ACT Heavy Duty Performance Street Sprung Clutch Kit w/ Monoloc - 2004-2021 Subaru WRX STI (SB10-HDSS)

The Gold Standard for Track & Daily STI Builds
The ACT Heavy Duty Performance Street Sprung Clutch Kit (SB10-HDSS) is the ultimate clutch upgrade for the 2.5L EJ257-powered Subaru WRX STI. Purpose-built to handle aggressive street driving, heavy bolt-ons, and upgraded flex-fuel maps, this single-disc kit safely supports an impressive 522 ft-lbs of torque at the crank (a 45% increase over original equipment). Despite its massive clamping capacity, it maintains a light-to-moderate pedal effort and smooth, chatter-free engagement that won't punish your leg during stop-and-go daily traffic.

The Pull-Type Fix: Patented Monoloc Technology
Factory Subaru STI 6-speeds utilize a pull-type clutch system notorious for wedge-collar separation and alignment issues under hard abuse. ACT solves this problem permanently by including their patented Monoloc collar. The Monoloc is a hardened chrome-moly steel, one-piece direct replacement for the failure-prone OEM two-piece wedge collar and wire ring. It ensures uniform loading on the throwout bearing and pressure plate for flawless alignment and crisp, high-RPM shifts, no matter how hard you drive.

Like all ACT kits, the heavy-duty pressure plate features a four-stage heat-treated diaphragm spring for uniform clamp load and zero high-RPM deflection, and the complete assembly is computer-balanced for buttery smooth operation up to redline.

• Street-Focused Drivability: The premium organic, full-face sprung hub disc delivers incredibly smooth, positive engagement with predictable, manageable control.
• Burst-Proof Strength: A high copper-content friction lining backed by steel plates optimizes heat dissipation and ensures maximum durability under heavy thermal loads.
• Patented Monoloc Collar: Eradicates the classic pull-type clutch separation issue for total peace of mind on hard launches.
• Direct Fitment: Reuses your factory STI flywheel or pairs perfectly with an ACT Streetlite or Prolite replacement.

Technical Specifications:

• Part Number: SB10-HDSS
• Torque Capacity: 522 ft-lbs (At Crank)
• Torque Capacity Over OE: +45%
• Disc Style: Full Face Performance Organic Street Disc
• Hub Style: Spring-Centered / Sprung Hub
• Disc Diameter: 240mm (9.4 in.)
• Spline Count / Input Shaft: 24-Spline / 1.000 in.
• Pressure Plate Type: Heavy Duty
• Release Collar Upgrade: Patented ACT Monoloc Collar Included
• Product Total Weight: 18.2 lbs.

Fitment:

• Subaru WRX STI / Impreza WRX STI (USDM & Canadian Markets): 2004–2021 (2.5L Turbo 6-Speed Manual)
  • Compatible with all trim levels: Base, Limited, Special Edition, Launch Edition, Series.HyperBlue, Type RA, S209, Sport, Sport-tech, Tsurugi Edition, and Kanrai Edition.
• Subaru Legacy GT spec.B: 2007, 2008, 2009 (2.5L Turbo 6-Speed Manual)
• Subaru Impreza WRX STI [JDM Models Only]: 2002, 2003, 2004, 2005 (2.0L Turbo 6-Speed Manual)

Fitment Warning for Legacy GT Owners: While this kit fits the 6-speed transmission found in the 2007–2009 Legacy GT spec.B, it requires upgrading to an STI-style flywheel for proper height and clutch engagement.

STI vs. WRX Clutch Selection: This SB10-HDSS is engineered strictly for the specialized Pull-Type 6-speed transmission found in USDM STI models. If you drive a standard USDM 5-speed or 6-speed WRX (2006–2026+), this kit will not fit your transmission. You will instead need the ACT SB11-HDSS Clutch Conversion Kit, which features a Push-Type configuration and includes a matching conversion flywheel.

The Nameless "Installation" Pro-Tip:

The Break-In Rule is Law: To prevent glazing and premature failure, a full-face organic street disc requires a strict 500-mile break-in period consisting of normal stop-and-go city driving. Avoid dyno sessions, hard pulls, aggressive downshifts, or high-RPM slips during this window. Letting the friction materials evenly seat against the mating surfaces guarantees a long, silent, slip-free life.

Flywheel Notice: Unlike the WRX SB11 package, this kit does not include a flywheel out of the box. You can choose to machine and resurface your factory OEM STI flywheel, or take this opportunity to drop in a lightweight ACT Streetlite (600235) or ACT Prolite (600240) chromoly flywheel to get blistering, rev-happy throttle response!