Brake System Information

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Brake System



Vehicles of today offer a wide spectrum of braking systems. There are four-wheel disc brake systems made from ceramics, composite materials and cast iron. Many of today's cars and light trucks feature a computer controlled braking system referred to as ABS, which is an acronym for Anti-Lock Braking System. This system helps drivers maintain a higher level of control in emergency or extreme driving situations by pulsing the disc brakes on and off, thus avoiding skidding while providing maximum brake efficiency.
In addition to four-wheel disc brakes there are also many systems that combine front disc brakes with drum brakes in the rear. Each system has its merits and pitfalls.

In the most general terms the illustration to the right shows the basic brake components found on many of today's passenger cars and light trucks.

In such an arrangement the front disc brakes do 60% to 70% of the work in slowing your car when the brakes are applied.

Disc brakes, as the illustration to the right shows and the name implies, are built around a large set of parallel discs called rotors. Most of these have air fins between them to help dissipate the heat caused by the friction of the brake pads. The caliper assembly holds a pair of brake pads on either side of the rotor. When the brake pedal is depressed, brake fluid is forced out of a master cylinder and through brake lines to the calipers. Within each caliper, hydraulic pressure is applied to a piston that in turn presses the brake pads against the rotor. The friction between the pads and the rotor slows the car.

By comparison to your front brakes, the rear brakes do relatively little work in stopping your car. Given the lighter requirements (in most vehicles 60% of the stopping is handled by the front brakes, 40% by the rear) some vehicles have drum style brakes on the rear. This style of brake is similar to disc brakes, although nowhere near as effective. They have "shoes" rather than brake pads and rather than clamping down on a disc, they press outward against the inside surface of the brake drum.

Often rear drum brakes also function as the car's parking brake, which is activated through a cable that is either attached to a pull handle or parking brake pedal with release.

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Disc Brake Problems





Disc brake problems can usually be divided into two categories: vibration and noise.
If you suspect a brake problem may exist, road test your car and listen for any noises. Note any brake pedal vibration or vehicle pulling when applying the brakes.


Noises typically indicate brake pad problems;

pedal vibration suggests rotor related problems;
pulling is usually caused by a faulty caliper.


Though there are many clues to what your brake problem may be, it is virtually impossible to determine what repairs are actually needed until the brake assemblies are inspected by a qualified technician. A preliminary road test is only one step in helping to pinpoint potential problems.


To solve these problems, there are three main categories of disc brake service: pad replacement, caliper overhaul, and rotor machining or replacement.


Lateral Runout
Lateral runout is side-to-side motion in the rotor as it turns on the hub. This erratic motion in turn causes uneven wear in the rotor. As you drive, even without the brakes applied, the rotor hits the pads lightly on each revolution. This extra wear leaves a thin spot on the rotor. Once this thickness variation is worn into the rotor, the brake pedal will vibrate when braking.

Lateral runout is most often the result of small inconsistencies in the rotor and vehicle hub that, when combined, are often magnified. Runout can also be induced by uneven wheel torque (lug nuts should always be tightened to correct torque), improperly adjusted or worn wheel bearings, corrosion, or damage from hitting a curb or pothole. Any of these conditions can easily lead to poor brake performance that will worsen over time.

Disc Dishing
Dishing is a condition when the rotor becomes dished and is no longer square to the hub of the car. It invariably leads to poor braking performance because the brake pads have difficulty making full contact with the friction area of the rotor. This in turn causes parts of the rotor to become hot, warp and wear unevenly.


Lining Material Transfer
This is a common occurrence where very small amounts of brake pad material transfer and adhere to the rotor. A problem develops when uneven amounts collect to create an uneven friction surface on the rotor. This makes the brake pads "grab" which in turn is felt as a pulsation.
Brake Vibrations
Many vehicles today are equipped with Anti-lock Braking Systems (ABS). During emergency stopping situations, ABS provides a rapid series of brake applications that allow the driver better control of the vehicle. Drivers who are not familiar with ABS, may easily confuse this pulsing sensation with abnormal brake system vibration.

Abnormal brake vibration, called pulsation or roughness, is sometimes the result of wheel problems. Before examining the brake system it is important to eliminate wheel conditions that might lead to uneven braking. Specifically, worn bearings, uneven wheel torque, or improper wheel balance will have negative impacts on brake performance. It is important to ensure that these conditions have been addressed before tearing into the brakes.

If the problem is with the brake system, the vibration is most likely a result of thickness variation in the rotor. As pads squeeze a rotor that is not of uniform thickness, their effectiveness fluctuates — grabbing the thick spots and slipping over the thin. This in turn is felt as a pulsation in the pedal.


Solution
Dishing and lateral runout can be corrected by machining (cutting) the rotor. We recommend a machining process that is done with a brake lathe.

The computer guided on-car lathe is bolted to the hub of your car. It then makes a series of adjustments to align the lathe axis with the hub axis.

The cutting head of the lathe then refinishes the brake rotor until it is smooth and precisely matched to the individual axle hub.

The on-car lathe method yields brakes that operate more smoothly, than new or replacement rotors.

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Disc Brake Noises
Today's higher technology vehicles have complicated braking systems. Further, given environmental and safety concerns. automakers have been forced to abandon asbestos brake pads and rely instead on organic, low metal and semi-metallic brake lining materials. These composite materials, in normal use, may emit an intermittent squeal or groan noise when the brakes are applied. These normal sounds are typically heard during the first few brake applications in the morning. They may also be brought on by environmental conditions such as cold, heat, moisture, road dust, salt or mud. Remember, occasional brake noise is normal and does not indicate a performance problem.

The word of caution is occasional — if the sound or condition becomes a regular occurrence,then it must be addressed.

Problems with disc brakes can generate a number of noises as the brakes are applied; most are the result of friction material problems. Following are some typical sounds and their related causes.

Scraping or grinding sounds indicate that brake linings (pads) have been worn down to the backing plate leaving metal-to-metal contact between the pad backing plate and the rotor.

Squeaks and squeals that occur when the brakes are applied are often the result of problems with the lining friction material that are worn, damaged, or missing vibration damping components.

Light scraping or chirping may be the result of a pad wear indicator rubbing against the rotor. Some pads have a small metallic piece that will rub the rotor as the pad wears too thin. If this sound is ignored, pads will continue to wear to the point of damaging the rotor.

Louder scraping noises may be the result of a bent splashguard rubbing against a rotor.

Remember these are only clues to your brake problem.