Disc brakes vs drum brakes. Differences, advantages and disadvantages.

How does the disc brake work? 

The disc brake system consists of rotor, brake pads, pistons, and brake calipers. The pistons push the pads on the rotor to slow down or stop a car. Most modern vehicles use a braking system that contains brake discs. They are so-called because they use the force applied to the discs attached to the wheels to slow down a car. Compared to drum brakes, the brake discs offer greater stopping power and do not heat up so quickly on heavy use.

While some cars still use drum brakes on the rear wheels, the brake discs on all four wheels are commonly found in family sedans, trucks and performance sports cars.

The components of the disc braking system 

  • Rotor: A circular disk placed on the hub of the wheel that rotates with it. The rotors are usually made of cast steel, but some luxury cars use a ceramic carbon rotor. The rotors are either grooved or drilled to better disperse heat.
  • Brake pads: The components that press on the rotor, creating a friction that slows down or stops the car. They are composed of the metal support and the contact surface with the brake disc. The contact surface is the worn one. It is made of different materials and can be of three types: organic, semi-metallic and ceramic. The material chosen will have an impact on the life of the brake pads, on the noise that is heard when braking and on the duration of stoping.
  • Pistons: Cylinders connected to the hydraulic braking system. The piston is the one that moves the brake pads on the rotor when the driver presses the brake pedal.  Some braking systems have a single piston that moves both plates, while others have two pistons that push the plates on each side of the rotor. Others have four, six or even eight pistons for higher braking power, but also an additional cost due to their complexity and maintenance.
  • Brake Calipers: Cases that fit over the rotor and hold the brake pads and pistons, as well as hoses for the brake fluid. There are two types of brake calipers: movable and fixed. The movable “float” above the rotor and have power only on one side. When the driver presses the brake pedal, the pistons press the brake pads on one side of the rotor, which causes the caliper to slide so that the pads on the piston-free side of the stirrup make contact with the rotor. The fixed calipers are fastened in place and have pistons on both sides of the rotor that move when the driver brakes. Fixed calipers apply equal pressure and get better on the rotor. However, mobile stirrups are found in most cars and are perfectly suited for everyday driving.
  • Sensors: Some cars have brakes that contain sensors in the brake pads. They tell the driver how quickly the pads wear out. Other brake sensors play an important role in the car’s ABS.

How do disc brakes work?

Brakes should respond instantly. When the driver presses the pedal, a piston inside the main brake cylinder puts pressure on the hydraulic fluid from the brake hoses, which move the pistons that push the pads on the rotor. The more the driver presses the pedal, the higher the pressure in the brake hoses and the pads will press harder on the rotor. The distance the pads move is very small – only a few millimeters – and it should retract back into the caliper as soon as the driver releases the pedal.

Brake disc wear

Even in normal driving scenarios, disc braking systems have a lot of effort and heat and, over time, have certain components that need to be replaced. Brake pads need replacement most often.

When this happens, it depends on your driving habits and the material from which the plates are made but varies between 40,000 km and 120,000 km. Brake rotors withstand between 90,000 and 110,000 km (sometimes more) but can be damaged if they overheat or if the pads are not changed in time. The brake fluid is the blood of the entire braking system, so check it between 38,000 and 57,000 km, or if you suspect a leak. The pistons and calipers should withstand the entire life of the car unless there is a mechanical problem and they are destroyed by debris on the road or in an accident or due to inactivity.

Symptoms of brake disc problems

A few hard to ignore signs warn the driver that there is a problem with the brakes.

  • Scrapings: When the contact material of the pads is worn, an indicator of wear inside the pad comes into contact with the rotor, producing a sharp scratch. Replacing the brake pads usually eliminates noise, but it may also be caused by road debris trapped in stirrups.
  • Pedal shaking or vibrating: If the brake pedal shakes or vibrates when pressed, there is a chance that the rotor will be deformed. The brake rotors must be perfectly flat and their deformation may occur due to overloading or overheating. The rotors can be refined to make them fine again, although their immediate replacement is just as expensive, but safer.
  • Low brake pedal: The pedal should feel good on the foot, with the braking force proportional to the amount of pressure applied to the pedal. If the pedal is feeling lower than usual, it is often a sign of contamination of the brake fluid or leakage from the system. Its air and water in the liquid reduce its efficiency, and a leak is a serious problem. Ask a mechanic to change the brake fluid or check the leakage system to restore full braking power.

Brakes are the most important car safety system, and the brake discs offer a powerful, reliable and durable performance. Chances are your car will have such a braking system, so be careful of any unusual signs that might indicate that a part needs to be replaced.

Drum brakes

Many cars now have disc brakes on the front axle and drums on the back. Why is this combination used? First of all, for reasons of lower costs. Why have two more brake calipers, two discs and two pairs of brake pads installed on a car that doesn’t need them? Cars with drum brakes on the back are low power in general or are not made at all for high speeds.

In most cars, braking is done almost entirely on the front axle. You can convince yourself when you have a car with discs on all wheels, with which you have not driven for a few months and you have rusty discs. After an hour’s drive through the city, you’ll see that the front brake discs are clean, but the rear ones still carry the rust. Precisely because they are not so requested. The same is true of cars with discs on the front and drums on the back, the drums are sufficient to brake that car.

