Disc Brake System: Description and Operation

Fig 1 Disc Brake Assembly (Rear View):

Brake Assembly
The brake assembly includes a single piston sliding caliper, caliper to steering knuckle adaptor, ventilated rotor and a splash shield.
- The splash shield -- bolted to the adaptor -- protects the bearings and inboard surface of the rotor from road splash.
- The wheel protects the outboard surface of the rotor and brake assembly.

Fig 2 Adaptor/Steering Knuckle Attachment:

The caliper attaches to and slides on machined ways within the adaptor -- attached to the steering knuckle.

Fig 8 Removing Or Installing Inboard Shoe:

Shoes and Linings
The inner shoe and lining is installed with the ends of the shoe in the adaptor.
- An anti-rattle spring is positioned between the leading edge of the shoe and the adaptor at the bottom of the caliper.

Fig 7 Removing Outboard Shoe From Caliper:

The outer shoe and lining is installed with the shoe flanges bearing against the shoe locating and torque abutment surfaces on the caliper.

The linings are riveted to the shoes, and the inner and outer shoes are not interchangeable.

Fig 3 Caliper Assembly:

Caliper Housing
The caliper housing -- single piece casting -- is positioned on the adaptor against machined surfaces at the trailing end.
- A caliper support key is installed between the leading edge of the caliper and the adaptor with a support spring inserted between the key and the caliper.
- A key retaining screw keeps the key from sliding out of the anchor bracket.
- A single hydraulic piston is inserted into the cylinder bore in the caliper housing with the hydraulic fluid inlet coming into the bottom of the bore.
- A square section seal is fitted into an annular groove in the cylinder bore, and a rubber boot is used to seal the piston and caliper bore from road splash and contamination.
- A bleeder screw is located above the cylinder bore to bleed air from the system.

Operation
When the brake pedal is depressed, brake fluid from the master cylinder is displaced into the caliper cylinder. This moves the piston outward and forces the inner shoe and lining assembly against the in- board surface of the rotor.

The reaction of the inner lining pressing against the rotor moves the caliper housing slightly inboard. The outer legs of the caliper housing force the outer shoe and lining assembly against the outboard surface of the rotor.

The two shoe and lining assemblies clamp the rotor in a vise-type movement to provide the braking action. The braking torque is transferred from the linings to the shoes. The torque from the inner shoe is transferred directly to the anchor bracket, while the torque from the outer shoe is transferred through the caliper to the anchor bracket.

Fig. 2 Piston Seal Function:

When the brake pedal is released, the piston seal (distorted by applied pressure) retracts the piston into the cylinder, leaving the caliper housing free to slide slightly outboard, thus releasing the brakes.

Automatic Adjustment
Automatic adjustment is obtained by outward relocation of the piston as the inboard lining wears and inward movement of the caliper as the outboard lining wears, thus maintaining correct adjustment at all times.