ZF 4108.303.389 SUN GEAR for WG100/WG130/WG131 | OEM Genuine Part

Overview

The ZF 4108.303.389 SUN GEAR is a critical power-transfer component located within the planetary gearset of the WG100, WG130, and WG131 transmissions. As the central driving gear in the planetary assembly, it meshes directly with the planet gears to transmit torque from the input shaft to the output. This OEM genuine part, identified by SKU 4108.303.389, ensures precise tooth geometry and metallurgical integrity, which are essential for maintaining the high load capacity and smooth shifting characteristics of ZF’s heavy-duty powershift transmissions. The sun gear operates in close conjunction with the 4108302099: PLANET CARRIER and the 4108102042: INPUT shaft, forming the core of the gear reduction unit.

Symptoms of Failure

When the 4108.303.389 sun gear begins to wear, operators will notice distinct performance degradation. Look for these specific failure indicators:

• Transmission gear slipping under load: Worn or chipped sun gear teeth lose engagement with the planet gears, causing the transmission to momentarily lose power during acceleration or climbing.
• Metallic grinding or whining noise from the gearbox: Pitting or spalling on the sun gear’s tooth flanks generates a distinct high-pitched whine that increases with engine RPM.
• Contaminated transmission fluid with metallic debris: Flakes of hardened steel in the oil filter or drain plug indicate advanced sun gear wear, often accompanied by damage to the 4108301304: BEARING COVER.
• Erratic shifting or delayed engagement: Excessive backlash from a worn sun gear disrupts the timing of clutch packs, leading to harsh or delayed gear changes.

Technical Specifications

Compatibility

This genuine ZF sun gear is specifically engineered for the following transmission models: WG100, WG130, and WG131. It is also compatible with select variants of the WG180 and WG200 series that utilize the same planetary gearset architecture. Always verify the existing gear tooth profile and spline count before installation. When replacing this component, it is strongly recommended to also inspect the 4108101112: HOUSING and the 4108201177: HOUSING for wear, as debris from a failing sun gear often damages these mating surfaces. Additionally, replace the 0636302056: SCREW PLUG during service to ensure a proper seal.

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