What does the brake caliper do?

A brake caliper is a vital part of the disc brake system of a vehicle. A disc brake, as illustrated below, is a type of brake that uses a brake caliper to squeeze pairs of pads against a disc-shaped rotor to create friction to decelerate or stop the vehicle.

brake caliper

Specifically, inside each caliper is a pair of metal plates bonded with friction material, known as brake pads. The outboard brake pads are on the outside of the rotors (toward the curb) and the inboard brake pads on the inside (toward the vehicle). When the brake is stepped, brake fluid from the master cylinder generates hydraulic pressure on one or more pistons in the brake caliper that forces the pads against the rotor. The brake pads have high-friction surfaces and are used to slow the rotor down or even bring it to a complete stop. When the rotor slows or stops, so does the wheel as they are attached to each other.

How Many Types of Brake Calipers Are There?

Brake calipers can be variously categorized according to their structure and power source.
When it comes to the structure of brake calipers, they can be divided into two types, floating and fixed. A fixed brake caliper does not move relative to the disc and is hence more vulnerable to disc imperfections. It adopts one or more pairs of opposing pistons to clamp from each side of the disc, and is more sophisticated and costly than a floating brake caliper.
Fixed and floating calipers compared

Floating Brake Caliper

A floating brake caliper moves with respect to the disc, along a line parallel to the axis of rotation of the disc; a piston on one side of the disc pushes the inner brake pad until it makes contact with the braking surface, then pulls the caliper body with the outer brake pad so pressure is applied to both sides of the disc. However, floating caliper designs with a single piston are vulnerable to sticking failure because of dirt or corrosion entering at least one mounting mechanism and stopping its normal movement. This can lead to the brake caliper’s pads rubbing on the disc when the brake is not engaged or engaged at an angle. Sticking can be a result of infrequent vehicle use, failure of a seal or rubber protection boot allowing debris entry, dry-out of the grease in the mounting mechanism and subsequent moisture incursion leading to corrosion, or any combination of these factors. Consequences can include reduced fuel efficiency, excessive heating of the disc or excessive wear on the affected pad. A sticking front caliper may also cause steering vibration.

Swinging brake caliper

Another type of floating caliper is a swinging brake caliper. Unlike a pair of horizontal bolts that enable the caliper to move straight in and out respective to the car body, a swinging brake caliper uses a single, vertical pivot bolt located somewhere behind the axle centerline. When the driver presses the brakes, the brake piston pushes on the inboard piston and rotates the whole caliper inward, when viewed from the top. Because the angle of the swinging caliper’s piston changes relative to the disc, this design uses wedge-shaped pads narrower in the rear on the outside and narrower on the front on the inside.

When it comes to power source that pushes the piston, brake calipers fall into hydraulic type and pneumatic type. The former uses brake fluid to push the pistons while the latter works with air pressure. Pneumatic brake calipers are more widely used when the requirements for power and pressures are not that demanding, whereas hydraulic brake calipers are used where greater amounts of power and pressure are required. Both of these two types have their own distinct advantages, some of which have been detailed in the following chart.

Condition Pneumatic Hydraulic
Life Up to 10 years Up to 15 years
Initial cost, brake Approx. 50% hydraulic brake cost High
Energy cost Medium Higher
Maintenance Low cost repairs Expensive replacement costs
Noise Quiet – compressor normally remote Loud — power unit nearby
Temperature limit Above freezing Sub-zero
Wet conditions Seal protection to IP67 Underwater compatible
Clamp force 2,550 lb 3,143 lb
Broken hoses Clean; hose whip is dangerous Dirty, messy
Controls cost Lower, less complicated Higher, more components
Pressure, maximum 80 to 100 psi 1,000 to 5,000 psi
Release pressure 72 psi 250 psi
Friction-facing area 15.70 sq. in. 30.96 sq. in.
Facing life 628 hp-hours 1,238 hp-hours
Safety Non-sparking Flammable
Actuation method Air or nitrogen are compressible Oil not compressible
Control system Open, exhausts air to atmosphere Closed, recirculates oil
System flexibility Easy to modify and change Not easy to expand
Disc diameter 18 in. 14 in.
Disc thickness 0.50 in. 1.0 in.
Disc inertia 10 lb-ft2 7 lb-ft

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