11.72" Front Vented Disc Brake, 73mm Caliper & Wheel Bearings

Mounted on the front steering spindle via inner and outer greased tapered roller wheel bearings is the one-piece cast-iron 11.72-inch vented brake rotor and 5×5.5" hub, straddled by a single-piston sliding iron caliper with a 73 mm (2.87-inch) phenolic piston, semi-metallic inboard and outboard brake pads, anti-rattle abutment clips, and a stamped dust splash shield.

How a Single-Piston Sliding Caliper Squeezes Both Sides of the Rotor: Hydraulic pressure pushes the 73 mm piston outward against the inboard brake pad. Once the inboard pad touches the rotor face, Newton’s third law (equal and opposite reaction) pushes the entire cast-iron caliper housing inward along two rubber-bushed slide pins—pulling the outer caliper fingers tightly against the outboard pad with identical clamping force.

How the Square-Cut Rubber Seal Retracts the Piston Automatically: There is no return spring inside a disc brake caliper! Instead, the square-profile EPDM hydraulic seal sits in a machined groove in the caliper bore. As the piston moves outward, friction stretches the rubber seal slightly forward; when you take your foot off the brake pedal, the rubber seal elastically snaps back to square—pulling the piston back by ~0.15 mm so the pads don’t drag.