Function: Transmits engine torque to the planetary gearset via engaged clutch plates (typically 1st-3rd/4th gears).

Key Components:

• Input Shaft: Hardened steel with precision-ground splines (connects to torque converter)

• Clutch Drum: Aluminum/steel hybrid with laser-welded piston channel

• Integrated Piston: High-pressure seals (Vitron or HNBR) for rapid apply

Failure Modes:

• Spline Wear: Causes clutch drag (delayed engagement, P0776 codes)

• Drum Warpage: Overheating distorts sealing surface (>0.1mm runout = replace)

• Seal Extrusion: Contaminated ATF degrades seals → pressure loss

Critical Checks:

1. Measure shaft endplay (<0.3mm)

2. Verify drum concentricity (dial indicator test)

3. Inspect piston bore for scoring

Pro Tip: Pre-soak new clutch plates in ATF for 30 mins – dry plates cause initial shift flare.