The Brakes in Your Car: Common Malfunctions, Service and MaintenanceUpdated Jan. 2, 2021
The brakes are your vehicle’s most important safety feature and your last line of defense against imminent collisions. Failures in other vehicle systems can be extremely dangerous but if the brakes are working, you will at least have a way to slow down or stop the vehicle in an emergency. If the brakes stop working while you are driving, bringing the vehicle to a safe stop will be incredibly difficult.
To protect against complete loss of braking ability, all road vehicles are built with two separate brake systems. These are:
- The service brakes, which you operate with a pedal in the driver’s footwell. These brakes are designed to slow down or stop the vehicle while it is in motion.
- The parking brake (also known as the emergency brake) which you operate with a lever situated between the two front seats of the vehicle. The parking brake is designed primarily to hold a stopped vehicle in place, though it can be used to stop a moving vehicle if the service brakes fail.
As a driver and car owner, you must have a basic understanding of how these braking systems work, how to maintain them, and how to spot the early warning signs of a brake system malfunction.
The service brakes
Most modern vehicles have separate service brake systems for the front and rear wheels so that if one fails, the other is more likely to remain operational. Pressing the service brake pedal in the driver’s footwell activates both the front and rear brakes evenly, using a hydraulic mechanism.
The service brake system consists of a master cylinder and piston, which are connected to individual “slave” cylinders at each wheel. Applying pressure to the brake pedal depresses the piston in the master cylinder, forcing hydraulic fluid along the pipeline to each slave cylinder. As the slave cylinders fill with fluid, they push pistons out to apply pressure to each wheel. The friction caused by this pressure slows the spinning wheel and reduces the speed of the vehicle.
All road vehicles use disc brakes, drum brakes or a combination of the two systems. Prior to 1970, all vehicles were produced with drum brakes. Most cars built since that time have disc brakes on at least the front wheels, as they are known to be more reliable and less prone to overheating than drum brakes. When brakes apply pressure to a spinning wheel, that wheel’s kinetic energy is converted into thermal energy. As a result, braking systems must be extremely resistant to heat.
Conventional drum brakes feature a set of brake shoes, housed in a drum that rotates alongside the wheel. When pressure is applied to the brake pedal, the brake shoes extend and connect with the spinning wheel, to create friction.
As mentioned above, this process relies on the brakes being able to absorb heat as the kinetic energy from the wheel dissipates. This heat must be released quickly, otherwise the brakes themselves will become too hot to absorb any further energy from the wheels. The trouble with drum brakes is that the drum-shaped housing tends to trap heat. When drum brakes are subject to extreme stress, they may overheat and be unable to slow the spinning wheel. Despite this, drum brakes are still frequently installed on the rear wheels of most road vehicles. As deceleration shifts weight towards the front of the vehicle, the rear wheels are far easier to slow down and stop than the front wheels.
Most modern vehicles feature disc brakes on the front vehicles. Certain high-end and high-performance vehicles have disc brakes on all four wheels, though this is relatively uncommon in ordinary passenger cars.
Disc brakes operate in a similar way to drum brakes, with one important difference. Rather than using brake shoes which are housed in an enclosed drum, disc brakes use brake pads attached to a caliper to apply pressure to the wheel. As the brake pads are exposed to the air, the heat they absorb can dissipate easily and they are far less likely to overheat.
The fluid used in the service brake’s hydraulic system is stored in the engine compartment, in a brake fluid reservoir. If the brake fluid runs low due to a leak or general wear, pressure in the hydraulic cylinders will be lost and your brakes will become less responsive. If the brake fluid runs out altogether, the brakes will not work at all.
Your vehicle’s brake fluid should not need to be replaced frequently, as it is contained in an enclosed system. However, moisture, dirt and other impurities can eventually find their way into the brake system and affect how the brake fluid works. This tends to be more of a problem for motorists who spend a lot of time driving in wet, humid or salty conditions. Your vehicle owner’s manual should tell you how frequently the brake fluid must be replaced. As a rule, it is wise to get the fluid checked out each time your vehicle has an oil change.
Service brake inspection and maintenance
Everything you need to know about maintaining your vehicle’s service brakes can be found in the car owner’s manual – make sure you read this information thoroughly. The service brake’s shoes, or brake pads, are subject to extreme heat, pressure and stress. As a result, they will eventually wear out and need to be replaced.
Regardless of which braking system your vehicle uses, it should be relatively straightforward to figure out when they need a service. Drum brakes typically include a hole at the back of the drum, which will allow you (or your mechanic) to see how worn the braking shoes are. It is even easier to detect wear in disc brakes, as they are built with a wear-indicator layer underneath their friction-enhancing outer surface. This layer is designed to make a squealing sound when it touches the spinning wheel. If your brakes start to squeal, your brake pads need replacing.
