Overview
The ZF 4699.025.055 GP25 is a genuine OEM clutch piston assembly engineered for the internal hydraulic actuation system of heavy-duty ZF transmissions. This component is critical for modulating oil pressure to engage and disengage gear sets within the transmission housing. As a direct OEM replacement, the SKU 4699.025.055 ensures precise fitment and material integrity, preventing cross-contamination of hydraulic circuits. It sits directly within the valve body or clutch drum assembly, converting pilot pressure into linear force for clutch pack compression. Utilizing this genuine part maintains the original transmission calibration and avoids premature wear associated with aftermarket alternatives.
Symptoms of Failure
When the ZF 4699.025.055 GP25 piston assembly degrades, operators will notice distinct operational issues. Delayed or harsh engagement between forward and reverse gears is a primary indicator, often accompanied by a momentary loss of power during shifting. Internal hydraulic leakage occurs as the piston seals wear, leading to low line pressure and transmission overheating under load. A persistent grinding noise during gear changes, particularly in lower ranges, signals that the piston is not fully releasing the clutch pack. Finally, erratic shift patterns where the transmission hunts for gears or fails to hold a selected gear under heavy torque demand are common failure symptoms of a worn GP25 assembly.
Technical Specifications
| Specification | Detail |
|---|---|
| Part Number / SKU | 4699.025.055 |
| OEM Reference | ZF GP25 (Genuine Piston) |
| Material | Hardened Aluminum Alloy with Nitrile Seals |
| Outer Diameter | 155 mm (approx.) |
| Inner Diameter | 95 mm (approx.) |
| Overall Height | 42 mm (approx.) |
| Weight | 0.85 kg (1.87 lbs) |
| Operating Pressure | 12-18 bar (174-261 psi) |
| Seal Type | Double Lip PTFE-Energized |
Compatibility
This GP25 piston assembly is specifically designed for ZF’s modular transmission series used in construction machinery. It is a direct fit for the ZF WG180 and ZF WG200 series transmissions, which are common in wheel loaders, telehandlers, and graders. The part also cross-references with certain variants of the ZF 4WG-200 and ZF 6WG-250 transmissions, particularly those with hydraulic clutch packs requiring a 155mm piston bore. For applications in ZF Ergopower or ZF Ecomat series, verify the clutch drum depth, as the 4699.025.055 is optimized for the standard construction machinery clutch pack stack height. Always confirm your transmission serial number against the OEM parts catalog before installation.
