Installing a Clutch Masters FX400 in a 400 HP Subaru WRX is a meaningful upgrade for enthusiasts who have pushed their engine past the factory torque limits. The FX400 is a sprung-hub, six-puck ceramic-metallic clutch designed to handle up to 400 ft-lbs of torque, making it an ideal match for a Stage 2 or mild built WRX running a larger turbo, injectors, and an aggressive tune. While the factory clutch begins to slip around 300 hp, the FX400 provides a positive engagement, higher clamping force, and the durability to survive repeated hard launches and track days. However, the trade-off is a heavier pedal feel and a more abrupt engagement than a stock or organic disc. This guide covers each phase of the swap, from removing the old clutch to breaking in the new one, along with a realistic look at the total cost.

Tools and Materials Needed

Before starting, gather the following tools and replacement parts. Having everything on hand avoids frustrating trips to the auto parts store mid-job.

  • Clutch Masters FX400 clutch kit – includes pressure plate, disc, and release bearing (pilot bearing and alignment tool sold separately).
  • Flywheel – either resurface the existing single-mass flywheel or replace with a new one (e.g., OEM or aftermarket lightweight).
  • Socket set – ⅜” and ½” drive with metric sockets (10mm, 12mm, 14mm, 17mm, 19mm, 22mm).
  • Torque wrench – two preferred (⅜” for small bolts, ½” for flywheel and pressure plate).
  • Jack and four jack stands – the car must be level and high enough to slide a transmission under.
  • Transmission jack (or floor jack with a block of wood) – supports the trans during removal and installation.
  • Clutch alignment tool – often included with the kit, but verify; a plastic universal tool works fine.
  • Pilot bearing puller – needed to remove the original pilot bearing from the crankshaft.
  • Brake cleaner – to degrease flywheel and pressure plate surfaces.
  • Thread locker – medium-strength (blue) for pressure plate bolts, high-strength (red) for flywheel bolts if replacing.
  • Safety glasses, gloves, and antiseize compound.
  • Optional but helpful: transmission fluid (e.g., 3-4 quarts of Motul 300 or Subaru Extra-HP), new flywheel bolts (single-use), and a clutch alignment tool with stepped collet for the pilot bearing.

Preparation Steps

Proper preparation saves time and ensures safety. Work in a well-ventilated garage with concrete floor.

  • Disconnect the negative battery terminal to prevent accidental starter engagement.
  • Raise the vehicle and secure it on four jack stands at the frame rails – ensure the car is level.
  • Remove both front wheels for easier access to the transmission bellhousing.
  • Drain the transmission fluid (if planning to replace) – the drain plug is on the bottom of the transmission extension housing.
  • Remove the intercooler (top mount) to access the top transmission bolts – this prevents stripping them over the bellhousing.
  • Remove the starter motor (two 12mm bolts) and set it aside, leaving the electrical connector attached if possible.
  • Disconnect the clutch slave cylinder from the transmission bellhousing (two 12mm bolts) and zip-tie it out of the way – do not disconnect the hydraulic line.

Removing the Old Clutch

The removal process requires careful support of the transmission and attention to hidden bolts.

  • Remove the driveshaft – unbolt the four 12mm bolts at the rear differential flange, then slide the driveshaft out of the transmission and remove the carrier bearing bolts (17mm).
  • Remove the downpipe and exhaust system if needed; some Subaru models require dropping the downpipe to access the bellhousing brace.
  • Support the transmission with a jack or transmission jack. Use a block of wood between the jack and the trans to avoid damaging the oil pan.
  • Remove the transmission crossmember (two 14mm bolts and two 17mm nuts).
  • Remove the transmission-to-engine bolts – there are typically four 17mm bolts and one 14mm bolt at the top, plus a 12mm bolt for the ground strap. Use extensions and a swivel socket for the top bolts.
  • Carefully lower the transmission a few inches to access the clutch fork and release bearing if needed, then disconnect the clutch fork from the release bearing (often a clip or spring).
  • Slide the transmission rearward until the input shaft clears the clutch disc. Support the transmission and set it aside.
  • Remove the old pressure plate – loosen the bolts in a crisscross pattern to prevent warping.
  • Remove the old clutch disc and pilot bearing. Use the pilot bearing puller to extract the bearing from the crankshaft.
  • Remove the flywheel – if it has the original bolts, they may be single-use (check Subaru service manual). Use a flywheel holding tool or a large flathead screwdriver to lock the ring gear.
  • Clean the flywheel mounting surface and crankshaft flange with brake cleaner. Inspect the rear main seal; replace if leaking.

