Wilwood Thermlock FSL4R-ST Caliper, Left / 1.88/1.62-Inch Bores / 1.25-inch Rotor Width

This left-hand four-piston Superlite 4R/ST has a 1.88/1.62-inch bore combination and Thermlock insulating pistons. Internal fluid transfer and radial attachment are incorporated into its Type III anodized forged housing. Wilwood Engineering is a Camarillo, California-based designer and manufacturer of disc brake systems, founded by Bill Wood in 1977. Calipers, brake rotors, master cylinders, valves, fittings and brake lines form its range for motorsport, street-performance and specialized applications.

Technical Details

• Manufacturer part number: 120-13266. Component: Forged Superlite 4 Radial Mount caliper.
• Supply: one brake caliper, not a complete axle brake kit. Match the mating rotor, pads, bracket and connection hardware to the installation.
• The rotor channel is specified for 1.25-inch nominal width. Rotor outside diameter: 11.75 to 14.00 inches. Specified rotor-width limits: 1.15–1.35 inch.
• 5.98-inch radial mounting pattern, left hand; mounting height 1.63 inches and hole size 0.39 inch.
• Hydraulic inlet thread: 1/8-27 NPT. Use a fitting with the correct thread and sealing seat.
• Caliper weight: approximately 5.5 lb.
• 4 Thermlock pistons with 1.88/1.62-inch bore groups. The specified effective area is 4.84 sq in.
• Type III anodize finish on a forged aluminum caliper body.
• Piston dust boots: not fitted.
• Brake pad profile 7420; select friction material for the actual operating conditions.

Fitment & Compatibility

Choose the left orientation from the required installation geometry and rotor direction. Confirm the 1.15–1.35-inch rotor-width range, bracket offset and correct 7420 pad outline rather than assuming interchange with a different Superlite bore or body width.

PMB Performance has worked with brake components for over 20 years. Share the required piston sizing, rotor measurements and bracket drawing for help checking the match.