The Wilwood Forged Superlite Internal 4 Piston ST Calipers provide the pad wear performance advantages of differential bore pistons with the option for ultimate heat protection using Thermlock pistons in the ST models. Differential piston bores compensate for leading-edge mechanical loading and temperature variances across the pad face to reduce pad taper wear in sustained high-temperature applications. Thermlock pistons block heat transfer from the pads and reduce temperatures in the caliper, fluid, and seals by up to 25% over standard stainless steel pistons. These are the go-to calipers for all types sustained hard braking on dirt and asphalt ovals and a wide range of off-road, rally and road course applications.
The new FSLI4/ST models use the latest innovation to the Superlite family of calipers. They have been redesigned with internal fluid ports that eliminate the external fluid cross-over tubes, along with any potential problems that could arise from a damaged tube. The transfer tube has been replaced with two additional bleed screw assemblies which allow this group of right and left hand oriented differential piston bore calipers to be mounted in either a leading or trailing position.
The most noteworthy feature of all the FSLI caliper models is the exceptional strength and reduced weight of the forging. With assembled weights just at 4.4 pounds, the caliper body design in itself is a product of computer generated solid modeling and stress analysis technology. Each caliper features closed end bridges with a radial transition down to the main body and piston bore housings. The elimination of machined steps and sharp shoulders in this critical area provides a measurable increase in overall body strength and resistance to deflection under load. Every FSL body is stress-flow forged from a premium grade aluminum alloy billet. Stress-flow forging realigns the metal's internal grain structure to flow within the contour of the caliper body. This process eliminates the stresses and interruptions to the internal grain structure that occur when machining a straight block billet.
FSLI calipers use high strength steel main bridge bolts in tension and a supplemental center bridge bolt to provide maximum resistance and strength against deflection and body separation under load. The center bridge support also provides positive pad retention with quick access when it’s time for service. Clamping force, structural deflection, and volume displacement tests have proven the superior strength and efficiency of the FSL. Simply stated, there is no better way to build a stronger or more efficient one or two-piece aluminum caliper body at equal or lower weight.
FSLI calipers feature all of Wilwood’s latest refinements and proven performance features including replaceable SRS stainless steel bridge plates. SRS plates extend caliper life by preventing wear at the bridge abutments otherwise caused by pad edge gouging. Spring tension in the SRS plates also eliminates pad rattle and helps to dampen the vibration harmonics that can contribute to squeal under braking. Other standard Wilwood features include high-temperature, square-faced o-ring seals for positive sealing, controlled piston retraction, and long service life in high heat conditions. Machined stainless steel pistons are used in the standard models to resist corrosion, retard heat transfer, and eliminate backside deflection under pressure. Two-piece bleed screw assemblies provide long, reliable service life and are easily replaced if necessary.