4R70W 4R75E CVT Transmission Forward Clutch Drum With Solid Shaft

Typical Faults:

1. Spline Wear at Shaft-Drum Interface

   • Symptom: Delayed forward engagement (P0776 codes)

   • Cause: Micro-movement from torque reversals

2. Drum Warpage

   • Symptom: Harsh 1-2 shifts or clutch drag

   • Trigger: Overheating (>300°F) distorts sealing surface

3. Piston Seal Extrusion

   • Symptom: Pressure loss in forward gears only

   • Root Cause: Contaminated ATF degrading seal material

Critical Measurements:

• Shaft Runout: >0.05mm requires replacement

• Drum-to-Piston Clearance: 0.10-0.15mm (use feeler gauge)

• Seal Groove Wear: >0.2mm depth = rebuild

Pro Tip: Always replace shaft and drum as matched set – mismatched splines accelerate wear.