4L65E Mechanical Oil Pump Assembly 1998 - 2003 300mm

Typical Faults:

1. Crescent Wear

   • Symptom: Low line pressure (P0756/P0776 codes, delayed shifts)

   • Cause: Abrasives score pump face (especially after torque converter failure)

2. Drive Gear Spline Stripping

   • Symptom: No movement in any gear (metal debris in pan)

   • Cause: Torque converter hub wear transfers to pump

3. Pressure Regulator Sticking

   • Symptom: Erratic shifts or harsh engagements

   • Trigger: Varnish buildup from degraded Dexron III

Critical Measurements:

• Rotor Clearance: >0.15mm requires replacement

• Prime Test: Should hold 50+ psi for 10+ seconds

Pro Tip: Always replace pump and TC together – 85% of pump failures originate from converter debris.