Specifications
Part Details:
The Clutch Masters Billet Aluminum Master Cylinder is a complete clutch hydraulic upgrade for the 2015–2021 Subaru WRX and STI. It replaces the factory master cylinder with a 6061 billet aluminum unit featuring a 0.700″ bore, and eliminates the OEM clutch delay valve that is built into the factory unit.
The delay valve is a one-way regulating valve in the factory master cylinder that slows fluid returning from the slave cylinder after the clutch pedal is released. This delay is most noticeable during quick 1-2 gear shifts where the clutch needs to re-engage before the delay valve has finished cycling. Removing it allows the clutch to engage immediately upon pedal release, improving shift speed and pedal responsiveness.
This is a complete plug and play kit that includes everything required for installation and works with the OEM slave cylinder. The red anodized billet aluminum finish gives it a clean appearance under the hood. On the 2015 and up WRX and STI, the clutch master cylinder shares a reservoir with the brake master cylinder — a rubber hose is included to make this connection.
Important Note: This kit is designed for USDM left-hand drive vehicles only. It is not compatible with right-hand drive cars. Due to the wide range of adjustability on this master cylinder, it is highly recommended to verify the overall throw of the setup after installation to ensure the clutch diaphragm is not being overextended. A clutch pedal stop may be required depending on installation setup.
Key Features
- Fits 2015–2021 Subaru WRX and WRX STI (USDM LHD only)
- 6061 billet aluminum master cylinder with 0.700″ bore
- Red anodized finish
- Eliminates OEM clutch delay valve for immediate clutch engagement
- Adjustable push rod and clevis for precise pedal feel tuning
- Compatible with OEM slave cylinder
- Complete plug and play kit — everything included
What’s Included
- 6061 billet aluminum master cylinder (0.700″ bore)
- 3AN stainless steel line
- Billet aluminum master cylinder adapter and jam nut
- Barb fitting
- Rubber hose to connect factory reservoir to master cylinder
- Extended and adjustable push rod and billet clevis
- 2 banjo fittings with crush washers
- Jam nut tool
Frequently Asked Questions (FAQ)
What does eliminating the delay valve actually do?
The OEM delay valve slows clutch re-engagement after you release the pedal. Removing it means the clutch engages immediately when you let off, which makes quick 1-2 gear shifts noticeably faster and more precise.
Will this work with my stock slave cylinder?
Yes. This kit is fully compatible with the OEM slave cylinder.
Does this fit right-hand drive WRX or STI models?
No. This kit is designed specifically for USDM left-hand drive vehicles only.
Do I need to modify the brake fluid reservoir?
No. The kit includes a rubber hose that connects the existing shared reservoir to the new master cylinder. No modification to the reservoir is needed.
Is professional installation recommended?
Yes. Installation involves adjusting pedal geometry and push rod length and a full system bleed is required. Professional installation is strongly recommended to ensure correct setup and avoid overthrowing the clutch diaphragm.
Recommended Supporting Drivetrain Components
- Clutch Kits – pair this master cylinder upgrade with a performance clutch kit for a complete hydraulic system overhaul.
- Flywheels – commonly replaced alongside clutch kits for proper engagement and compatibility.
- Drivetrain Components – explore additional upgrades designed to support reliable power transfer.
Shipping
Shipping Options:
WrenchMastersAuto.com ships your performance parts safely, quickly and conveniently nationwide via the most trusted shipping carriers such as: UPS, Fed Ex, USPS, and DHL.
Delivery Times:
- In Stock: 3-7 Business Days
- Custom Orders: 2-6 Weeks, Please Email: [email protected] or Call: 727-565-9808 for Questions.
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