Brake systems are a complicated but necessary part of any vehicle. While it is clear that a braking system’s primary function is to ‘stop’ a car, there are different methods and components that accomplish this same function. This is made clear as technology advances, with specific braking systems becoming more prevalent in modern cars, and others fading into obscurity.
The main three brake systems found in modern cars are frictional, electromagnetic, and hydraulic.
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Frictional or ‘mechanical’ Brake Systems
The mechanical brake system is also known as the ‘manual’ or ‘hand’ brake used for parallel parking, and emergencies. The use of fulcrums, levers, and springs carries brake force to the associated drums or rotors in order to stop the car. The resulting energy is primarily frictional and is typically used as a last resort in brake failure.
Electromagnetic Brake Systems
Electromagnetic brakes have commonly been used in trains, but are now also becoming popular in modern electric and hybrid vehicles. Electromagnetic brakes utilize magnetic resistance to clamp two brake discs together.
This system consists of two brake discs that are separated by a thin air gap. One disc is moving with the wheel, while the other is static, but is modified to have magnets in it. When an electrical charge is transmitted to this magnetic disc, it creates an opposing force that instantaneously clamps both faces shut. The resulting friction creates the power needed to stop motion. A research paper describes the process as using the,
“Principle of Electromagnetism is used in the Electromagnetic Braking system. When a certain amount of current is passed through a round conductor then it produces a magnetic field which is uniform all over the conductor.” (Wagh et al, 2017)
Electromagnetic brakes are known for their efficiency and very responsive braking.
Hydraulic
Hydraulic brake systems are what most modern cars use. In this system, tubes filled with brake fluid known as the ‘master’ and ‘slave’ cylinder are used to create stopping force through liquid pressure. Pressing the brake pedal compresses the specialized brake fluid, which in turn creates pressure. This resulting pressure travels to the slave cylinder with enough force to cause brake pads to expand. This, in turn, stops the car.
Servo Brake System
Servo brakes are not systems in themselves. However, they serve as a tool that assists in braking through the use of vacuum pressure. When the brake pedal is pressed, the piston pushes this internal seal forward, which in turn is what triggers the pressurized vacuum. In other words, this vacuum amplifies the braking force of the driver. Likewise, once the pedal is let go, the pressure dissipates as the internal valve goes back into its resting position.
ABS (Anti-Lock Braking System)
ABS brake systems are a common addition to new vehicles, and offer a new standard of safety. The main purpose of ABS systems is to prevent brakes from locking in the event a driver has to slam on the pedal during an emergency situation.
While braking, the threshold for maximum efficiency is right before they become locked. Before ABS, a technique known as ‘cadence braking’ was used by drivers to prevent skidding, which is what ABS does automatically. Cadence braking is a fine balance to strike, as not braking enough may not stop the car in time, and braking too hard will create a skid.
ABS uses electronic impulses and valves to repeatedly trigger the brake system in order to keep wheels at zero rotational force. This prevents the steering wheel from locking and allows the driver some control during a skid. The ABS determines where to put the brake pressure, so the driver can focus on re-aligning the vehicle out of harm’s way.
Brake systems explain the mechanics of what causes stopping force, usually two metal faces expanding or clamping together. However, two kinds of actual brakes are used in vehicles. These are Drum brakes and Disc brakes, respectively.
Drum Brakes
Drum brakes are hollow cylinders attached to a piston and wheel, with two ‘brake shoes’ in the centre. The outer layer spins while the vehicle moves, unaffected by the shoes until the brake is pressed. By force enacted by a particular braking system, the interior brake shoes expand against the outer rotating drum, causing friction. A lot of heat is produced from this, which is why the drum’s interior is left mostly hollow.
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Drum brakes are almost exclusively used for the back wheels.
Disc Brakes
Disc brakes are made up of a rotating disc known as a ‘rotor,’ a calliper, and brake pads. The calliper is a slightly curved metal object that houses the brake pads and helps enforce pressure to squeeze them against the rotor. Disc brakes are located at the front of a car because of their higher performance compared to the drum brakes.
Brake Pads and Materials
Braking is an intense and destructive process due to the amount of heat produced from friction. Unsurprisingly, brake pads are not meant to last forever. However, they certainly perform long enough without causing damage to the vehicle. This is possible because of the three kinds of brake pad materials manufactured for resisting frictional wear and tear.
Brake Fluid
Types of Brake Fluids
There are a few types of brake fluid, each differing in their boiling point. The differences are marked by how much performance is needed, with most of them being only useful in sports racing. This difference in performance is characterized by differences in boiling points, with higher boiling points indicating use for higher-performance vehicles.
Additionally, there is the ‘dry’ and ‘wet’ boiling point. Dry boiling points refer to the heat resistance of brake fluid fresh out of the bottle. Wet boiling points refer to the expected boiling points after being ‘contaminated’ by water from use. This is the reason brake fluid must be replaced every two years.
The following is a list of brake fluid grades,
DOT 3
Dot 3 fluid is used in most cars, as it is suitable for day-to-day braking and driving. Dot 3 Brake fluids have a boiling point of 190 °C (374 °F) and a wet boiling point of 140 °C (284 °F). Dot 3 has a glycol ether base.
DOT 4
Dot 4 has a dry boiling point of 230 °C (446 °F) and a wet boiling point of 155 °C (311 °F). Dot 4 has a glycol ether and borate ester base.
