ACT 13-23 Subaru WRX Mod-Twin 225 HD Sprung Street Clutch Kit

A tuned WRX that is still a daily driver puts a clutch in a tough spot: it needs to hold boost-driven torque, but it also has to idle through traffic and leave a stop without shaking the AWD driveline. ACT T1SS-S01, the Mod-Twin 225 Heavy Duty Sprung Street kit, is ACT's twin disc built for exactly that job on the 2013-2023 Subaru WRX. ACT rates it at 625 ft-lb at the crank, 99 percent more than the original clutch, with a light pedal and smooth street engagement.

What the Mod-Twin 225 HD does in a WRX

Holding power comes from doubling the friction surface rather than from a brutal pedal. Two 225 mm (8.8 inch) steel-backed organic friction plates sit on either side of a floater, so the clamp load works across twice the area inside a package that fits the WRX bellhousing. Both friction plates drive one sprung Mono-Drive hub. That single spring center is the key detail on an AWD car: it soaks up torsional vibration before it reaches the input shaft, center differential and axles, which ACT says extends input shaft life.

This version uses ACT's Heavy Duty diaphragm rather than the Xtreme spring, so pedal effort stays closer to stock. The cover is forged aluminum, the assembly is SFI 1.2 certified, and the design is modular: the hub, plates and floater can be replaced individually later (ACT sells the sprung hub on its own as 7830218P). In the kit ACT includes a CNC-machined, balanced flywheel, the pressure plate cover, diaphragm, face, friction plates, sprung Mono-Drive hub, floater, Monoloc collar, release bearing, alignment tool, and a pilot bearing where the car needs one. Input spline is 1 inch and the kit weighs about 27.4 lb.

Symptoms that point to the clutch

• Revs rise faster than road speed in third or fourth gear once boost comes in
• Slip that started after a tune, intake and exhaust, or a turbo upgrade
• Engagement point climbing higher in the pedal as the factory disc wears
• Judder pulling away on a hill or backing up a driveway
• Hot clutch smell after launches or a day at an autocross

How to confirm before you buy

Try a roll-on in fourth gear from about 2,500 rpm at full throttle. If the tach jumps without the car pulling harder, the clutch is slipping. Before buying a twin disc, rule out a weak slave or master cylinder, a pedal that does not return, and oil from the rear main seal on the bellhousing, because any of those will ruin a new clutch too. Our slipping diagnosis guide explains how to tell clutch slip from gearbox problems, and the manual versus automatic repair cost guide helps you budget the job.

Fitment

Our listing is cataloged for the 2013-2023 Subaru WRX with a manual transmission. ACT's application chart for T1SS-S01 is wider. It covers the 2006-2014 Impreza WRX and 2013-2014 WRX, the 2015-2026 WRX including the 2022-up 2.4 liter cars, and turbo Legacy GT, Outback XT, Forester XT and Baja Turbo models built between 2005 and 2012. Some single-disc WRX kits split at mid-2018 by VIN, but ACT lists this Mod-Twin across all 2018 and 2019 WRX trims. It is not listed for US-market STI models, which use different Mod-Twin part numbers. If your car has a swapped gearbox or engine, send the year and VIN before ordering. You can browse other options in our rebuild kits department.

Install notes

• Use the ACT flywheel supplied in the kit; the twin disc is built and balanced as a matched assembly.
• Assemble the friction plates, floater and hub in the order shown in ACT's instructions, then center them with the supplied tool before tightening the cover bolts evenly in a star pattern to spec.
• Install the new release bearing, and the pilot bearing if your car uses one. Check the clutch fork pivot and slave cylinder while the transmission is out.
• Bleed the clutch hydraulics with the brake fluid the car specifies until the pedal is firm and the clutch fully releases.
• Break in the organic friction plates for 300 to 500 miles of mild, stop-and-go driving before hard launches, as ACT recommends, and do not overheat the clutch during that period.
• Expect a 15 to 40 percent increase in pedal effort, which is typical of ACT's Heavy Duty plates.

If you plan to add more power later, the Mod-Twin 225 XT version (T2SS-S01) uses the stiffer Xtreme spring and is rated for 710 ft-lb.

Does T1SS-S01 fit the 2022 and newer WRX?

Yes. ACT's application chart lists it for the 2022-2026 WRX with the 2.4 liter engine as well as earlier WRX models. Our listing is cataloged for 2013-2023, so send your VIN if you want us to confirm.

Does it fit a WRX STI?

Not a US-market STI. ACT does not list T1SS-S01 for US STI models, which use separate Mod-Twin part numbers.

Is a flywheel included?

Yes. ACT includes a CNC-machined, balanced flywheel, along with the release bearing, alignment tool, Monoloc collar and a pilot bearing where needed.

What is the difference between T1SS-S01 and T2SS-S01?

Both are Mod-Twin 225 sprung street kits. T1SS-S01 uses the Heavy Duty diaphragm and is rated at 625 ft-lb. T2SS-S01 uses the Xtreme diaphragm, is rated at 710 ft-lb, and has a heavier pedal.

Can the Mod-Twin be rebuilt later?

Yes. ACT describes the Mod-Twin as fully rebuildable, and most components, including the sprung hub, can be ordered separately.

How long is the break-in?

ACT recommends 300 to 500 miles of mild stop-and-go driving on organic street friction before racing or hard launches.

• Transmission Slipping Diagnosis Guide
• Automatic vs. Manual Transmission Repair Cost: What to Actually Expect
• Rebuild vs Replace vs Reman Transmission