Disc brakes rely on brake pads that squeeze the rotors to bring wheels to a stop, and the brake calipers transfer power from the brake fluid to the pads so this can happen. The vast majority of newer vehicles are fitted with disc brakes in the front of the vehicle, and many are beginning to replace rear-wheel drum brakes with disc brakes as well. Essentially, when the driver presses the brake pedal, fluid travels to the calipers, which are fitted around the brake pads. They transfer the force of the pressurized fluid into the brake pads.
Calipers are mounted to the brake system in two main fashions - floating and fixed. The latter is bolted to the spindle and has no mobility. Floating calipers are also attached to the spindle, or the backing plate, but they are fastened with a slide bolt. This affords the calipers a bit of movement. The floating design also only involves one or two pistons on one side of the part, which push the caliper when the brakes are activated. Fixed placement calipers have one to six pairs of pistons on both sides. This type typically offers better performance than floating calipers.
Regardless of type, the pistons must be properly sealed to prevent brake fluid from leaking. Main piston seals serve this purpose while still allowing the pistons to move back and forth. The seals are covered by dust seals to protect them from exterior damage.The brake fluid travels to the caliper by way of a high-pressure brake hose, but even if everything is sealed, air might still find its way into the system.The caliper has a built-in brake fluid bleeder that is designed to remove any air that may have gotten into the lines, which could otherwise lead to brake failure.
Other issues can arise with the calipers as well. A sticking caliper can cause the wheel to slide when the brakes are applied, which can make it more difficult to bring the vehicle to a stop. It also leads to the brake pad being stuck against the rotor, which causes unnecessary wear of the pads and the brake disc.
If the sticking is severe, drivers may notice that the vehicle pulls to one side when driving. This is because one or more wheels are being slowed down unnecessarily. This issue may also be caused by other things like alignment or an issue with the steering system. When letting go of the steering wheel for a moment results in the vehicle changing direction, chances are that the calipers are the root of the problem.
Worn brake pads can also have an adverse effect on the calipers. They will adjust their position to compensate for pad wear, and will need to be reset to ensure they function correctly and there is enough room for new brake pads. They can also get caught on the calipers if they are not properly lubricated, which will cause sticking. This is evidenced by an uneven wear across the brake pad.
Drivers who suspect that the brake calipers on their vehicles are failing can check for signs that this is the case by feeling the temperature of the brakes after a drive. When heat can be felt coming off of the wheels, this could be caused by the friction generated by the constant drag on the rotor due to a sticking brake caliper.