The Sonnax Smart-Tech® Big Input Shaft and Converter Combo Kit is a complete, matched solution designed to eliminate input shaft spline twist, breakage, and torque converter compatibility issues in high-torque Chrysler 47RH, 47RE, and 48RE diesel applications.
At the core of this system is the Sonnax Smart-Tech Big Input Shaft Kit, part number 22121B-08K. Compared to the strongest 300M 23-spline shafts, the Sonnax 35-spline input shaft is 35% stronger at both the spline section and the sealing ring and cross-hole area, addressing the most common failure points seen in high-torque diesel applications.
The larger diameter sealing ring and cross-hole area require a custom stator and pump cover assembly, which is included in this kit. The stator assembly features standard 48RE tube splines manufactured from high-strength steel, improved retention in the stator body, 48RE-matched pump porting, and special rubber seals that eliminate oil leakage between the pump body and cover.
The extended direct clutch hub portion of the input shaft allows the use of an additional OE-thickness direct friction plate when paired with the included thinner billet aluminum direct piston. This increases clutch capacity from five to six frictions while retaining OE-thickness steels, backing plate, waved retaining ring, and proper clutch clearances.
Many aftermarket solutions attempt to increase clutch count by reducing steel thickness or eliminating the waved retaining ring, which reduces heat capacity and contributes to excess 2-3 shift overlap. The Sonnax system avoids these compromises by increasing friction count while preserving steel mass and OE clutch geometry for the optimal balance of capacity, durability, and shift quality.
- Extreme-duty 1-1/8" diameter 35-spline input shaft
- .100" larger diameter at sealing ring and cross-hole area
- One-piece ultra high-strength 300M steel forging
- OE-style through-holes and cross holes for proper oil flow
- Custom stator and pump cover assembly for long-term durability
The Converter
This combo kit includes a SunCoast 35-spline torque converter engineered specifically to work with the Sonnax Smart-Tech Big Input Shaft system. Using a matched converter eliminates compatibility issues and ensures proper torque transfer, lockup function, and long-term reliability.
SunCoast Dodge-series torque converters are designed, machined, and assembled in house, allowing precise control over stall speed, torque multiplication, and overall efficiency. Multiple billet stator options are available to tailor stall characteristics to the vehicle’s power level and intended use.
The converter features a CNC-machined billet stator that improves torque multiplication and efficiency prior to lockup. A CNC-machined billet piston houses a multi-disc lockup clutch pack and resists flex under high load, while lockup apply is made directly to a forged billet cover for consistent and reliable clutch engagement.
- 35-spline torque converter matched to Sonnax Big Input Shaft
- Multiple billet stator options for variable stall speeds (1800–3000 RPM stocked)
- Custom pump and turbine modifications performed in house
- TIG-welded, furnace-brazed fins for added strength
- Proprietary multi-disc lockup clutches with trapezoid clutch teeth
- CNC-machined billet stators and pistons
- 4140 heat-treated turbine splines matched to application
- Forged billet cover for high-torque durability
- Pressure-tested welds and precision spin balancing
Together, the Sonnax Smart-Tech Big Input Shaft and SunCoast 35-spline torque converter form a complete, engineered system designed to handle increased torque while maintaining proper oil flow, clutch durability, and consistent lockup performance.
