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

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Spool Performance's FX-RT clutch upgrade kit is designed for the Mercedes-AMG 725 Series 9G-Tronic transmission, with the aim of significantly increasing torque delivery in high-performance M177 engine projects. The kit is based on Spool's own FX-RT friction material and an increased number of clutch plates in all six clutch packs. The end result is that the transmission's torque delivery is increased to around 1,700 Nm , while maintaining a controlled shift feel and OEM compatibility.

Performance and torque endurance

The Mercedes 725 9G transmission is strong as standard, but at torques above ~700 Nm, the OEM clutches start to slip, especially under repeated heavy loads and high oil temperatures.

The Spool FX-RT series solves this:

• +20% higher friction coefficient

• Increased number of plates in all clutch packages

• Torque endurance up to ~1,700 Nm

Increase in torque duration depending on the gear:

• 1–4 gears: approx. +68%

• 5–9 gears: approximately +71%

Factory estimate for 725 transmission is ~1000 Nm → with FX-RT upgrade approximately 1680–1714 Nm clutch limited capacity .

Clutch kit updates

The increased friction surface distributes the load more evenly and improves thermal management.

Advantages of FX-RT friction material

FX-RT is designed specifically for high torque and fast shifting automatic transmissions.

• 20% higher μ → better grip

• Better thermal stability during hard driving

• Less slippage and shift flare

• Smoother and more controlled engagement

• Proven performance in racing use of the 8HP series

Series content

Complete drop-in kit, no machining.

• Clutch A pack (6-disc)

• Clutch B pack (7-disc)

• Clutch C pack (7-disc)

• Clutch D pack (9-disc)

• Clutch E pack (9-disc)

• Clutch F pack (10-disc)

• FX-RT friction plates and steel plates

• Custom pressure plates

• Pre-sized switch packages

Compatible with OEM drums, pistons and snap-ring solutions.

Who is this series for?

• M177 engine projects over 1000 hp
  

• AMG track cars

• High-boost setups

• Racing and drag builds

When engine power increases significantly, the transmission is no longer a limiting factor.

Technical benefits

• Torque endurance up to ~1,700 Nm

• Better temperature resistance

• Less slippage and wear

• OEM compatible installation

• Smooth and controlled shifting feel

Fitment

Mercedes-AMG 725-series 9G-Tronic-gearbox mm:

• AMG C63 / C63 S

• AMG E63 / E63 S
  

• AMG CLS63

• AMG GLE63 / GLS63

• AMG S63

and other M177-engine equipped AMG models.