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1.58 Ratio Extreme Planetary Assembly Kit
Part No. 28158G-06SP

View Instructions

Engine power and RPM continue to increase, creating the need for different transmission and axle ratios to get the car down the track as quickly as possible. The innovative Sonnax 1.58 ratio Extreme planetary assembly kit 28158G-06SP 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 different transmission.

Extreme planetary assemblies from Sonnax include Advanced Process sun gears and pinions made to the same exacting standards used on Formula 1, Nascar and other high-end professional racing circuits. Advanced Process parts undergo an additional three-step process that allows for greater durability and higher levels of performance. These units are fully assembled and ready to install.

  1. Cryogenic tempering to ultra-low temperatures (-350°F) for an even denser, more uniform gear with a tough and wear-resistant structure.
  2. Shot peening for increased gear resistance to fatigue failure, cracking or galling.
  3. Super-finish to reduce friction, vibration, noise and wear on the gear, potentially tripling the life of the part.

The 1.58 assembly's front and rear sun gears undergo an additional Dry Film Lubricant (DFL) treatment to reduce spalling and improve longevity. The carrier also includes high strength steel/bronze/PTFE-coated rear sun gear washer and pinion thrust washers.

  • High-strength 300M output shaft with “rolled splines” to prevent spline twist
  • Direct replacement, requires no special assembly or case modification
  • Sonnax Extreme 9310 Advanced Process gears
  • Bolt together carrier for ease of service
  • High capacity reverse clutch assembly included

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

Requires one of the following Sonnax 24-tooth high gear clutch drums: 28756-01, 28756-08, 28756-01K, 28756-08, 28756-15K or 28756-16K.

  • Gear Process Level: Extreme
  • Material: 300M Rolled Spline
  • Shaft Length Option: Short
  • Flange Tooth Count: 24
  • Ratio: 1.58

May 09, 2017

From the Bench: Building a World‑Class Powerglide Racing Transmission

Gregg Nader

Topics: Diagnostics And Theory Transmission GM Powerglide Transmission

Watch Now

  • 28158g 06sp