Audi E type clutch hub assembly ZF 8HP55A 38 spline and matching gears

Key Specifications:

1. Spline Design: 38 involute splines (12° pressure angle) with 0.8–1.2µm hardened surface finish for gear engagement

2. Material: Case-hardened 20MnCr5 steel (58–62 HRC core, 850HV surface)

3. Gear Match: Mated to planetary carrier with 0.02–0.05mm backlash tolerance

4. Critical Functions:

   • Transmits 320Nm in 2nd/4th/6th gears

   • Oil passages for clutch cooling (flow rate: 4–6 L/min)

5. Failure Modes:

   • Spline fretting (if backlash exceeds 0.1mm)

   • Lubrication starvation marks at >120°C

Note: Updated from 8HP45 with 15% wider spline base for 6000+ shift cycles. Requires ZF-approved friction modifier additives.