Brake discs rotors are vulnerable to damage due to the nature of the function it performs. Disc Rotors are constantly exposed to punishing braking forces and fluctuating operating temperatures. Some common problems are discussed below:-

Corrosion

Since disc rotors are made from cast iron, it is inevitable that rust will set in when exposed to weather conditions. This does not pose any problem for the disc rotors as the rust are clean off during the natural braking process. However in situations where the car is left idle for a period of time, rusting can be so severe that it can damage the disc rotor.

Extreme Temperature Change

In extreme situation where excessive heat is generated during prolong or continuous braking such as descending from hilly terrains, disc rotors may experience warping. Sudden change in temperature causes the disc rotor to expand and contract abnormally. If the overheat disc rotors cools suddenly due to environmental change, brittleness can also set in, causing them to crack and break. Poor quality disc rotors are especially vulnerable to temperature change.

Debris

Dirt and debris can be lodged onto the brake pads. When this happens, the surface in contact with the debris causes the disc rotors to score. Scoring are deep grooves or cuts in the disc rotors that weakens the strength of the disc rotors. Noise is another problem of trapped debris. Brake pads that have poor quality control are prone to cause this problem as foreign contaminants are introduced into the manufacturing process during the baking of the friction cake.

Worn out brake pads

Disc rotors can also be damaged by brake pads that have been worn off to expose the backing plate. Instead of the friction material, the backing plate is rubbing on the surface of the disc rotors. This potentially scores the disc rotors as well. It is therefore the responsibility of the driver to monitor and change worn out brake pads during regular servicing.

A number of factors affect the useful lifespan of brake pads. While brake pads are generally designed to take extensive braking force and heat, they are worn off with extended usage over time. Although most car manufacturer claim that the original brake pads can last for more than 50,000km, there is no one standard number that can be guaranteed as there are various factors affecting the lifespan of the brake pads.

Friction Material Composition

In general, there are 3 types of friction materials used in brake pads; organic, semi-metallic and ceramic. Organic brake pads are generally quieter and are gentler on the brake disc rotors. Semi-metallic brake pads are able to withstand higher temperature range but can cause more wear on the brake disc rotors. Ceramic brake pads on the other hand have usually a longer lifespan but there could be a potential noise issue.

Friction Material Formulation

Within each friction material composition, there are different raw materials added to form the ‘cake’. The proportions of raw materials, coupled with the right combination of time, heat and pressure affects the performance as well as the wear rate of the friction material.

Driving Style

For the heavy footed who prefers to stop at the last possible minute or frequently stopping at high speed, brake pads will be worn off much faster. Gradual stopping with anticipation will help to extend the usage of brake pads

Driving Environment

In driving conditions where there are many stops and turns, the increase in frequency of stepping on the foot pedal is inevitable. The increase wear on brake pads is compounded with driving in hilly terrain. Except for driving style, many factors are not within the drivers’ control. However the driver can choose to use a reputable brand that has the proven formulation to suit their driving demands.

Brake master cylinders holds the brake fluid in a reservoir and is the component in the car that re-distributes the converted hydraulic forces from the brake pedal to the brake calipers and brake wheel cylinders through the brake hoses.

In general, there are 2 ways to tell if the brake master cylinder is failing.

One of the first tell-tale sign of a failing brake master is the ‘spongy’ feeling when the brake pedal is stepped on. When the brake pedal has to be depressed further than usual, air could have entered into the brake system through leaks in the cylinder chambers. If the brake pedal depresses on its own, it is also a hint of a possible leak in the brake master cylinder as it is an indication of pressure loss.

It is normal to see the fluctuation in the brake fluid level in the reservoir of the brake master cylinder when the brake pedal is depress. If it doesn’t, the seal may be damage. It is also nothing unusual if the brake fluid level drop as the brakes wear over time. Likewise, if this is not happening, there could be a leak somewhere.

In cases where leakage is external, it is possible to conduct a visual inspection to identify the leaks. External leaks usually occur at the mount between the container and the cylinder or at the threaded area.

Brake noise can be very disturbing. It is a common complain faced by drivers when they bring their cars into the service workshop. Understandably, drivers tend to view brake noise as a problem with the brake system, and brake pads are typically thought to be the blame for the noise. Brake noise happens when there are excessive vibrations in the brake system. Depending on the type of brake noise, some can be due to vibrations occurring with the other components in the brake systems. Not all brake noise is due to a problem with the brake pad itself.

Brake Squeal

Brake squeal is the most common complain amongst the different possible brake noise. There can be numerous causes for brake squeal. If brake squeal occurs immediately after replacing the brake pads, it is likely due to bedding-in issue, which may just go away after continuing to drive for a while longer. To reduce likelihood of brake squeal due to bedding-in, it is a good practice to skim and clean the surface of the disc rotors during replacement of new brake pads to ensure proper fitment between the surface of the brake pads and the disc rotors. Brake squeal that occurs immediately after replacement of new set of brake pads can also be due to incorrect assembly by the mechanics. More often than not, the use of anti-noise dampers such as shims will solve the brake squeal problem.

Brake squeal can also happen when the movement of the piston in the caliper is restricted. This causes inconsistent pressure to be applied onto the brake pads. If the caliper seal and piston is not damaged, using brake cleaner to clean and lubricate the caliper should improve the noise problem. Otherwise the caliper kit may have to be replaced.

Many brakes squeal occasionally, but if the squeal is consistently present, it could be a due to glazing. Glazing is a condition caused by crystallization of the friction material on the brake pads as a result of being overheated because of abusive use. If the brake pads are glazed, there will be drop in stopping performance. This condition can usually be arrested by using sandpaper to sand off the crystallization on the brake pads and the disc rotors.

Brake Judder

Brake Judder occurs as low and deep noises. They are not due to problems with the brake pads but are rather cause by the disc rotors. When existing disc rotors are used with new set of brake pads, there could already be some damages on the disc rotors. It is likely that the disc rotors have poor tolerances which arise from poor fitment on the hub. This causes the disc rotors to wear unevenly, thus resulting in huge disc thickness variation. In serious cases, vibrations can be felt on the steering wheel. To resolve brake judder, it is advisable to replace the disc rotors.

Brake Grinding

For those cars that have wear sensors, it is likely the brake pads are changed whenever the warning light is on. But for those that do not, it is not uncommon that the wear on the brake pads tends to be overlook. Grinding sound happens because the friction material on the brake pads are worn off, exposing the backing plate to the surface of the disc rotors. This is certainly a cause of concern and should be address immediately as there is a huge potential of braking failure.

For optimal performance of any brake system, brake pads and brake disc rotors have to be compatible with one another. Brake pad bedding-in facilitates the fitment of contact surfaces between the brake pads and the disc rotors. During the bedding in process, a layer of the friction material on the brake pad is evenly deposited on the contact surface of the disc rotor. Under normal operating temperature, the heat generated in the brake system allows for the formation of a transfer layer. After continuous usage over a period of time, the entire face of the disc rotor is evenly covered with the friction material of the brake pad.

The key to braking without excessive noise is the transfer layer on the disc rotor has to be evenly distributed. Uneven deposits on the disc rotors cause brakes to vibrate excessively. But before the layer can be evenly distributed, there is an inherent period of time initially where the deposits are still sparsely and uneven distributed. This is the reason why mechanics advise drivers to be gentler on the brakes before brakes pad are bed-in. It is also why drivers should not be too keen to draw into conclusions that the performance of the brake pads is questionable during the initial bedding-in period.