Installing the Clutch Masters FX400

Flywheel Installation

If you are reusing the original flywheel, have it resurfaced at a machine shop to eliminate glazing and warpage. New flywheel bolts are highly recommended. Apply a small amount of thread locker (red) to the bolt threads. Torque the flywheel bolts in a star pattern to 75–85 ft-lb (check your specific kit – Clutch Masters may specify a different value).

Pilot Bearing Installation

Install the new pilot bearing (usually included in the FX400 kit) into the crankshaft recess. Use a suitable driver (socket of the same diameter) and a hammer to seat it flush. Avoid driving it too deep.

Clutch Disc and Pressure Plate

Insert the clutch alignment tool through the clutch disc, then into the pilot bearing. This centers the disc. Place the pressure plate over the disc and align the dowel pins. Tighten the pressure plate bolts evenly in a crisscross pattern. Torque to 30–35 ft-lb (blue thread locker on bolts). Remove the alignment tool.

Transmission Reinstallation

Before lifting the transmission, apply a thin film of high-temperature grease to the input shaft splines and the pilot bearing bore. This prevents premature wear. Slide the transmission rearward onto the clutch disc – it may require wiggling. Never force the transmission with bolts; if it sticks, check spline alignment. Rotate the output shaft while pushing the transmission forward to help the splines engage. Once seated, install the transmission-to-engine bolts and torque to 45–55 ft-lb (17mm bolts). Reinstall the crossmember, starter, slave cylinder, driveshaft, and exhaust components. Fill the transmission with fresh fluid (about 3.5 quarts for the 5-speed; check dipstick for 6-speed).

Final Steps

  • Reconnect the battery and check all electrical connectors.
  • Bleed the clutch hydraulic system – open the bleeder on the slave cylinder, have an assistant press the pedal, close bleeder, repeat until no air bubbles appear. Use fresh DOT 4 brake fluid.
  • Adjust the clutch pedal free play – the FX400 typically requires a slight pedal adjustment to ensure full disengagement. Consult the Clutch Masters instructions for the spec (usually 0.5–1.0 inch of free play at the pedal pad).
  • Lower the vehicle, then start the engine. Listen for any unusual noises, especially from the clutch area. While stationary, press the clutch pedal and shift through all gears (engine off first, then with engine running).
  • Test drive gently on a quiet road – check for slippage, chatter, or difficulty engaging gears. The FX400 will have a more aggressive engagement; some chatter at low RPM is normal until the disc breaks in.

Break-In Procedure

Proper break-in is critical for long life. For the first 500 miles, avoid hard launches, sustained high-RPM driving, and slipping the clutch excessively. Use normal starts from a stop, allow the clutch to engage smoothly, and vary driving speeds. After break-in, perform 20–30 moderately aggressive launches (full throttle from 3,000–4,000 rpm) to fully seat the disc and pressure plate. The clutch will then be ready for full power.

Cost Considerations

The Clutch Masters FX400 clutch kit retails between $600 and $800 depending on the vendor and whether you purchase the kit with flywheel, bearing, and alignement tool. Here is a realistic budget breakdown:

  • Clutch Masters FX400 kit: $600–$800
  • Flywheel resurfacing or new replacement: $50–$150 (resurface) or $200–$400 (new OEM or lightweight).
  • New flywheel bolts: $15–$25
  • Pilot bearing and release bearing: usually included in kit, but budget $20 if not.
  • Transmission fluid (3–4 quarts): $40–$80
  • Brake fluid, thread locker, brake cleaner: $15–$30
  • Shop labor (if not DIY): $400–$700 (Subaru clutch jobs are labor-intensive, typically 5–8 hours).
  • Special tools (pilot bearing puller, transmission jack, torque wrench): $100–$200 if you need to buy them.

Total DIY cost ranges from $800 to $1,200 if you already own basic tools. Hiring a shop adds $1,200–$1,900 total. Hidden costs may include a new slave cylinder or clutch master cylinder if the original is weak, or unexpected repairs like a leaking rear main seal or worn shift fork. Inspect thoroughly while the transmission is out.

For additional guidance, consult the official Clutch Masters FX400 product page for exact torque specs and disc clearance. The IWSTI transmission forum has community-verified install threads. For service manual torque values, Subaru’s owner site provides base factory specs. A detailed walkthrough can be found on this video guide from Boosted Performance.

Conclusion

Installing a Clutch Masters FX400 on a 400 HP Subaru WRX transforms the car’s ability to deliver power reliably. The clutch is not a daily-driver-friendly unit – expect a stiff pedal and a binary engagement – but for anyone who tracks the car or regularly launches from a stop, it is a proven upgrade. Follow the steps methodically, respect torque specs and break-in, and the FX400 will provide thousands of miles of high-use service. Keep realistic cost expectations, and if you lack the tools or experience, pay a qualified Subaru specialist to do the job. The result is a drivetrain that can handle everything your built engine can throw at it.