Overview
The ZF 4644.330.373 DIAPHRAGM is a critical pneumatic actuation component engineered specifically for the WG 201 Series transmission. This OEM genuine part, identified by SKU 4644.330.373, functions as a flexible sealing membrane within the clutch or shift actuator assembly. It isolates air pressure chambers while transmitting linear force to engage gear sets, ensuring precise modulation of hydraulic circuits. Without this diaphragm, the transmission cannot maintain the necessary pressure differentials for smooth shifting under load. It is a direct replacement for worn units in the WG201, WG180, and WG200 families.
Symptoms of Failure
When the ZF 4644.330.373 diaphragm deteriorates, operators typically encounter these specific failure modes:
- Erratic or delayed gear engagement: A cracked or stretched diaphragm cannot hold consistent air pressure, causing hesitation when shifting from neutral to drive or between forward gears.
- Audible air hissing from the actuator housing: Perforations in the rubber membrane allow compressed air to escape, producing a distinct leak sound near the transmission bell housing.
- Oil contamination in pneumatic lines: A ruptured diaphragm permits transmission fluid to migrate into the air system, visible as oil mist from breather ports or wetness on the TRANSMISSION HOUSING.
- Intermittent loss of torque converter lockup: Insufficient diaphragm stroke prevents full clutch pack engagement, leading to elevated transmission temperatures and reduced fuel efficiency.
Technical Specifications
| Parameter | Specification |
|---|---|
| Part Number | 4644.330.373 |
| Material | Nitrile rubber (NBR) with fabric reinforcement |
| Outer Diameter | 120 mm (4.72 in) |
| Thickness | 4.5 mm (0.177 in) |
| Operating Pressure Range | 6 – 12 bar (87 – 174 psi) |
| Temperature Range | -40°C to +120°C (-40°F to +248°F) |
| Weight | 0.085 kg (0.187 lb) |
| OEM Reference | ZF 4644.330.373 |
Compatibility
This diaphragm is a direct fit for the following ZF transmission series: WG180, WG200, WG201, and WG210. It is commonly used in off-highway vehicles such as wheel loaders, graders, and dump trucks. When replacing this part, always inspect the mating TRANSMISSION HOUSING for scoring or corrosion that could damage the new diaphragm. Additionally, verify the condition of the THREADED BUSH and SCREW PLUG in the actuator port, as these sealing interfaces are critical for leak-free operation.
Related Components
| Part Number | Name | Function |
|---|---|---|
| 4644101160 | TRANSMISSION HOUSING | Main structural casing for gear and actuator assembly |
| 4644301323 | TRANSMISSION HOUSING | Alternate housing variant for WG201 series |
| 4644301189 | THREADED BUSH | Provides wear-resistant thread for actuator mounting bolts |
| 4475280043 | SCREW PLUG | Seals oil passages in the housing |
| 0634306198 | O-RING | Static seal between diaphragm and housing flange |
| 0730365067 | TYPE PLATE | Identification plate for transmission model |
| 4644301161 | COVER PLATE | Protects diaphragm from debris ingress |
| 0636100621 | HEXAGON SCREW | Fastener for cover plate attachment |
| 0631610020 | SET SCREW | Adjustment screw for actuator stroke calibration |
| 0501218540 | BREATHER | Equalizes pressure inside the actuator housing |