How do the drum brakes work?

The drum braking system includes the drum, the brake shoes, the wheel cylinder. The cylinder pushes the shoes on the drum to slow down or stop the car  Some cars have partial drum braking systems. They are so-called because they use the friction applied to the metal drums attached to the wheels to slow down or stop the car.

While disc brakes offer better braking performance and have become common in modern cars, drum brakes are still used in some cars, mostly as a partial braking system. They can be found on the rear wheels of cheaper cars and classic cars.

Components of the drum braking system

  • Plate: Provides a solid foundation for the other drum brake components. It is attached to the shaft.
  • Drum: Caught on the wheel hub it spins with it. Often made of cast iron, it is resistant to heat and wear. This is what you see on an assembled drum brake and is the component on which the braking force is applied to slow down or stop the car.
  • Cylinder: Contains two pistons, one at each end, which operate the brake shoes. The cylinder applies pressure on the piston, which pushes the shoes to the drum, slowing or stopping the car. A cylinder is required on each wheel.
  • Brake shoes: Press on the drum to create the required friction to slow down or stop the car. Griped, but able to slide when the pressure in the wheel cylinder is applied. They have a coating material made of organic or metallic components. This coating material comes in contact with the drum and wears out over time. Each brake has two brake shoes. The main block is in front and the second in the rear.
  • Automatic regulator: Keeps the shoes at a fairly large distance from the drum, even when the material is worn out.
  • Springs: Pull the shoes back from the reels when the driver releases the brake pedal.

Drum brake wear

Drums and brake shoes should be the only components to be replaced in a drum braking system. The block’s covering material wears out over time and, in general, new brake shoes should be fitted every 56,000 km, although this depends on your car and your driving habits.

Otherwise, the wheel cylinder, automatic regulator and springs should last the entire life of the car, although mechanical problems or damage due to road debris or an accident are possible. However, it is good to check the brake fluid every 38,000 – 57,000 km and immediately if you suspect a leak.

How do the drum brakes work?

Brakes should respond instantly. When the driver presses the pedal, the piston in the brake master cylinder presses the hydraulic fluid from the brake hoses, which then pressurizes the wheel cylinder and pushes the shoe on the drum.

The more the driver presses the pedal, the greater the pressure inside the brake hoses, and the more the shoes will be pressed on the drum. The distance the block moves is small and the springs should retract them back from the drum as soon as the driver releases the pedal.

Hand brake with drum

Some vehicles have disc brakes on all wheels but use a small drum brake inside the wheel hub assembly as a hand (or parking) brake. When the hand brake is applied, a lever attached to a cable forces the brake shoes It offers direct control instead of passing through the wheel cylinder or the hydraulic part of the brake which allows the vehicle to stop even when the usual brakes are no longer functioning.

Signs of drum brake problems

There are several signs that the driver announces that there are problems with drum brakes.

  • Brake noise: As the brake shoes wear out over time, excessive or unusual noise may indicate that the coating material is worn. A technician can check why the brakes are making noise, and replacing the shoes often solves the problem.
  • A pedal that shakes or vibrates: If the brake pedal vibrates or shakes when pressed, there is a chance that the drum will be deformed. The drums must be perfectly round and deformation can occur due to overheating or overheating. In general, their replacement solves the problem and the braking is normal again.
  • Low brake pedal: The brake pedal should feel good at the foot, with a braking force proportional to the amount of pressure applied to the pedal. If the pedal feels lower than usual, it is often a sign that the brake fluid has been contaminated or there is a leak in the system.
  • Water or air in the brake fluid reduces its effectiveness, and leakage is a serious problem Have a technician check your fluid or inspect the leakage system for normal braking power. A damaged brake cylinder can also be the culprit for a low brake pedal.

Brakes are undoubtedly the most important safety system of a car, so be careful of any unusual signs that might indicate that a part of the drum braking system needs to be replaced.

The advantages of the brake discs

First of all, you can look at discs without disassembling the wheel if the pads or discs have worn out. The most important advantage of the discs, however, is that they have a much greater braking force because the surface exerted by the two plates is larger than a shoe. The advantages continue with the fact that thermal energy dispersion is better when we have discs. And, last but not least, the disc brakes can be adjusted according to the hydraulic pressure and the braking force distribution.

As for disadvantages, it is clear that the advantages of one system represent disadvantages for the other, so we do not list them anymore. But we need to know exactly what interests us. And with the brakes they are just about safety, you have to brake well, which is why the discs are more popular nowadays.

So, are rear disc brakes worth it?

Yes and no. If your goal is to buy a fast car, or you drive faster, then disc brakes on the back are necessary. Fast cars always come from the fabric equipped with rear disc brakes, but, if you are not interested in speed and you want to get from point A to point B, or you drive a lot in the crowded city, then a car equipped with drums on the back is enough.

The advantages of the brake drum

From the head of the place, it is clear to everyone that drum brakes do not have as many advantages as those on the disc, otherwise, all cars would still have them. But they still have some advantages. As if the whole braking system is locked in the drum, that is, away from moisture, dust, sand or impurities from the streets.

From here comes the next advantage: they are much more durable than those on the disk, resisting without interventions even 200,000 kilometers. And the last advantage is that they have a low price compared to the discs, but also easy to change at the revision because they are replaced much faster.

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