ACT 2006 Subaru Impreza HD-M/Perf Street Sprung Clutch Kit (6 SPD)
The ACT SB10-HDSS is the clutch most WRX STI owners end up with when the stock unit is worn out or starting to slip after an intake, exhaust and tune. It combines ACT's Heavy Duty pressure plate with its Performance Street sprung organic disc and adds Monoloc for the pull-type release, and it keeps the pedal close enough to stock that the car stays easy to drive every day. The listing says 2006 Impreza HD-M; the HD stands for Heavy Duty, the M for Monoloc, and the real fitment covers far more than one year.
The STI's 6-speed releases the clutch by pulling the diaphragm fingers toward the transmission. The factory setup holds the bearing to the pressure plate with a two-piece wedge collar and wire ring, and that joint is where trouble starts when pedal loads go up. ACT's Monoloc is a single hardened chromoly retainer that replaces both pieces and keeps the bearing square to the diaphragm, whatever the driver does with the pedal.
ACT rates SB10-HDSS at 522 ft-lb at the crank, 45 percent more than the factory clutch, which is plenty for a typical bolt-on STI. Clamp load comes from ACT's heat-treated Heavy Duty diaphragm, while the 240 mm (9.4 in) disc runs high-copper organic facings on a steel backing for heat transfer and burst strength, with a sprung hub and a reduced marcel for quicker shifts. ACT describes the feel as light to moderate pedal effort with smooth, positive engagement, and quotes 15 to 40 percent more pedal effort than stock for its Heavy Duty plates.
Clutch slip does not set a trouble code on a manual car, so do not wait for a check engine light to confirm it.
Check the clutch fluid level, look for leaks at the slave cylinder, and make sure the pedal comes all the way back up. Then run the high-gear load test: low rpm in 4th, full throttle, watch whether rpm rises faster than speed. Our guide to diagnosing slipping explains how to separate a true slip from other causes, and the flare versus slip article covers what each feels like from the seat. If a tune is already pushing past about 500 ft-lb at the crank, step up to the SB10-HDG6 6-pad kit instead.
ACT's chart lists SB10-HDSS for the 2004-2021 Subaru Impreza WRX STI and WRX STI with the 2.5L turbo EJ engine and 6-speed manual, including Limited, Special Edition, Launch Edition, Series.HyperBlue and Tsurugi models, plus the 2007-2009 Legacy GT spec.B and the JDM 2002-2005 Impreza WRX STI. It does not fit the 5-speed WRX. On a car with a swapped transmission, confirm the 1 in input spline and pull-type release before ordering, or send us year and VIN to check. More STI parts are in our rebuild kits and clutch section.
No flywheel comes in the kit. Resurface the factory flywheel or fit one of the two XACT flywheels ACT pairs with this kit, the 600235 Streetlite or the 600240 Prolite. Press in the new PB1004 pilot bearing, center the disc with the AT90 tool, and draw the pressure plate down evenly in a star pattern. Assemble the Monoloc exactly as the ACT sheet shows, bleed the hydraulics using the fluid named on the reservoir cap, and give the organic disc 300 to 500 miles of easy stop-and-go driving before hard launches.
| Brand | ACT |
| Part number | SB10-HDSS |
| Fits | ACT 2006 Subaru Impreza HD-M/Perf Street Sprung Clutch Kit (6 SPD) |
| Vehicle fitment | Subaru Impreza Hd-M/Perf (2006) |
| Type | Clutch Kits - Single |
| Condition | New |
| Ships | Same business day (in stock), from the USA |
| Warranty | 1-year |
ACT rates it at 522 ft-lb measured at the crank, 45 percent over the OE clutch. That covers most bolt-on and mildly tuned STIs.
Both use the same 3000503 sprung organic disc. SB10-HDSS uses the Heavy Duty SB019 plate with lighter pedal effort, while the XTSS uses the Xtreme SB019X plate for more clamp load and a heavier pedal.
No. It is for the 6-speed WRX STI and the 2007-2009 Legacy GT spec.B. The 5-speed WRX uses a different clutch.
No. Resurface your factory flywheel or add ACT's 600235 Streetlite or 600240 Prolite XACT flywheel, both listed by ACT for this kit.
ACT calls it light to moderate, and quotes 15 to 40 percent more pedal effort than stock for its Heavy Duty pressure plates depending on the car.
Yes. ACT recommends 300 to 500 miles of mild engagement, such as city driving, before racing or hard launches with an organic street disc.
