Wilwood 120-12603 FNSL4R-ST Forged Billet Rear Brake Caliper

The Wilwood FNSL4R-ST forged billet brake caliper delivers championship-proven performance for high-performance braking applications. Designed as a rear caliper to provide matched braking bias when paired with larger front calipers like the Aero6/ST, this four-piston caliper combines advanced engineering with race-tested durability.

Advanced Forged Construction:

Each caliper body is stress-flow forged from premium grade aluminum alloy billets using computer-generated solid modeling and FEA stress analysis. This forging process re-aligns the metal's internal grain structure to flow within the contour of the caliper body, eliminating stresses and interruptions that occur in traditional billet machining. The result is an exceptionally strong, lightweight caliper weighing just 4.9 pounds.

Thermlock® Piston Technology:

Equipped with Wilwood's exclusive Thermlock® pistons, this multi-part piston design creates a highly efficient thermal barrier that significantly reduces heat transfer from the pads to the caliper body, seals, and brake fluid. This thermal management translates to longer component service life and reduced risk of heat-induced pedal fade during demanding driving conditions.

Key Features:

• Four-piston forged billet aluminum construction with stress-flow forging
• Thermlock® pistons for superior heat management
• SRS (Sliding Re-Traction System) bridge plates eliminate pad wear on caliper bridges and prevent pad rattle
• Two-piece bleed screws on each end for easy bleeding and track debris protection
• Internal fluid crossovers prevent damage from external hazards
• High-temperature square-faced bore seals provide maximum sealing area and controlled piston retraction
• Compatible with full range of Wilwood pad compounds for various applications
• Anodized finish for corrosion resistance and durability

The SRS bridge plates not only extend caliper service life by eliminating bridge wear from pad gouging, but their spring-loaded action also dampens harmonic vibrations that contribute to brake squeal. Ideal for competition, track day, and high-performance street applications requiring precise rear brake bias control.