XClutch 15-21 Subaru WRX STi Base 2.5L 10.5in Twin Sprung Organic Clutch Kit

Most 2015-2021 WRX STI owners shopping for a twin-disc clutch got here the same way: a bigger turbo or an aggressive tune on the EJ257, and a factory clutch that now slips in fourth and fifth the moment boost comes in. The XClutch XKSU23531-2A is a 10.5in twin-disc kit with sprung organic discs for the VA-chassis STI with the six-speed manual. It is meant to hold far more torque than the stock single disc while still letting you creep through a drive-thru without bucking.

What a twin-disc clutch kit changes in an STI

The STI sends the EJ257's torque through a six-speed manual and a driver-controlled center differential to all four wheels. With that much grip, the clutch has nowhere to slip off load except inside itself, which is why a modified STI tends to burn through a stock clutch rather than spin tires. A twin-disc layout stacks two friction discs with a floating intermediate plate between them, so the same pressure plate clamps four friction faces instead of two.

XClutch lists this kit as heavy duty, diaphragm type, twin disc, sprung organic, recommended for high power street use. In XClutch's stage system the -2A suffix is Stage 4, the organic multi-disc group made for very high powered street cars. Organic facings engage progressively and are kind to the flywheel. The sprung hubs absorb engagement shock before it reaches the input shaft, which is a real consideration on a gearbox that also feeds a center differential and two axles.

Symptoms that point to the clutch

• Revs climb with no added speed in the upper gears at full boost
• Slip that started after a tune, turbo or boost increase
• Shudder pulling away, worst when the car is hot
• A squeal or chirp that changes when the pedal is pressed, pointing at the release or pilot bearing
• Notchy engagement into gears with the pedal fully down

There is no specific trouble code for a slipping clutch. A boost or fueling fault can feel like slip, so clear any engine codes before blaming the clutch.

How to confirm it before you buy

Do a high-gear pull from low rpm and watch the tachometer against road speed; a clutch that holds will not let the needle run ahead. Check that the clutch fluid is clean and full and that the pedal returns fully, because a dragging release or a sticky hydraulic system can feel like a worn disc. If the gearbox has to come out anyway, weigh the labor against the parts with our manual versus automatic repair cost guide.

Fitment

This listing covers the 2015-2021 Subaru WRX STI 2.5L six-speed, including Base and Limited. XClutch's application data for this part number also includes the 2015 Launch Edition, the 2016 Series.HyperBlue, the 2018 Type RA and the 2019 S209, plus the earlier 2004-2014 Impreza WRX STI and the 2007-2009 Legacy GT spec.B with the six-speed. It does not fit the non-STI WRX, which uses a different gearbox. If your car has had a transmission swap, or you are not sure which unit is in it, send us the year and VIN before ordering. If you want a single-disc setup instead, the XClutch Stage 1 sprung organic STI kit is the street-friendly option, and the 9in twin sprung ceramic version trades some street manners for track heat capacity.

Install notes

• XClutch lists the friction discs, pressure plate, release bearing, flywheel, pilot bearing and an aligning tool for this kit. Check everything against the packing list before the old clutch comes out.
• Fit the new pilot and release bearings; they are cheap next to the labor of pulling the six-speed again.
• Clean the crank flange, keep oil and grease off the friction faces and use a thin coat of high-temperature grease on the input spline only.
• Align both discs before tightening the pressure plate, then torque the bolts evenly in a cross pattern. Our 18-piece clutch alignment tool kit is a good backup.
• Bleed the clutch hydraulics with fresh DOT 3 or better fluid; XClutch suggests DOT 4 or 5.1 for performance driving.
• Bed in gently for the first 1,000 km, about 620 miles, using low-rpm engagements and no launches.

A twin-disc STI will be a little noisier at idle than stock. XClutch's 10.5in twin kits use a strap-driven intermediate plate in some applications to cut pedal-down rattle, but some extra driveline noise is normal with any twin-plate clutch.

Will this kit fit a 2015-2021 WRX that is not an STI?

No. This kit is for the STI six-speed. The regular WRX uses a different transmission and clutch, so it needs a different kit.

Does the kit come with a flywheel?

XClutch lists a flywheel along with the twin discs, pressure plate, release bearing, pilot bearing and alignment tool for XKSU23531-2A. Confirm the contents on arrival before you start the job.

How much power can it handle?

XClutch places it in Stage 4, its organic multi-disc range recommended for very high powered street cars. If your build is aimed at dedicated track use, a ceramic or motorsport-series kit is the better match.

Will the clutch pedal be heavier than stock?

It can change. XClutch says a performance clutch can raise or lower pedal effort and will usually change where and how the clutch engages, so expect a short adjustment period.

How do I break in the new clutch?

Drive gently for the first 1,000 km, about 620 miles. Use low-rpm engagements, avoid launches and avoid slipping the clutch while the facings bed into the flywheel.

• Automatic vs. Manual Transmission Repair Cost: What to Actually Expect