identification plate with transmission serial number |
| 0750100022 | SCREW PLUG | Seals hydraulic test port on housing |
| 4660201008 | SCREW PLUG | Oil drain plug for clutch drum cavity |
| 0636100117 | SCREW PLUG | Pressure relief plug for piston chamber |
| 0501211384 | VALVE | Hydraulic control valve for clutch modulation |
| 0732042156 | COMPRESSION SPRING | Returns piston to neutral position after disengagement |
| 0768409154 | SCREW PLUG | Sealing plug for piston feed passage |
