6R80 CVT Automatic Transmission Direct Gear "B" Clutch Drum Assembly

Typical Faults:

1. Spline Stripping

   • Symptom: Slippage in direct gear (P0733/P0776 codes)

   • Cause: Hardened steel splines wearing against aluminum drum

2. Piston Bore Scoring

   • Symptom: Delayed 3-4 upshift

   • Trigger: Contaminated ATF acting as abrasive

3. Drum Cracking

   • Symptom: Sudden loss of drive (metal debris in pan)

   • Root Cause: Thermal fatigue near lubrication ports

Critical Checks:

• Spline Engagement: Should have <0.1mm rotational play

• Bore Diameter: Measure at 3 points (taper >0.03mm fails)

• Drum Runout: >0.05mm requires replacement

Pro Tip: Use assembly lurbe on splines during rebuild – dry starts accelerate wear