Brake Caliper Explained: How It Works and Why It Matters

What is a caliper, why is it needed, how is it constructed, and what are the dangers of it failing? We answer the main questions about one of the most critical components of the braking system.

Brake caliper. Photo: Shutterstock

What is a caliper?

A caliper is a component of a vehicle's braking system that presses the brake pads against the brake disc when the brake pedal is pressed. In essence, the caliper is one of the most important mechanical parts of the braking system, which, along with other parts, is responsible for effectively slowing down the vehicle during braking.

It is a device consisting of pistons connected to the hydraulic part of the brake system, to which the brake pads are attached. When the driver presses the brake pedal, brake fluid is supplied under pressure through the brake system lines to the caliper. It presses on the piston, which in turn moves out of the caliper housing and presses on the brake pads, pressing them against the disc.

Brake caliper

Despite its essential function, the brake caliper is not that complicated in terms of design.

It consists of a piston or several pistons connected to the hydraulic brake system, to which the brake pads are attached. The location and number of brake pads, as well as the method of attaching the caliper to the hub, may vary. However, the general design of all systems is virtually identical and consists of:

A housing
A cylinder with one or more pistons
Guides
Piston guide dust covers
Piston mounting and sealing rings
Brake pads
Brake lines with fittings
Return springs
A floating caliper.

Despite its important function, the design of the caliper is not particularly complex

Despite its essential function, the design of the caliper is not particularly complex. (Photo: Shutterstock)

Types of calipers

Depending on the design of the caliper, there may be more than one piston exerting pressure on the pad. Sometimes two or more are used. The type of assembly also depends on the location of the pistons in the caliper. There are two types of calipers:

Fixed

If the pistons in the caliper are located on both sides of the disc, it is called a fixed caliper. Structurally, such a caliper is a metal housing in which several cylinders are symmetrically arranged. Each of them has pistons. When moving, they press both pads against the disc at the same time. The caliper body itself is rigidly attached to the suspension components. When at rest, the pads inside the caliper are held in place by special springs.

With a floating caliper

If the pistons in the caliper are only installed on the inside of the brake disc, this is usually a floating caliper. In this case, the piston or pistons only press on the inner pad.

Under their influence, the pad is pressed against the disc, and the caliper moves along the guides and presses the second outer pad. This is the simplest design used on most budget cars, as it is significantly cheaper to manufacture. However, such calipers are inferior to fixed calipers in terms of efficiency.

Front and rear brake calipers: what is the difference?

In reality, there are no significant differences between them, as the calipers on both the front and rear axles operate on the same principle. However, there are slight differences in nuances due to adaptation to different operating conditions.

The calipers located on the rear axle are slightly modified, as they also have to work with the parking brake. Rear calipers are somewhat larger than front calipers and have a slightly more complex design, as they are equipped with an additional drive from the parking brake. Accordingly, due to the design features of the parts, it is not possible to install a front caliper in place of a rear caliper and vice versa.

When to replace a brake caliper

Like any other part of a car, a caliper is subject to wear and tear and can fail. In the next chapter, we will discuss the most common malfunctions and their causes. But first, let's look at the main signs of caliper malfunction.

Squeaking when braking

Squeaking when braking can be a sign of other brake problems. For example, if sand has gotten into the discs or the pads are worn out. But if you know that you haven't driven on dirt roads and your pads are new and have been replaced recently, squeaking when braking may indicate a problem with the calipers.

Like any other part of a car, brake calipers are subject to wear and tear and can fail

Like any other part of a car, brake calipers are subject to wear and tear and can fail. (Photo: Shutterstock)

Brake fluid leak

Another sign of a malfunction is the appearance of brake fluid on the discs or stains on the ground near the wheels. In general, brake fluid leaks can occur in any area of the brake hoses and lines, but this often happens where the pipes connect to the calipers.

Brake sticking and seizing

Sometimes the calipers activate when compressed, pressing the pads against the disc, and do not return to their original position afterwards. This is the first sign that the piston or guides may be seized.

Soft brake pedal

Another symptom that can indicate completely different problems with the brake system, but is also one of the main signs of caliper malfunction.

Overheating

Another sign of caliper malfunction may be overheating of the brakes. This includes both the pads and discs, as well as the brake fluid.

Uneven pad wear

Another sign indicating a caliper malfunction, in particular, is problems with the piston or guides.

Causes of caliper malfunction

So, what kinds of malfunctions can occur in a caliper, and what causes them? In principle, there is only one major malfunction that can happen in a caliper: loss of mobility of the piston or caliper guide bracket.

However, the causes of this malfunction can vary. The following factors can cause them:

Untimely replacement of brake fluid
Wear and tear of dust caps
Corrosion of parts: floating caliper, guides
Piston seizure
Damaged hoses or fittings

Summary

The caliper is a key component of the braking system that presses the pads against the disc to slow down the vehicle.
How it works: Hydraulic pressure from the brake pedal pushes the piston, which compresses the pads.
The caliper design - includes a housing, pistons, guides, dust covers, pads, lines, and fasteners.
There are two main types of calipers:
Fixed – pistons on both sides of the disc, high efficiency.
Floating – piston on one side only, cheaper but less efficient.
Front and rear calipers differ in design due to the parking brake (rear calipers are more complex and larger).
Signs of malfunction: squeaking, brake fluid leakage, jamming, soft pedal, overheating, uneven pad wear.
The main malfunction is the sticking of the piston or guides due to corrosion, wear of the dust caps, or old fluid.