11.03 × 2.25" Duo-Servo Rear Drum Brake & Parking Brake

Bolted to the outer flanges of the Ford 8.8 rear axle tubes are the 11.03 × 2.25-inch duo-servo rear drum brakes. Inside each finned cast-iron brake drum sit the stamped backing plate, top anchor pin, dual-piston hydraulic wheel cylinder, primary (front) and secondary (rear) lined brake shoes, lower floating star-wheel screw adjuster, automatic adjuster cable and lever, hold-down springs, and the mechanical parking-brake lever and strut.

Duo-Servo Self-Energizing Physics: Unlike disc brakes, a duo-servo drum brake uses the forward rotation of the truck to multiply its own braking force! When the top wheel cylinder pushes both shoes outward against the spinning drum, friction drags the front (primary) shoe downward in the direction of rotation. Because the bottom of both shoes are connected by a floating star-wheel link (not anchored to the backing plate), the rotational drag of the primary shoe jams the bottom of the rear (secondary) shoe upward into the top anchor pin—creating massive wedging amplification.

Automatic Star-Wheel Self-Adjustment: Every time you back the truck up and step on the brakes, the secondary shoe pulls slightly away from the top anchor pin, tugging a thin steel cable that lifts a pivoted lever. When you release the brake, the spring pulls the lever down—clicking the toothed star-wheel screw one notch wider if lining wear has created enough slack.