Overview
The ZF 4616.120.008 PRESSURE REGULATOR is a precision hydraulic control component engineered specifically for the WG 65 series transmission. This OEM genuine part governs the modulation of hydraulic pressure within the valve body assembly, ensuring consistent clutch pack engagement and smooth gear transitions. As a critical element of the transmission’s hydraulic circuit, the 4616.120.008 directly influences shift quality and torque converter lock-up behavior. This pressure regulator is designed to maintain stable output pressures under varying load conditions, preventing erratic shifts and protecting internal seals from pressure spikes. When installed alongside a properly sealed TRANSMISSION HOUSING, this part forms the backbone of reliable hydraulic control in heavy-duty applications.
Symptoms of Failure
- Delayed or harsh gear engagement: When the 4616.120.008 wears, you may notice a pronounced lag when shifting from Neutral to Drive or Reverse, followed by an abrupt, jarring engagement. This occurs because the regulator can no longer modulate pressure rise smoothly.
- Intermittent transmission slipping under load: A failing pressure regulator often causes the transmission to slip during uphill climbs or when carrying heavy payloads. This symptom is frequently searched as “ZF transmission slipping under load” and indicates insufficient line pressure.
- Erratic shift patterns with flaring: You might observe RPM flare between gear changes, particularly during 2-3 and 3-4 upshifts. This happens when the regulator fails to maintain consistent pressure, allowing clutch packs to momentarily lose grip.
- Visible hydraulic fluid contamination: Metal particles in the transmission fluid or dark, burnt-smelling oil often accompany regulator failure. The worn spool valve inside the 4616.120.008 generates debris that circulates through the system.
Technical Specifications
| Specification | Value |
|---|---|
| Part Number | 4616.120.008 |
| OEM Reference | ZF 4616.120.008 |
| Material | Hardened steel spool with aluminum alloy body |
| Weight | 0.42 kg (0.93 lbs) |
| Overall Length | 85 mm |
| Spool Diameter | 18 mm |
| Operating Pressure Range | 5–22 bar |
| Seal Type | PTFE backup ring with O-ring |
Compatibility
This pressure regulator is primarily designed for the ZF WG 65 series transmission, which is commonly found in medium-duty trucks, buses, and construction equipment. Based on its hydraulic characteristics and mounting interface, the 4616.120.008 is also compatible with the WG 80, WG 120, and WG 150 series transmissions that share the same valve body architecture. It is not recommended for use in WG 180 or WG 200 models, which utilize a different pressure regulation system. For proper installation, this regulator must be secured using HEXAGON SCREW fasteners torqued to manufacturer specifications, and the surrounding HOUSING and HOUSING components should be inspected for wear during replacement.
Related Components
| Part Number | Name | Function |
|---|---|---|
| 4616101111 | TRANSMISSION HOUSING | Main structural casing that encloses all transmission components |
| 0636011118 | HEXAGON SCREW | Fastener for securing valve body and housing assemblies |
| 4616301304 | HOUSING | Intermediate housing section for clutch pack support |
| 4616301309 | HOUSING | Rear housing component for output shaft support |
| 0636011038 | HEXAGON SCREW | M8 fastener for transmission pan and valve body |
| 0636016015 | HEXAGON SCREW | M10 fastener for heavy-duty housing connections |
| 0631306085 | CYLINDRICAL PIN | Alignment pin for precise component positioning |
| 0634313118 | O-RING | Hydraulic seal for preventing fluid leakage |
| 0636304019 | SCREW PLUG | Threaded plug for sealing hydraulic passages |
| 0634801152 | SEALING RING | Copper washer for high-pressure sealing |
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