Disc Brake System: Description and Operation

Fig 1 Disc Brake Assembly (Rear View):

The single piston sliding caliper disc brake assembly, consists of the one piece hub and disc assembly, the caliper, shoes and linings, splash shield and adaptor.
- The caliper is a one piece casting with the inboard side containing the single piston cylinder bore. A phenolic piston is used.

Fig 2 Disc Brake Assembly (Front View):

Disc Rotor
The cast iron braking disc has cooling fins or louvres that are cast integrally between the two machined braking surfaces (fig 2).

When the vehicle is in motion, the rotation of the disc cooling fins supplies air circulation between the braking surfaces for efficient cooling of the disc and prolonged lining life.

Fig 3 Cutaway View Of Disc Brake Assembly:

Splash Shield
The braking disc is protected from road splash (inboard side) by a shield bolted to the steering knuckle and by the wheel and tire on the outboard side.

Abutments
Two machined abutments on the adaptor position and align the caliper.

Retaining Clips
The retaining clips retain the caliper in the machined guides or "ways" on the adaptor and allow lateral movement of the caliper.

Flanges
Flanges on the outboard shoe are used to radially locate and position the shoe on the caliper fingers.

Fig 6 Removing Outboard Shoe:

OPERATION
The inboard shoe is held in a captive position by the adaptor. All braking force on the outboard shoe is taken by the caliper. The inboard shoe reacts directly on the adaptor.

The square cut rubber piston seal is located in a machined groove in the cylinder bore and provides a hydraulic seal between the piston and the cylinder wall. The adaptor is mounted on the steering knuckle by two special nylock bolts.

Dust Boot
A moulded rubber dust boot installed in a groove in the cylinder bore and piston keeps contamination from the cylinder wall and piston. The boot has a wiping lip that prevents contamination in the bore area.

As the brake pedal is depressed, hydraulic pressure is applied against the piston. This force is transmitted to the inboard brake shoe and lining and the inboard braking surface of the disc. As force increases against the disc from the inner lining, the caliper assembly moves inboard, sliding on the machined adaptor "ways", thus providing a clamping force on the disc.

Fig. 2 Piston Seal Function:

When the brake pressure is released, the piston seal (distorted by applied pressure) returns to its normal position, pulling the piston back to released position, creating a slight running clearance between outer shoe and the disc.

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