1.58 Ratio Extreme Planetary Assembly Kit
Part No. 28158G-NS

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Sonnax offers complete GM Powerglide planetary assemblies in a variety of gear set options and configurations to ensure you get the performance you want without overpaying or sacrificing quality. Each comes fully assembled and ready to install.

Track-proven to 3,000 HP, Sonnax Extreme planetaries are the finest quality Powerglide planetary assemblies in the world. From carrier and output shaft to gears and thrust washers, every component is refined for maximum durability in the most demanding applications. The ring gears are even pre-drilled for the Sonnax stabilizer system to prevent vibration and broken reverse friction plates. Extreme gear sets feature Sonnax premium sun and pinion gears that also undergo the same advanced processing used in Formula 1, NASCAR® and other high-end professional racing circuits.

1.58 ratio Extreme planetary assembly kit 28158G-NS delivers tunable control right at the start, when traction can make or break a race. The one-of-a-kind Sonnax 1.58 is designed to fit into existing Powerglide cases, allowing racers to achieve the lowest numerical ratio available for the Powerglide without the hassle and expense of converting to a TH400. This kit is compatible with all Sonnax extreme duty input shafts, although it's primarily for use when building a big input shaft system.

  • Includes all the same parts found in complete Sonnax 1.58 assembly kits, minus the output shaft, rear sun gear and washer that must be purchased separately when building a big shaft system
  • Direct replacement, requires no special assembly or case modification
  • Top-quality sun and pinion gears undergo additional advanced processing for unmatched durability
  • Includes high-capacity reverse clutch assembly
  • 24-Tooth billet drum flange designed to work exclusively with Sonnax clutch drums
  • Bolt-together carrier for ease of service

See chart and specs below to determine if this planetary assembly suits your application, or dial in options here to choose your build.


Track-Proven to 2,000 HP


Track-Proven to 3,000 HP

Sonnax Warranty 2 Years (Gears Only) 2 Years (Gears & Shaft)
Gear Material 9310 Suns & Pinions 9310 Suns & Pinions
Gear Process Premium
Advanced (Learn More)
Shaft Material 4340 300M
Shaft Splines Cut Spline Rolled Spline
Drum Flange 12-Tooth 24-Tooth
Ring Gear Standard Maximum Duty

Applies to planetary assembly kits only

The Sonnax big shaft system for Powerglides requires changing to a 35-spline turbine hub.

  • Gear Set
  • Sun Gear & Drum Flange 24-Tooth
  • Ring Gear
  • Reverse Clutch Piston with Seals 2 Seals
  • Reverse Clutch Piston Plate
  • Reverse Clutch Pressure Plate
  • Reverse Clutch Frictions (7)
  • Reverse Clutch Steels (8)
  • Gear Process Level: Extreme
  • Ratio: 1.58
  • Flange Tooth Count: 24

  • Powerglide 1.58 Ratio Extreme Planetary Assembly Kit 28158G-NS


From the Bench: Building a World‑Class Powerglide Racing Transmission
Eliminate Powerglide Input Shaft Failure with the Sonnax Big Shaft System

The 1.58 gear set has had a significant impact on helping my racing program this year and played a big part in our being able to win two races and be more competitive. It has enabled us to have a much greater tuning window and allowed us to apply the power from the engine more efficiently. The 1.58 has over 50 passes on it and is still going strong. Thank you to Sonnax for making such a great product and for developing new transmission parts so that we as racers can continue to improve and go faster.

K. Ashley Kevin Ashley Racing Newark, DE