Brake calipers, unfortunately, don’t benefit from having a name that makes their function obvious. Fortunately for us, calipers are pretty easy to understand – they have multiple pieces, but the overall goal of a caliper is a simple in/out motion.
With that being said, what’s a brake caliper? A brake caliper is a U shaped bracket that fits over the edge of the rotor. The two inside edges of the caliper hold the brake pads and pistons. When the brakes are activated, the piston pushes the brake pads against the spinning rotor, slowing it and the wheel to a stop.
Calipers are usually included whenever someone makes a general statement about their brakes, but the calipers themselves are an extremely important and indispensable part of a vehicle’s disc brake system. Nothing in the disc brake configuration would work without them.
There is another article on this website about the function of calipers. Some of the information is the same, but repetition is the key to understanding, and there’s nothing wrong with understanding your brakes. Feel free to check it out: What Is A Brake Caliper?
What Are Brake Calipers
It may help to understand the individual pieces of a disc brake and how they work together to understand the function of a brake caliper.
The rotor is a circular piece of metal that rotates with your wheel. The wheel and the rotor always spin together and stop together. You could easily say that the rotor is just another part of the wheel.
The brake pad is the piece that pushes against the rotor when you apply the brakes. The friction between the rotor and the brake pads is what slows and stops your vehicle.
The caliper is shaped like the letter “U” and fits over the edge of the rotor. The two inside edges of the caliper hold the brake pads. When the brakes are activated, the piston pushes the brake pads against the spinning rotor, slowing your car to a stop.
Parts of Caliper
- Pistons are typically made from plastic, aluminum, or chrome-plated steel. This is a cylindrical piece of metal that moves in and out of a hole. Just like a circular button, but pushed out, rather than pushed in.The brake pads are attached to the end and are pushed against the rotor when the piston is pushed out.
- Brake Fluid is just hydraulic fluid. When the brake pedal is pushed, that force is multiplied, then applied to the brake fluid. This fluid then transfers that force to the pistons that push out the brake pads.
- Seals prevent brake fluid from leaking out of the caliper. If brake fluid leaks from anywhere you run a risk of not having working brakes. Manufacturers limit this risk by having split brake systems, so two of the four brakes will likely work if there is a leak.
- Brake Pads are the friction material that are attached to the pistons on one side. When the brake pads are pushed out, they move toward the spinning rotor and push against it, creating large amounts of friction that eventually slows the car to a stop.
Different Types Of Calipers
Calipers tend to come in two main types: Fixed and Floating.
Floating calipers (also known as “sliding calipers”) only have the piston(s) on one side. When the piston extends, the brake pad on the piston side makes contact with the rotor first.
With this in place, the piston continues to push, which pushes the caliper body away and pulls the brake pad on the other side toward the rotor. When the body is done moving, the pads on both sides are applying pressure to the rotor.
When the piston retracts, the brake pad on the other side loses contact with the rotor first, then the brake pad on the piston side follows suit.
With the caliper body being loose and mobile, some imperfections on the rotor will be have less severe consequences, though the rotor defects will still need to be fixed promptly.
Fixed calipers have two main differences:
- They have pistons on both sides
- The caliper does not move when the pistons are activated
When the pistons move, the brake pads make contact on both sides of the rotor and slows the car to a stop. The lack of mobility for the caliper body means that rotor imperfections will have more severe consequences and will need to be fixed with more urgency.
This configuration is also more complex and expensive, but can also apply more braking power and can have a better “feel” than a floating caliper.
Floating calipers tend to be good enough and are more common in lower end cars, while fixed calipers are used whenever higher performance is desired, or in heavy vehicles that need more stopping power.
Potential Issues
Leaking Brake Fluid
Time heals all wounds. It also inflicts a ton more. Time and heat will, sooner or later, lead to a failing caliper seal. The seal helps to keep the brake fluid contained, and any failures can easily create compromised brakes. You may notice the leaking brake fluid creates a puddle underneath your vehicle.
If a failure like this happens, you’ll likely still be able to use half of your brakes, but lost brake fluid is an emergency that needs to be fixed immediately.
Reduced Braking Ability
Aside from leaking fluid, your vehicle may have less braking power if the sliding function on the caliper gets stuck due to foreign materials (dirt, grime, etc.) building up in the caliper.
This will prevent the vehicle from being able to brake properly and extend the braking distance.
Unexpected Or Uncommon Braking Sounds
There are several things that might cause unwanted noise while braking. It could be that the bake pads are worn down, and the high pitched noise is caused by the wear indicator – a tiny piece of metal that scratches the rotor to alert the driver.
This or other noises could also stem from a caliber sticking or becoming too loose. These issues will only get worse with time and continued driving.
Remember that defects in the rotor can potentially cause issues with the calipers – especially with fixed calipers. The rotor surface needs to be smooth and uninterrupted.
If the rotor deforms for any reason, the brake pads and calipers will constantly move and vibrate when they clamp onto the spinning rotor. This will create vibrations and lead to much larger issues in the future if left unresolved.
Unintentional Swerving
If a caliper becomes seized, it won’t be able to retract properly. This can force brake pads to constantly drag on the rotor, even when the driver isn’t using the brakes. The wheel with the dragging brake will travel slower than the others, and the vehicle will pull to that side.
Hopefully this doesn’t need to be said, but we’ll say it anyway: fix this asap.
Low Brake Pads
While low brake pads aren’t exactly a caliper problem, like rotor defects, they can create caliper issues if they’re not fixed in a timely manner. Without the brake pads to act as a buffer, metal will be grinding on metal whenever the brakes are engaged.
This is not supposed to happen and will slowly (or quickly) destroy everything in the affected area. The cost of new brake pads is a lot smaller than the cost of new rotors and calipers. Change your brake pads when they need to be changed.
Do all Brakes Use Calipers?
Most brakes in modern vehicles use calipers. These are only used in a brake style called the disc brake, which uses a rotor (a metal disc) that spins with the wheel.
Drum brakes are a completely different configuration. These have two braking pads that press on the inside of a cylinder that rotates with your wheel.
Drum brakes were commonly used in the front and back of much older cars and trucks. They can still be found in less expensive modern vehicles, but typically only for the back wheels, while disc brakes will be used in the front. The only exception to this is very large vehicles like buses and 18 wheelers.
The caliper-equivalent on a drum brake would be a wheel cylinder.