Fitment

• Fits 1985-later GM 4L60/4L60-E 298mm units with 30-spline input shaft
• For 1982–1984 298mm units with 27-spline input shaft:
  • Converter and stator shaft must be updated to ’85-later design
• OE Cross References: 17803689, 08663580

Why You Need This Kit

The OE GM 4L60 series input housing is a known weak point and a leading cause of 3-4 clutch burnup in performance builds.
Problems with the OE design:

• Thin backing plate flexes under load
• Uneven heat build-up in a very limited clutch space
• Leads to premature 3-4 clutch failure

The Sonnax Smart-Tech® Input Housing solves this by:

• Making room for a physically larger, taller 3-4 clutch pack
• Using a strong, anchored backing plate to keep clutches parallel
• Dramatically increasing clutch capacity and reducing destructive heat

Key Features & Benefits

• Heavy Duty Input Shaft

  • High-strength, performance-ready shaft
  • Unique Sonnax design helping prevent stress crack failures
  • Housing and shaft also available separately

• Increased 3-4 Clutch Capacity
  Choose one of the following clutch configurations (both fit this housing):

  • Option 1: 8 frictions (.067") with 7 steels (.095")
  • Option 2: 9 frictions (.062") with 8 steels (.077")

• Anchored Backing Plate Design

  • Keeps clutches flat and parallel
  • Stops backing plate flex and distortion
  • Greatly reduces heat build-up and 3-4 failure

• Reinforced & Treated Housing

  • Specially treated housing is highly resistant to fatigue failure
  • Steel reinforcement sleeve prevents spline area breakage
  • Custom backing plate replaces OE retaining ring to eliminate blowout risk

• Premium Alto G3 Powerpack

  • Includes Alto High Performance G3 3-4 Powerpack clutches
  • Specifically engineered for the Sonnax Smart-Tech drum

Requirements & Compatibility Notes

This kit requires the following later-model components:

• ’91-later 3-4 apply ring
• ’97-later ring gear
• ’97-later stamped steel forward piston
• ’97-later dual-cage return spring

Not compatible with:

• Aluminum forward piston
• Sonnax billet forward piston 77764-01

For complete details, refer to the installation instructions.

Kit Contents

• Smart-Tech® Input Housing with 298mm Input Shaft Assembly
• PTFE-impregnated Rear Stator Support Bushing
• Input Drum Reinforcement Sleeve (installed)
• Overrun Piston
• Overrun Piston Inner Seal
• Overrun Piston Outer Seal
• 3-4 Clutch Apply Plate
• 3-4 Clutch Return Springs (10)
• Bolt-on Anchor Plate
• Socket Head Cap Screws (15)

Need a version separated from the shaft or housing only?
This Smart-Tech housing and heavy duty input shaft are also available individually.