Spool Performance – Mercedes 725 9G FX-RT Upgraded Clutch Kit 

 

Rated for up to 1,700 Nm input torque

The Mercedes 725 9G transmission is a strong unit from the factory—but once torque levels push past the mid-700 Nm, the stock frictions and limited plate counts begin to slip, especially under repeated high-load, high-temperature conditions.

Spool Performance has developed a complete upgraded clutch system for the 725 9G using our FX-RT high-coefficient, high-energy friction material, the same proven technology that transformed the 8HP50 platform into a competition worthy transmission.

This new kit increases both the coefficient of friction (+20%) and the clutch counts across all six elements, dramatically increasing the torque capacity of every gear.

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Clutch Count Increases

Combined with the FX-RT friction upgrade, the resulting torque-capacity increases are substantial.

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Torque Capacity Gains (Per Gear)

Based on clutch engagement logic for the 9G and the combined friction + plate-count increases:

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Final Torque Rating

The factory 725 9G is rated for 1000 Nm.
With the FX-RT clutch packs installed:

• 1st–4th gear clutch-limited rating: ≈1680 Nm

• 5th–9th gear clutch-limited rating: ≈1714 Nm

• Overall clutch-pack system capability: ≈1,700 Nm

This upgrade raises the clutch-limited torque threshold by +68–71%, depending on gear.

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Why FX-RT?

Our FX-RT friction material was engineered specifically for high-torque, high-energy, fast-shift transmissions. It has been proven in our 8HP50 kits, where customers reliably push 900–1000 Nm. Now the same technology elevates the Mercedes 725 9G into a new performance class.

Benefits include:

• 20% higher μ for dramatically improved static and dynamic holding power

• Higher thermal stability under repeated high-load upshifts

• Reduced shift flare and reduced clutch slip

• Smoother, more consistent clutch apply characteristics

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Who This Kit Is For

The Spool Performance 725 9G upgraded clutch kit is ideal for:

• High-power M177 builds

• GLE63 / GLS63 high-boost setups

• Tuned E63 / S63 running hybrid turbos

• Track-driven or heavy-use AMG applications

• Anyone targeting 1000+ crank hp with headroom

 

 

Your 725 9G is no longer the limiting factor. With Spool Performance FX-RT friction technology and increased clutch capacity, the transmission becomes capable of safely holding ~1700 Nm, giving your AMG the drivetrain headroom it needs to push big-power, high-boost builds confidently and repeatedly.

What’s Included

The Spool Performance 725 9G FX-RT Clutch Upgrade Kit includes all components required for a complete drop-in installation. No machining or custom fabrication is needed.

• Clutch A [B08] Pack (6-plate upgrade)

  • 6 x FX-RT friction discs

  • 6 x Upgraded Steel plates

  • 1 x Custom Pressure Plate

  Clutch B [B05] Pack (7-plate upgrade)

  • 7 x FX-RT friction discs

  • 7 x steel plates

  • 1 x Custom Pressure Plate

  Clutch C [B06] Pack (7-plate upgrade)

  • 7 x FX-RT friction discs

  • 7 x steel plates

  • 1 x Custom Pressure Plate

  Clutch D [K81] Pack (9-plate upgrade)

  • 9 x FX-RT friction+steel internal spline discs

  • 9 FX-RT friction+steel external spline discs

  • 1 x Custom Pressure Plate

  Clutch E [K38] Pack (9-plate upgrade)

  • 9 x FX-RT friction discs

  • 9 x steel plates

  • 1 x Custom Pressure Plate

  Clutch F [K27] Pack (10-plate upgrade)

  • 10 x FX-RT friction discs

  • 10 x steel plates

  • 1 x Custom Pressure Plate

Everything is pre-measured and packaged by clutch pack to ensure consistent clearances and simplified assembly. The kit is fully compatible with factory drums, pistons, and snap-ring locations.