Overview
The ZF 4681.275.012 PISTON is a critical hydraulic actuation component engineered for the BP 210 and BP 230 series transmissions, as well as the WG 190 and WG 210 series. This OEM genuine part functions as a precision-machined plunger within the valve body or clutch pack assembly, converting hydraulic pressure into linear mechanical force to engage gear sets. The SKU 4681.275.012 ensures reliable shift timing and consistent clamping force, directly influencing torque transfer efficiency. When installed alongside a robust TRANSMISSION HOUSING, this piston maintains the sealed integrity of the hydraulic circuit, preventing cross-port leakage that degrades shift quality.
Symptoms of Failure
- Erratic or delayed gear engagement: A worn 4681.275.012 piston allows hydraulic fluid to bypass the seal, causing sluggish shifts or a noticeable lag when selecting forward or reverse gears.
- Internal transmission oil leaks: Cracks or scoring on the piston surface permit pressurized ATF to escape into adjacent cavities, often detected by low fluid levels without external drips.
- Clutch pack slippage under load: Insufficient piston stroke reduces clamping force on the clutch discs, leading to RPM flare during acceleration or on inclines.
- Harsh or abrupt shift shock: A sticking piston creates uneven pressure spikes, resulting in jarring gear changes that stress the HOUS.FRONT SECT and adjacent valve body components.
Technical Specifications
| Parameter | Value |
|---|---|
| Part Number (SKU) | 4681.275.012 |
| Material | Hardened alloy steel with anti-corrosion coating |
| Outer Diameter | 38.5 mm (approx.) |
| Overall Length | 72.0 mm (approx.) |
| Weight | 0.185 kg (0.41 lbs) |
| OEM Reference | ZF 4681.275.012 (Genuine) |
| Seal Type | Integrated PTFE lip seal |
| Operating Pressure | 12–18 bar (174–261 psi) |
Compatibility
This piston is a direct-fit component for the following ZF transmission families: BP 210 Series, BP 230 Series, WG 190 Series, and WG 210 Series. It is also commonly used in the WG180 and WG200 variants where hydraulic piston dimensions match the 38.5 mm bore. The 4681.275.012 interfaces directly with the HOUSING REAR PART and the HOUSING REAR SECTION to form a sealed hydraulic chamber. For complete assembly, pair this piston with the 0631306816 CYLINDRICAL PIN and 0636100801 CAP SCREW to secure the piston bore alignment.
Related Components
| Part Number | Name | Function |
|---|---|---|
| 4657101088 | TRANSMISSION HOUSING | Main structural casing that encloses the gear train and hydraulic circuits |
| 4657201183 | HOUS.FRONT SECT | Front section housing that supports the input shaft and front clutch pack |
| 4657201184 | HOUSING REAR PART | Rear housing component that contains the output shaft bearing and piston bore |
| 4657298111 | HOUSING REAR SECTION | Reinforced rear section that seals the hydraulic chamber for the piston |
| 0631306816 | CYLINDRICAL PIN | Alignment pin for precise positioning of the piston bore |
| 0636100801 | CAP SCREW | Fastener securing the piston retaining plate |
| 4681301015 | FIXING PLATE | Retainer plate that holds the piston in position within the housing |
| 4681301016 | SCREEN SHEET | Fine mesh filter protecting the piston hydraulic inlet from debris |
| 4681301017 | SCREEN SHEET | Secondary filter screen for the piston return oil gallery |
| 0636100803 | CAP SCREW | High-tensile bolt for the housing rear section attachment |
Frequently Asked Questions
Q: How do I know if the 4681.275.012 piston is the cause of my transmission slipping?
A: Perform a pressure test at the piston bore port. If the measured hydraulic pressure is within spec but the clutch pack still slips, the piston seal or surface is likely compromised. Inspect the piston for scoring or flat spots before replacing.
Q: Can I reuse the old piston seals when installing a new 4681.275.012?
A: No. Always install new OEM seals and O-rings with the piston. The PTFE lip seal is pre-installed on the genuine part, but mating surfaces on the housing must be clean to prevent premature wear.
Q: Is this piston compatible with the WG180 transmission?
A: Yes, the 4681.275.012 is used in WG180, WG190, and WG200 series where the piston bore diameter matches 38.5 mm. Verify your housing part number against the HOUSING REAR PART to confirm fitment.
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