ZF 0501.321.426 PISTON for WG90/WG94 | OEM Genuine Part

Overview

The ZF 0501.321.426 PISTON is a critical hydraulic actuation component engineered for the WG90 and WG94 series transmissions. This OEM genuine part functions as a pressure-responsive plunger within the valve body or clutch pack assembly, converting hydraulic force into mechanical movement to engage gear sets. The SKU 0501.321.426 ensures precise fitment and material integrity, matching original factory specifications for reliable shift performance. This piston works in concert with the TRANSMISSION HOUSING to maintain proper fluid routing and pressure containment.

Symptoms of Failure

• Delayed or harsh gear engagement: A worn piston can cause sluggish shifting or abrupt clutch application, especially during cold starts.
• Internal transmission fluid leaks: Degraded piston seals allow pressurized oil to bypass, leading to low line pressure and visible drips near the HOUSING interface.
• Erratic shift patterns: The transmission may slip between gears or fail to hold a gear under load due to insufficient piston stroke.
• Overheating transmission fluid: Persistent piston leakage generates excess friction and heat, accelerating fluid degradation.

Technical Specifications

Compatibility

This piston is specifically designed for ZF WG90 and WG94 series transmissions, commonly found in medium-duty trucks, buses, and off-highway equipment. It also fits select variants of the WG180 and WG200 series where the valve body uses the same piston bore geometry. Always verify the TYPE PLATE on your transmission to confirm model compatibility. The piston interfaces with the TUBE for oil feed and is secured by a CYLINDRICAL PIN to prevent rotation during operation.

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