Brake calipers are part of the disc braking system used on most modern cars. The entire system consists of the rotor, caliper, and pads. The caliper itself is the actuator that presses the pads to the rotor to stop the vehicle. The caliper is controlled by hydraulic pressure through brake lines attached to the vehicle's brake master cylinder.
Understanding the Braking System
The braking system itself works in this sequence:
- The brake pedal is compressed
- The master cylinder pressurizes hydraulic fluid ("brake fluid") through the lines to each of the vehicle's wheels
- The brake calipers to push their pistons towards the brake rotor
- The brake pads, which are attached to the caliper, are pressed into the rotor
- Friction slows and stops the car because the rotor is attached to the wheel itself
The brake calipers are the muscle that make the braking happen.
There are two types of brake caliper, floating and fixed. Fixed brakes are most common on today's vehicles, though they are more expensive, but floating calipers are not unusual. Fixed calipers work by compressing the pads towards the disc from both sides at the same time, with the caliper itself remaining fixed. Floating calipers work by pressing one side into the caliper and then pulling the other side to match once the primary side has stopped against the rotor. These are prone to failure, but are cheaper and simpler to produce and install.
Either caliper type will have one or more pistons which do the actual work. These pistons are actuated by brake fluid (hydraulic fluid) being sent into the chamber behind the piston, pressing it outwards. When the pressure is relieved, the pistons naturally pull back to their original position, taking the brake pads away from the rotor disc.
The Bottom Line
Brake calipers are simple machines and require little maintenance beyond changing the pads and the occasional lubrication of the pistons. It is not uncommon for floating calipers to have a maintenance interval that requires they be removed, disassembled and cleaned, and re-assembled with new seals and lubrication. Fixed rotors rarely require anything that costly or time consuming, but are far less tolerant of rotor imperfections, since they cannot move alignment to match the rotor itself.