Function: Transmits torque in forward gears (1st-4th) via multi-plate clutch engagement in Nissan/Infiniti transverse 6-speeds.

Key Components:

• Splined Input Shaft: Hardened steel with micro-polished bearing surfaces.

• Clutch Drum: Laser-welded aluminum with reinforced piston lugs (OEM 31706-JK00B).

• Piston Assembly: Dual-lipped seals for high-pressure stability (60-80 psi apply).

Failure Modes:

• Spline Wear: Causes clutch drag (delayed 1-2 shifts, P17F5 codes).

• Seal Extrusion: Contaminated ATF (NS-3) degrades seals → pressure loss.

• Drum Cracks: Thermal stress near weld seams (sudden no-drive condition).

Critical Checks:

1. Shaft endplay (<0.2mm).

2. Drum runout (<0.08mm).

Pro Tip: Replace both C1 clutch and torque converter if metal debris is present – debris migrates to TC lockup clutch.