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.
Clutch Count Increases
| Clutch | Stock | Upgraded | Increase |
|---|---|---|---|
| A | 4 | 6 | +2 |
| B | 4 | 7 | +3 |
| C | 5 | 7 | +2 |
| D | 6 | 9 | +3 |
| E | 6 | 9 | +3 |
| F | 7 | 10 | +3 |
Combined with the FX-RT friction upgrade, the resulting torque-capacity increases are substantial.
Torque Capacity Gains (Per Gear)
Based on clutch engagement logic for the 9G and the combined friction + plate-count increases:
| Gear | Engaged Clutches | Torque Increase |
|---|---|---|
| 1st | B C E | +68% |
| 2nd | C D E | +68% |
| 3rd | B C D | +68% |
| 4th | B C F | +68% |
| 5th | B D F | +71.4% |
| 6th | D E F | +71.4% |
| 7th | B E F | +71.4% |
| 8th | A E F | +71.4% |
| 9th | A B F | +71.4% |
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.
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
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.















Reviews
There are no reviews yet.