The drum clutch assembly is a core torque transfer unit in modern automatics (especially planetary-based designs). Key points:

1. Function – Houses stacked friction/steel plates activated hydraulically to lock planetary gearset elements.

2. Critical Parts – Drum body, apply piston, seals, return springs, and splined hubs (input/output connections).

3. Failure Modes

   • Drum cracks: Stress fatigue near weld seams or splines.

   • Seal leaks: Causes slow engagement (delayed shifts).

   • Plate wear: Glazing/burnt material leads to slippage (P0776 codes).

4. Inspection – Check drum for scoring/ovalization; measure plate clearance (exceeding 1.5mm requires pack replacement).