Unlike the service brakes, the parking brake only applies friction to the rear wheels of the vehicle. The parking brake operates with a simpler mechanism than the service brakes. The lever in between the two front seats is attached to a steel cable, which runs along the underside of the passenger compartment and connects to the rear-wheel drum or disc brakes. When the lever is pulled upward and the parking brake is engaged, this steel cord is pulled tight and the brake shoes or brake pads are fixed against the wheels. Releasing the parking brake by pushing the lever down will slacken the cable, withdrawing the brakes from the wheels.
Generally, the parking brake is only used to fix the vehicle in place when you are parking or coming to a complete stop. If the service brakes fail for any reason, you can engage the parking brake to slow the vehicle in an emergency. Note that it is wise to reduce speed as much as possible by removing your foot from the gas pedal, before applying the parking brake in an emergency. As this brake system only works on the rear wheels, it will have a harder time bringing the car to a stop than the service brakes.
Parking brake malfunctions
If your service brakes fail, the parking brake may be the only thing standing between you and a catastrophic road accident. You also need the parking brake to secure the vehicle safely and prevent it from rolling when parked. Any problems with the parking brake must be investigated by a trained mechanic immediately. Check out these common parking brake problems and their likely causes:
Lack of resistance in the parking brake lever.
If the parking brake lever becomes loose and does not encounter the usual amount of resistance when lifted, it is not fully engaging the rear brakes. If the resistance is gone altogether, the brakes will not work at all. This problem could indicate a malfunction in the lever, though it is more often caused by a problem with the parking brake cable. It may need to be tightened or replaced.
The parking brake will not engage.
If pulling the parking brake lever up does not engage the brakes properly, you need to get the system serviced right away. The most common cause of an ineffective parking brake is misaligned brake shoes. A mechanic will be able to adjust the brake shoes for you, to rectify the problem. The issue could also be caused by a loose brake cable, a detached brake cable, or a rusted crank mechanism beneath the lever.
The parking brake will not disengage.
Pressing the parking brake lever down should release the rear-wheel brakes. There are several reasons this may not happen, all of which will require professional service. A parking brake that will not disengage could be caused by damage to the connecting parts around the brake shoes, a seized brake caliper or a corroded parking brake cable.
Antilock braking system (ABS)
For standard hydraulic service brakes to work effectively during emergencies and sudden stops, the driver must know how to employ threshold braking techniques and must have the presence of mind to apply them. The problem with conventional brakes is that applying sudden, strong pressure to the brake pedal can lock the wheels in one position and cause pressure to be lost in the hydraulic system. This can have disastrous results, not only as the car will continue to skid along its original path of travel, but because loss of hydraulic pressure will prevent the driver from reapplying the brakes immediately.
Threshold braking is the practice of applying the brakes with gradually increasing pressure and easing off before the wheel locks. This process must be repeated until the vehicle has been slowed to the desired speed. If wheel-lock does occur in a car with conventional brakes, the driver must take their foot off the pedal to unlock the wheels, then pump the brake pedal to regain hydraulic pressure. These are challenging techniques and there is a lot that can go wrong when trying to execute them during an emergency. This is the reason that all modern vehicles are built with anti-lock braking systems (ABS).
The antilock braking system in your vehicle will manage braking pressure for you; all you need to do is press your foot firmly down on the brake pedal and hold it there. Antilock braking systems use wheel sensors that detect when the vehicle’s wheels are about to lock. Before this can happen, the system will withdraw pressure from the wheel by releasing a valve. As the wheel starts to regain speed, the antilock braking system will once again apply pressure to the wheel. This sounds like a lengthy process, but it all happens very quickly. When you apply the brakes, the ABS will pulse the brake pads or shoes against the wheel, up to 15 times a second.
Antilock braking systems make for far safer and more effective emergency braking. They also help the wheels to maintain traction during evasive maneuvers. The only downside with ABS is that the driver cannot attempt to use manual braking techniques. Never pump the brake pedal in a vehicle that uses ABS, as this will prevent the system from working.
Antilock braking system checks
A failure in your antilock braking system could result in a serious accident if you are forced to stop suddenly. This is such an essential safety system that your vehicle’s computer will automatically check it for faults every time you start the car. When you turn the key in the ignition, the ABS warning light on the dashboard will light up – this simply indicates that the computer is testing the ABS. After a few moments, the warning light should turn off. If this does not happen, the computer has detected a problem in the antilock braking system. More often than not, this is the result of an electrical fault somewhere within the vehicle. Do not continue to drive until the car until the problem has been investigated, even if the system seems to be working fine.
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