The Wilwood 120-13839-RD is the red powder-coated version of the Forged Billet Dynalite Internal, which the manufacturer describes as the next generation enhancement of the venerable Forged Dynalite series calipers. It is a four-piston, forged aluminum, lug-mount caliper with 1.38 inch pistons and stainless steel pistons, sized for a 0.81 inch rotor.
The case for paying more than for a basic caliper rests on rigidity and fluid handling. Wilwood's spacer-less, single split bridge design is intended to make this the stiffest and most visual pleasing caliper in the Forged Dynalite line. The manufacturer ties reduced deflection and smaller fluid volume displacement to firmer pedal feel and less pedal travel. Internal fluid passages remove external crossover lines, and high-temperature seals and stainless steel pistons are standard. Fitment is a direct replacement for Dynalite and similar calipers with 5.25 inch centered mounting tabs, and pad options include the 7112 type brake pad with PolyMatrix and SmartPad compounds for track and street heat ranges.
The manufacturer lists a 0.81 inch rotor width, a 13.06 inch rotor diameter, and a 5.25 inch lug mount center. Confirm your bracket and rotor match these figures before ordering.
No. According to the manufacturer, internal fluid passages eliminate the need for external tubes.
Per the manufacturer, the four corner bleed screws allow one caliper to be mounted in any front, rear, right or left position.
The manufacturer's install guidance calls for Wilwood Hi-Temp 570 grade fluid or higher, and recommends its EXP 600 Plus racing fluid for severe braking or sustained high-heat use.
For most DIY builders this is a pad swap, mounting, and full bleed rather than a major fabrication job. Because the caliper uses internal crossover, there are no external lines to route, but four corner bleed screws assure simple and effective air evacuation from the system. Owners on user forums note that the newer billet versions have the internal crossover, and that the lower bleeders can stay in place or be replaced with plugs. The manufacturer's bleed sequence is to begin with the caliper farthest from the master cylinder, bleeding the outboard screw first, then the inboard. Keep brake fluid off pad and rotor faces, and use a catch bottle with a hose during bleeding, as the manufacturer advises. Expect the pistons to be stiff when reseating new pads; owners on user forums have needed a C-clamp or a pad-backed tool to push them back.
