Disc Brakes
The front calipers are a dual piston type and rear calipers are a single piston type. The calipers are free to slide laterally, this allows continuous compensation for lining wear. When the brakes are applied, fluid pressure is exerted against the caliper piston. The fluid pressure is exerted equally and in all directions. This means pressure exerted against the caliper piston and within the caliper bore will be equal. See Fig 1. Fluid pressure applied to the piston is transmitted directly to the inboard brake shoe. This forces the shoe lining against the inner surface of the disc brake rotor. In other words, fluid pressure acting simultaneously on both piston and caliper, produces a strong clamping action. When sufficient force is applied, friction will attempt to stop the rotors from turning and bring the vehicle to a stop. Applying and releasing the brake pedal generates only a slight movement of the caliper and piston. Once the pedal has been released, the caliper and the piston return to a rest position. The brake shoes do not move an appreciable distance from the rotor. In fact, the clearance between the shoe and rotor is usually at or close to zero. This is to keep road debris from getting between the rotor and lining and to wipe the rotor surface clear each revolution. The caliper piston seal controls the amount of piston extension needed to compensate for normal lining wear. During brake application, the seal is deflected outward by fluid pressure and piston movement. See Fig 2. When the brakes are released, the seal relaxes and retracts the piston. The amount of piston retraction is determined by the amount of seal deflection. Generally the amount is just enough to maintain contact between the piston and inboard brake shoe.