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How a brake caliper works and what happens when calipers go bad

A brake caliper in situ on a car

Your car or bike's brake caliper is one of its most critical components. Without a working caliper, it's simply not safe enough to use until it's been fixed or replaced. Here we explain how brake calipers function, how they differ in design and how to tell if there's a problem with your caliper.

How does a brake caliper work?

Your car wheels are attached to circular metal rotors and these rotors spin along with the wheels.

The caliper fits over the spinning rotor and works much like a clamp – step on the brake pedal or pull the brake lever and the pads within the caliper are pushed out via pistons to make contact with the spinning rotor. The friction generated by the action of the pads on the disc is is what slows the vehicle.

There are several types of calipers:

Floating calipers

What about a floating caliper?

A floating brake caliper has piston(s) on only one side of the disc but contains pads which make contact with both sides. The caliper slides back and forth on bushings or pins, acting as a clamp.

When the brakes are applied, the piston pushes the brake pad only on the inboard side of the disc.

The caliper then slides on the bushings or pins and squeezes the outboard pad against the rotor, initiating braking action.

Sliding caliper

How does a sliding brake caliper differ from a floating caliper?

The sliding caliper type is mounted in a slot in the caliper adapter. It is a variation of the floating caliper design, using a single piston and operating on the same principle – the piston applies pressure to one brake pad and the movable caliper applies pressure to the other.

What about fixed calipers?

A fixed caliper usually consists of two, four, six or even eight pistons. A fixed caliper is mounted to a bracket with no sliding pins or bushings in its mount.

The fixed caliper consists of an equal number of pistons on both the inboard and outboard halves of the caliper. It is generally accepted that fixed calipers have better performance, but at a higher cost. Fixed calipers with multiple pistons tend to be installed on high-performance cars.

What can go wrong with a brake caliper?

A brake caliper has moving parts that can go wrong from time to time.

When brakes seize it can be because the piston becomes stuck within the caliper, the pads become stuck to the disc, or on single-piston calipers the slide pins can seize.

If the brakes seize when the vehicle has been unused then the symptoms are fairly obvious: you can't get the car to move. Find out how to unseize a brake caliper here.

How can I boost my car’s braking potential?

Short of removing and replacing your car’s braking system with larger rotors, you can fine-tune your present braking system to perform better:

  • Bigger brake caliper pistons: Larger pistons have greater clamping area and thus more clamping force over the rotor
  • More pistons: High-performance calipers that allow for more pistons - six-piston and even 12-piston models can increase the clamping force of the caliper.
  • Less heat retention: Brake air scoops can help in this area; larger rotors can spread excess heat over a larger area
  • Differential bore calipers It helps if the pistons closer to the rear edge of the caliper are larger. Differential-bore calipers use smaller pistons up front, larger pistons toward the back.
  • Porsche Composite Ceramic Brakes (PCCB): These are among the best brakes you'll find in any road car. They're made from siliconised carbonfibre, with very high temperature capability, a 50% weight reduction over iron discs, a significant reduction in dust, and enhanced durability in corrosive environments over conventional iron discs. The discs are internally vented, similar to cast-iron ones, and cross-drilled. The cost, as you can imagine, is exorbitant.
Brake caliper tool

Brake caliper tool

A specialised (but relatively cheap piece of kit) is the Brake Caliper Tool. When a pad is almost all used, it pushes back the piston so that new brake pads can be easily removed and replaced.