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Brake calipers are essential to helping your vehicle stop safely. Brake calipers are hydraulic actuators that transfer force from application of the brake pedal to the friction material(brake pads) via hydraulic fluid contained in lines that interconnect the brake pedal assembly and the calipers. Calipers may be used on the front or rear brakes and are mounted to the spindle assembly over the brake rotors.
What is it?
Calipers hold the brake pads.
There are two main types of calipers: floating calipers that move in and out relative to the rotor and have one or two pistons only on the inboard side of the rotor and fixed calipers that don't move but have pistons arranged on opposing sides of the rotor.
How Does it Work?
The transfer of energy begins with operation of the brake pedal, which transfers motion to the brake master cylinder.
Pedal motion causes a piston in the master cylinder to push hydraulic fluid out into the brake lines. The pressurized fluid is directed to the calipers and/or wheel cylinders at all four road wheels.
Pressurized brake fluid enters the caliper, filling the chamber behind the caliper piston and forcing the piston outward.
As pressurized brake fluid forces the caliper piston outward, it pushes the friction material into contact with the brake rotor.
The brake caliper applies braking pressure to the friction material proportionate to the applied force from the vehicle operator.
Upon completion of the braking action, the brake pedal is released, brake fluid pressure reduces and the caliper piston and friction material are retracted away from the brake disk.
How is it Made?
The caliper is traditionally cast of a lightweight aluminum material. Older brake caliper designs may be cast iron.
FA brake caliper can operate using 1, 2, 4 or even 6 pistons. Single piston designs are designed to allow the caliper to center during application so that the inboard friction material has an equally applied force with that of the piston side. Dual, 4 or 6 piston calipers apply hydraulic force from both sides of the caliper.
Many calipers float (center) on the rotor via caliper guide pins, components that affix the caliper to the caliper bracket assembly.
Calipers incorporate an integral "bleeder" screw, wherein any entrapped air can be removed, should the caliper or related hoses be removed or replaced.
Why Does it Fail?
Brake calipers most often fail when internal rust and corrosion cause the hydraulic piston to seize in the bore. This occurrence is easily avoided by periodically replacing your brake fluid.
Seized caliper guide pins are another frequent cause of caliper failure. If these pins seize in the caliper bracket bore, the bracket normally needs to be replaced. Use of a quality caliper grease can help to avoid this issue.
Broken bleeder screws are another frequent cause of caliper failure. These small hollow screws will sometimes bind in the caliper housing and break off when attempting to bleed air from the system.
What are the Symptoms of Failure?
Asymmetric brake pad wear, where either the inner or outer pad is worn more than the other usually indicates binding caliper guide pins.
Dissimilar pad wear on either the passenger or driver side often indicates that the side with less wear either has air trapped in that side of the brake hydraulics or the affected caliper has a seized piston. Steering pull under braking often accompanies this visual symptom.
Brake pads soaked with dark colored fluid and an accompanying odor often indicates a leakin
g brake caliper, where fluid has contaminated the friction material. A leaking caliper is unsafe and should be replaced at once.
What are the Implications of Failure?
Brakes are considered to be a critical safety system of any vehicle. A leaking, seized or binding brake caliper will reduce braking effectiveness and increase stopping distance. Any brake caliper that is suspect should be replaced.