DOT 5
Dot 5 has a dry boiling point of 260 °C (500 °F) and a wet boiling point of 180 °C (356 °F) Dot 5 differs in its unique silicone base, which is not compatible with other fluids, and some brake systems.
DOT 5.1
Dot 5.1 has a dry boiling point of 260 °C (500 °F) and wet boiling point of 180 °C (356 °F). In terms of performance, it is identical to Dot 5, except that it has a glycol ether/borate ester chemical base. Brake fluids with separate bases are not compatible, which also sometimes applies to specific braking systems.
How Often Should You Change Brake Fluid?
Brake fluid does not last forever, so it is important to remember when to replace it. Ignoring this regular part of the maintenance can result in brake fluid that absorbs too much moisture, reducing its overall capacity to function correctly. The cost of this negligence could be your own life, if untreated for long enough.
This is because even in air-tight brake lines, brake fluid will slowly begin to absorb condensed moisture over time. More moisture ‘pollutes’ brake fluid by reducing its resistance to heat, causing it to bubble. Trying to use the brake on this fluid will result in the condition known as ‘sinking brake’ where there is not enough pressure generated to stop the car.
Brake fluid usually lasts for two years. However, other conditions may shorten this lifespan. A general rule is to be aware of brake performance and check the fluid every time you go in for an oil change.
Signs of brake fluid gone ‘bad’ are the following,
- ‘Dirty’ or brownish yellow colour
- Bubble in the fluid
- Burning smell
- ABS light turns on
How is Brake Fluid Changed?
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Brake fluid is changed through a process known as ‘bleeding the brakes,’ which involves pumping out older brake fluid from the brake lines. This can be done using a pump, or by dispensing new brake fluid into the lines. Due to the consistency of the liquid, new fluid will uniformly push out the older waste.
For this to work correctly, brake lines should only ever be replaced with the same brake fluid, or fluid compatible with your car’s system. Some fluids are incompatible with specific braking systems due to their chemical composition. Dot 5 is made from silicone, which cannot mesh with Dot 3, for example.
Sometimes some problems can occur in a brake system as a result of either ageing or physical damages. Here is a list of some terms associated with a need to replace brakes.
Worn-out Brake pads
Consistent use of brake pads will eventually lead to them becoming useless. This is intentional,
as brake pads have a protective layer that is meant to wear down efficiently to prevent damages to other parts of the vehicle. When friction occurs, these protective pads disperse as a harmless powder. Overall, brakes usually last 1-2 years and create tell-tale signs when they are nearing their end.
Leaking Brake Fluid or ‘Soft Brake Pedal.’
Leaking brake fluid can occur if brake lines are damaged and pose a severe problem. The stopping power behind hydraulic brake systems comes from the pressure that is generated by this low-boiling point fluid. If the lines are cut, or if the lines are polluted with water, the brake fluid loses its resistance to heat. Without this, there is no pressure, and thus no way to stop the vehicle.
Hard Pedal
Hard brake pedals can occur because of a lack of vacuum pressure. As mentioned in the servo braking system section, vacuum-assisted brakes make braking easier by using force on the master cylinder. This is caused by two separate amounts of air separated by an internal seal. One side of the seal’s air is generated by refuse from the engine. However, if not enough is produced or there is a leak, the vacuum cannot work. The result is increased resistance in the brake pedal.
Frozen Caliper
A frozen calliper describes a situation in which the brake pads are squeezed against the rotor, and don’t completely retract. What results is the brake being lightly applied at all times due to the mechanism being ‘stuck’ or ‘frozen.’
Besides causing additional stress and reducing the lifespan of brake pads, frozen callipers can include other negative symptoms. Such symptoms include the vehicle steering more to one side and increased heat generated from constant friction. Neither of these is good, and can cause severe damages to the rest of the vehicle.
Warped Rotor
One of the possible consequences of a frozen calliper is a warped rotor, caused by damage to the rotor from excessive heat. A warped rotor is known for being uneven due to either denting or melting, which creates vibrations in the steering wheel. The more serious the deformity, the more evident the vibrations will be.
Brake maintenance is essential for getting the most use out of your car’s braking system. While they inevitably need to be changed as a regular service, some steps can be taken to avoid unnecessary wear and ageing.
- Avoid Sudden stops. Try to coast and not ‘ride’ brakes
- Avoid driving on rough terrain that can damage the underside of your car
- Pay attention to dashboard lights. Do not ignore them
- Pay attention to strange sounds and vibrations
- Have brakes serviced as part of routine car maintenance
Brakes are typically replaced for every 30,000 to 70,000 miles as a general rule of thumb. Alternatively, most other parts of braking systems like the brake fluid need to be changed every two-four years depending on the grade and moisture control. Thus having brakes serviced as a whole every two years is a good middle-ground.
The cost for brake services varies depending on the mechanic or institution providing it. In general, however, replacing both pads and rotors can range from 250-300$ per side. This is taking into account the average cost of new parts and labour. An estimate and list of brake services can be found here.
Wagh, Sagar, et al. “Electromagnetic Braking System in Automobile.” International Journal of Trend in Research and Development, vol. 4, no. 3, 2017, pp. 228-231. Itjrd.com, DOI: 2394-9333.http://www.ijtrd.com/papers/IJTRD3843.pdf
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