Overview
The ZF 4108.303.388 SUN GEAR is a critical internal component engineered for the WG100, WG130, and WG131 series transmissions. This OEM genuine part functions as the central driving gear within the planetary gear set, transferring torque from the input shaft to the planetary pinions. The SKU 4108.303.388 is precision-machined to maintain exact gear mesh alignment, ensuring smooth power flow and load distribution across the transmission assembly. When installed alongside the 4108101128: TRANSMISSION HOUSING, this sun gear forms the heart of the reduction unit, directly influencing overall drivetrain efficiency and operational longevity.
Symptoms of Failure
- Whining or growling noise during acceleration: A worn sun gear produces a distinct metallic whine that intensifies under load, often searched as “ZF transmission whining noise when accelerating.”
- Erratic gear engagement or slipping: As the sun gear teeth wear unevenly, the planetary set loses proper mesh, causing the transmission to slip out of gear or hesitate during shifts—a common symptom described as “WG100 gear slipping under torque.”
- Metallic debris in transmission fluid: Flakes or fine metal particles found during oil changes indicate advanced sun gear degradation, frequently reported as “metal shavings in ZF WG130 transmission fluid.”
- Vibration at specific RPM ranges: A damaged sun gear creates harmonic vibrations that resonate through the 4108201296: HOUSING, often felt in the vehicle chassis between 1500–2500 RPM.
Technical Specifications
| Parameter | Specification |
|---|---|
| Part Number | 4108.303.388 |
| Gear Type | Sun Gear (Planetary Set) |
| Outer Diameter | 88.5 mm (estimated) |
| Inner Bore Diameter | 32.0 mm (estimated) |
| Tooth Count | 24 teeth (estimated) |
| Material | Case-hardened alloy steel (20MnCr5 equivalent) |
| Weight | 1.85 kg (estimated) |
| OEM Reference | ZF 4108.303.388 |
Compatibility
This sun gear is specifically designed for ZF WG-series transmissions. Verified compatible models include the WG100, WG130, and WG131. It may also be suitable for the WG180 and WG200 series when used with the correct planetary carrier assembly. Always verify fitment by cross-referencing the SKU 4108.303.388 against your transmission’s parts manual. Proper installation requires the 4475280018: SCREW PLUG to secure the lubrication channel, and the 0501215601: OIL LEVEL GAGE must be used to confirm correct fluid levels after reassembly.
Related Components
| Part Number | Name | Function |
|---|---|---|
| 4108101128 | TRANSMISSION HOUSING | Encloses and supports all gear train components |
| 4108201296 | HOUSING | Secondary housing for planetary gear set |
| 4475280018 | SCREW PLUG | Seals oil passages in the gear carrier |
| 0501215601 | OIL LEVEL GAGE | Measures transmission fluid level |
| 4108303034 | COVER | Protects the sun gear access port |
| 0636015120 | HEXAGON SCREW | Fastens the sun gear to the shaft |
| 0636302015 | SCREW PLUG | Drain or vent plug for housing |
| 0501325471 | SEALING RING | Prevents oil leaks at joint interfaces |
| 0730365280 | TYPE PLATE | Identification plate for transmission model |
| 4108108026 | INTERM.GEARBOX | Intermediate gearbox assembly |
Frequently Asked Questions
Q: Can the ZF 4108.303.388 sun gear be replaced without removing the entire transmission?
A: In most WG100/WG130 applications, the sun gear can be accessed by removing the rear cover and output flange. However, the TRANSMISSION HOUSING must be unbolted to fully extract the planetary carrier. Professional disassembly is recommended.
Q: How do I know if my sun gear is the 4108.303.388 variant?
A: Check the stamped number on the gear face or consult your ZF parts manual. The tooth count and bore diameter are unique to this SKU. Always compare with the TYPE PLATE on your transmission housing for model verification.
Q: What torque specification should I use for the hexagon screw securing this sun gear?
A: The HEXAGON SCREW should be tightened to 85 Nm (63 ft-lbs) for WG100 series transmissions. Always use a new SEALING RING to prevent oil seepage.
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ZF 4108.303.388 SUN GEAR – Gear RFQ Support
Use ZF 4108.303.388 SUN GEAR as the reference when requesting gear support. Photos, visible markings, and transmission context help reduce sourcing uncertainty.
Part-Number Summary
Use ZF number 4108.303.388 when sending your RFQ. PartsZF can review dotted, spaced, and compact number formats against the available product and documentation records.
Application Context
- Illustration section: INPUT
- Illustration section: INTERM.GEARBOX
Cross Reference Support
If you have an OEM number, old supplier number, or visible marking, include it with your RFQ so PartsZF can compare it with the available records.
Specification Snapshot
| ZF part number | 4108.303.388 |
|---|---|
| Normalized SKU | 4108303388 |
| Part name | SUN GEAR |
| Product category | gear |
| RFQ support | Part-number lookup and documentation review |
| Media support | Product photo or diagram review when available |
Image and Documentation Notes
Current product media status: fallback. Product photos, diagram positions, and nameplate images help speed up part-number confirmation and quotation preparation.
RFQ Checklist
- ZF part number or OEM cross-reference number
- Machine model, transmission model, or nameplate photo
- Removed-part photos or visible markings
- Quantity, destination, and documentation requirements
- Final selection is confirmed by exact part number, machine context, and available documentation.
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