Among the various components and systems that make up an automobile, brakes receive the least attention. Few drivers ever think about the brakes until a problem demands their attention in some seriously dangerous way. The subtle signals that indicate a potential brake problem are easy to ignore. The consequences of brake failure can be deadly. This short article will explain in basic terms what makes up the brake system of an automobile and provide some pointers to help keep drivers and passengers safe from catastrophic brake failure.
Brake systems consist of several components common to all automobiles. The brake pedal is the only part of the system most drivers ever see. The brake pedal is mechanically linked to a small hydraulic pump called the master cylinder. The output from this pump is delivered to each wheel through metal and rubber tubes called brake lines. At each wheel, a small hydraulic cylinder transfers the pressure from the master cylinder to mechanical components that stop the car. The combination of small cylinder and mechanical components at each wheel is called the caliper. Within the caliper assembly, the brake pads are actually responsible for stopping the car. Attached to each wheel and rotating with it is the rotor. In the caliper, the pressure from the master cylinder is used to force the brake pads into contact with the rotor. The friction between the pads and rotor slows the rotation by converting the rotation energy into heat.
In slightly more technical terms: the hydraulic pressure from the master cylinder produces friction at the wheels to convert the rotating motion energy of the rotors into heat. This principle is important to understanding how and why brake systems fail. Friction and heat are both the result of braking and the enemy of brake system components. The basic components are the same for all automobiles. There are some additional or related devices found in brake systems but brake problems almost always involve the basic parts discussed here.
Since brake pads use friction to convert rotating energy into heat, the point where the friction occurs is the primary wear point. Brake pads are made of materials with special properties. The materials must be extremely heat tolerant because every time a car is slowed or stopped the pads get very hot. While being heat tolerant the pads must also provide a high level of friction to the rotor. In almost any other mechanical component, friction is not a desired characteristic. Brake pad material is the opposite. Brake pads must be wear resistant along with the heat resistance and high friction properties.
All brake inspections begin with checking the wear on the brake pads. As pads wear down they become less able to dissipate the tremendous heat they produce. Excessively worn pads will cause damage to other components, especially rotors, so it is important to replace them before wear reaches that point. Brake pad replacement is one of the most common (and most often botched) auto repairs.
Far too many do-it-yourself mechanics simply replace brake pads with little consideration of the other parts of the system. Auto manufacturers expect brake pad replacement to be part of normal maintenance and generally engineer the calipers to make the chore quick and easy – ideal for the backyard mechanic.
Rotors are subjected to the same friction and temperature extremes as pads. In all but the most exotic cars, rotors are made of metal and are always more wear resistant than the relatively soft brake pad material. Under the heat, friction and pressure of braking, rotors wear out. Under hard braking, the heat generated by friction can make rotors get red hot and become less wear resistant. Foreign materials from the road (sand or dust particles) can become embedded in brake pads and increase the wear on rotors. Rotors will outlast pads but eventually must be replaced along with the pads. Where the backyard mechanic fails is in inspecting the rotor as he replaces the pads. Rotors can be expensive and it is easy to decide to ignore rotor problems.
Depending on the overall condition and amount of actual wear some rotor problems can be corrected by resurfacing. This is less expensive than replacement but is not always the best choice. All rotors are marked with a minimum thickness. Wear or resurfacing that brings the rotor thickness below the minimum makes the rotor susceptible to overheating, warping, cracking or catastrophic failure. Excessive overheating can cause rotors to become brittle or crack. Sometimes, uneven wear can cause parts of the rotor to be below minimum thickness without resurfacing. Do-it-yourself mechanics regularly turn a blind eye to worn rotors to save a few dollars. Professional brake shops have the tools to measure rotors and the experience to recognize other problems that require rotor replacement. No shop wants to let a customer’s vehicle leave with defective rotors. A majority of backyard brake jobs leave rotor problems uncorrected and can jeopardize safety.
Brake Fluid and Hydraulic Components
Government regulations specify the hydraulic fluid used in brake systems. Brake fluid is exposed to a very wide range of temperatures from ambient temperatures far below zero to near one thousand degrees of glowing hot metal under hard braking. One relatively unknown characteristic of brake fluid is its tendency to absorb moisture. The master cylinder has a small reservoir of fluid with a sealed cap to limit exposure to atmosphere. Over time, however, some moisture is inevitably absorbed by the fluid. Owners of older cars need to be aware of problems associated with contaminated fluid and have brake fluid changed at the fist sign of problems. Spongy pedal feel, brake sticking, and brake failure during sub-zero weather are some symptoms. (Moisture in brake fluid can freeze). Brake fluid is clear and colorless. If it is cloudy, brown or has visible contamination it should be replaced throughout the system. This is not a do-it-yourself project.
Any brake inspection or repair should include a visual examination of the brake lines. Metal and rubber brake lines under a car are subject to damage from road debris. Rubber lines can deteriorate with age and develop leaks. A few minutes looking at brake components under a car can prevent dangerous problems on the road.
The master cylinder is the “master” of the system. Master cylinders and the small cylinders in the calipers (often called wheel cylinders) are best left to the professionals. A brake safety inspection can find indications of problems such as leaks but the repairs are best performed by a brake shop.
There are some additional components such as proportioning valves, anti-lock brake systems, warning lights and parking/emergency brakes that are beyond the scope of an article about basics.
Signs You Need to Have Your Brakes Checked
There is very little that can match the panic that follows when a brake pedal goes all the way to the floor without effect on the vehicle speed. Modern vehicles have dual systems that make a complete system failure very unlikely. Proportioning valves and similar devices in the hydraulic system include sensors and switches to detect a severe imbalance of pressure caused by failure of one of the dual systems. If the brake warning light on the dash comes on, carefully get the car to a repair shop, even if the brakes still seem OK.
Many vehicle manufacturers include a brake wear warning device. An annoying, high-pitched squeal every time you apply the brakes is a sure sign of a problem. Jerking or vibration in the steering wheel during braking is a sign of rotor problems. A spongy or slowly descending brake pedal is a sign of possible master cylinder problems. If you find yourself using more foot pressure on the pedal to stop your vehicle you need to get your brakes checked. Under severe braking conditions such as long downhill grades brakes can get so hot that fluid boils or the pads lose their friction properties. When this happens (if you survive) you need to find a place to allow the brakes to cool and, after the trip is complete, have your brakes checked for heat damage or fluid deterioration.
Older vehicles have drum brakes on the rear wheels with a more complex mechanical configuration. Other than the drums and shoes in place of pads and rotors the systems operate the same.
This article was supplied by “WyoKnott” from Constant Content.