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Home >   How To >   How to Repair Brake System >   What is a Brake Caliper?

What is a Brake Caliper?

Braking is a very straightforward process: friction between the brake rotor, a rotating component, and the brake pad, a stationary component, causes the rotor to slow down or stop spinning. The brake caliper houses pistons which aid in pushing the brake pads against the rotor.





Single-Piston And Multi-Piston Calipers


Many calipers used in road cars utilize a single sided design on their sliding pins. This means the piston(s) are located only on one side of the caliper, usually on the side of the brake disc. This enables the caliper to extend and press against the brake disc. This in turn causes the whole caliper to slide on the pins and pull the opposite pad onto the disc, as well.


A better option is to have at least a pair of pistons, one on each side of the caliper forcing the pads onto the disc evenly. However, this inevitably increases the thickness of the caliper, which can cause problems with the space behind the wheel. The number and size of the pistons in the caliper are chosen by the manufacturer to the match the car's specific features. For example, a heavy car may have four-piston calipers to allow a bigger pad to be used to generate a greater braking force.


As a rough rule of thumb, a four-piston caliper can handle a 131 mm-long pad while a six-piston version will allow a 152 mm-long pad. Because the amount of friction generated is directly related to the size of the pad, contact area and the force clamping it, a bigger pad provides stronger brakes, with all forces being equal.


Another benefit of multiple-piston calipers is a resistance to pad tapering. While braking, the surface of the pad gets hot and if it gets too hot, the material can begin to melt. As it does so, it begins to flow in the same direction as the rotation of the disc. This in turn leads to the pad becoming wedge-shaped. So, a smaller piston at the leading edge of the pad and a larger one at the trailing edge will provide more force to the area where the material builds-up and help keep the pad flat against the disc.


Common Problems of a Brake Caliper


  • The brake calipers have O-rings to keep the brake fluid from leaking out of the system. The seal may wear out over time, causing the fluid to seep out. This is one of the common problems in the brake caliper. The brake fluid can also leak due to bad bleeder screws.
  • Sticky brake pads can be another dangerous problem with your brake caliper. This can be due to jammed or stuck or frozen pistons.
  • The caliper can also develop corrosion, failing to provide an efficient braking performance.


Symptoms of a Damaged Brake Caliper


  • If your car tends to list towards one side while braking, it indicates that the brake calipers have gone bad. The harder you brake, the harder the car pulls towards one side.
  • Traces of brake fluid around the brake caliper and rotor indicate a fluid leak due to the caliper.
  • A stiff or soft brake pedal may be due to a sticky caliper.
  • The brake warning indicator in your automobile's instrument cluster will also light up.


When you experience the aforementioned symptoms, give your brake caliper a thorough look-over and have the faulty caliper replaced at the earliest, if required. If you are confident about replacing the brake caliper on your own, follow the necessary safety precautions specified in your user's manual. Be sure to lubricate the sides properly and not to over-tighten the bolts. Otherwise, it is always a better practice to get the faulty brake system fixed by a certified mechanic.


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