Function: Engages overdrive (O/D) gear by applying hydraulic pressure to clutch pack in planetary transmissions (e.g., 4L60E, A340E).

Key Features:

• Material: Billet aluminum with micro-polished bore (surface finish Ra ≤0.8μm)

• Seal Design: Dual-lipped HNBR or Viton for high-temp stability (>250°F)

• Bleed Circuit: Quick-release channels prevent clutch drag

Failure Modes:

• Seal Roll-Over: Improper installation causes pressure leaks (O/D slippage)

• Bore Scoring: Contaminants jam piston (delayed O/D engagement)

• Fatigue Cracks: Stress fractures near apply lugs (sudden O/D loss)

Critical Specs:

1. Piston-to-bore clearance: 0.03-0.07mm

2. Apply pressure: 55-85 psi (varies by transmission)

Pro Tip: Lubricate seals with petroleum-free grease during assembly – petroleum degrades rubber.