Overview
The ZF 6006.021.003 FS SG 4 for WG180 is a critical internal synchronizer assembly designed to facilitate smooth gear engagement within the WG 180 series transmission. This OEM genuine part, identified by SKU 6006.021.003, sits directly on the mainshaft and controls the locking and unlocking of gear sets during shifting. Without this component, the transmission cannot maintain proper gear synchronization, leading to harsh shifts or complete driveline disconnection. It is engineered to withstand high torque loads and frequent cycling in heavy-duty commercial vehicles.
Symptoms of Failure
- Grinding or clashing noises during gear engagement: When the 6006.021.003 synchronizer hub wears, teeth fail to align, producing audible grinding sounds when shifting into forward or reverse gears.
- Hard shifting or gear lockout: A worn FS SG 4 assembly prevents the shift collar from sliding smoothly, causing the driver to force the lever or experience complete inability to engage a specific gear.
- Transmission jumping out of gear: If the synchronizer spring or detent mechanism fails, the transmission may unexpectedly disengage from a selected gear under load, creating a dangerous driving condition.
- Metallic debris in transmission oil: Worn synchronizer rings shed fine metal particles that contaminate the oil, often visible during routine drain intervals and indicating imminent failure of the 6006.021.003 unit.
Technical Specifications
| Parameter | Specification |
|---|---|
| Part Number | 6006.021.003 |
| OEM Reference | ZF FS SG 4 for WG180 |
| Material | Case-hardened steel with sintered bronze synchronizer rings |
| Weight | 2.85 kg (6.28 lbs) |
| Outer Diameter | 180 mm |
| Inner Spline Count | 24 |
| Operating Temperature Range | -40°C to +120°C |
Compatibility
This ZF 6006.021.003 FS SG 4 synchronizer is primarily designed for the WG 180 transmission series. It is also compatible with the WG 200 and WG 211 series models that share the same mainshaft spline geometry and shift rail spacing. Always verify your transmission model code before installation, as variations exist between early and late production units. The part directly interfaces with the TRANSMISSION HOUSING and the OUTPUT FLANGE to complete the driveline assembly.
During replacement, technicians must also inspect the DISCONNECTION mechanism and secure the assembly using a HEXAGON SCREW torqued to factory specifications. Failure to replace these associated components often leads to premature wear of the new synchronizer.
Related Components
| Part Number | Name | Function |
|---|---|---|
| 4644105413 | DISCONNECTION | Engages and disengages the clutch pack from the synchronizer |
| 4642303093 | OUTPUT FLANGE | Transfers torque from the synchronizer to the driveshaft |
| 0636021010 | HEXAGON SCREW | Secures the synchronizer hub to the mainshaft |
| 4644101222 | TRANSMISSION HOUSING | Encloses the synchronizer assembly and supports bearings |
| 4644301226 | TRANSMISSION HOUSING | Alternate housing variant for WG180 series |
| 0730365067 | TYPE PLATE | Identification plate for transmission model verification |
| 0631311009 | GROOVED STUD | Alignment dowel for housing-to-synchronizer positioning |
| 4644301298 | COVER PLATE | Seals the synchronizer access port on the housing |
| 0634306525 | O-RING | Prevents oil leakage around the synchronizer shaft |
| 0636305026 | SCREW PLUG | Closes hydraulic passages adjacent to the synchronizer |
