Symptoms of malfunctions when inspecting the braking system

Uneven wear of brake pads or discs

• Jamming of brake caliper or cylinders, faulty parking brake
• Broken wires of wear sensors of brake shoes
• Squeaks, noises and vibrations during the operation of the brake system
• Leak or low level of brake fluid

Inspection of the braking system is recommended at least twice a year. It is reasonable to combine the test with the seasonal change of wheels, when the brakes are available for inspection. It is worth to immediately unscheduled to contact the service, if during the braking car leads to the side or there are extraneous noise, vibration.

When checking the brake system after removing the wheels and inspecting, there may be certain signs of defects that require more detailed attention in the car workshop.

1. Uneven brake pad wear

One of the possible causes of uneven wear of the disc pads is their incorrect installation. In this case, you need to check the direction - on some pads there are marks "left", "right" or arrows in the direction of rotation of the wheel. In addition, if only one pad of the pair is worn out, or the pair has a wedge-shaped wear, then the brake system elements probably do not work properly (more on this below). In the case of extreme wear of the pads - up to a thickness of lining 3 millimeters or less, - an acoustic indicator of wear may emit a noise or the lamp on the instrument panel may ignite, warning the driver to replace the pads.  If you do not control the condition of the brake system, sooner or later there will be a squeak, a squeaking or a rattle - the friction work pad will be erased, and the metal substrate of the pad will begin to rub against the metal surface of the disc. In this situation, in order not to be failed  the brake disc, caliper or other elements of the brake system, it is necessary to immediately call the car service.

In the drum brake system, the pads also need to be changed as the minimum permissible thickness of the friction, determined by the automaker, is reached. Uneven wear of the pads on the left and on the right indicates that there are problems in the system. For a detailed inspection of the mechanisms, the drum must be removed. In some systems, the initial working position of the shoes is determined by an automatic tensioner. In this case it is important to make sure of its operability and mobility of all mechanisms.

When replacing the drum blocks, it is recommended to use ready-made spare parts for the drum brake system, such as Bosch Kit Pro and Kit Super Pro.

2.Uneven wear of the brake disc and drum 

Scraps, scuffing on the surface of the brake disc may be the result of extreme wear of the pads or dirt particles. If the car owner did not change the pads in time, in this case, after erasing the frictional surface, the metal backing of the lining becomes the working surface during braking and rubs against the disc or drum. All this leads to their deformation and uneven wear.

When replacing the disk pads, it is necessary to measure the residual thickness of the disk at several points. Indirectly, about the wear can say the ledge on the working surface of the disc along the edge of the brake shoe. If the disc is worn unevenly or its thickness is small, then with frequent intense braking its plane due to heating can "lead", which will lead to the occurrence of vibrations. In addition, if the driver noticed a blue color on the discs, this indicates that it was overheated and it is necessary to contact the car service for more detailed inspection. Such a disk could change its properties, geometry, deform, on its working surface, cracks could appear. As a result, the braking distance is prolonged, noise, beating, reliability of the brake system components is reduced. To prevent this, damaged discs must be replaced.

In the drum brake system, furrows or scuffing can also occur. In addition, when the friction portion of the brake shoe is abraded, the wear of the drum is accelerated. The brake drum must be replaced if the residual thickness of its working part has reached the minimum permissible level determined by the car manufacturer. Or if the drum received mechanical damage. An important recommendation affecting safety is the simultaneous replacement of all pads or drums located on one axis.

3․Corrosion and malfunction of components, wedging of brake caliper or cylinders, lack of lubrication on guides of caliper, faulty parking brake

Corrosion and impairment of the components of the brake system can block the movement of the pads and lead to uneven wear, noise, vibration and even wedging of the caliper (disc system), the souring of the "pad-drum" pair or the brake cylinder (drum braking system).

When inspecting the support, it is necessary to clean all components from the dirt and check the lubrication on the guide bolts and the movement points of the shoe. The use of a lubricant, such as the Bosch Superfit, is an important point in the brake servicing regulations. Its absence leads to premature wear of the components.

In the drum brake system, it is likewise worthwhile to clean all components of dirt and dust and make sure that there are lubricants on the mechanisms or points of movement of the brake shoes. For corrosion on springs and other elements of the system, they must be replaced with new ones. Otherwise, the spring may break or permanently lose its properties, which can lead to accelerated wear or jamming of the "brake pad-drum" pair.

When checking the brake system, it is also necessary to check that the parking brake is functioning properly.  Due to a violation of its performance, the main brake system may also suffer - the efficiency of the rear mechanisms decreases. Thus, a common fault is the tension of the cables, their corrosion and impairment.

4. Torn wires of brake pads wear sensors 

Probably, the pads with torn wires of the wear sensors are mixed up during installation.  Or the breakage occurred as a result of mechanical damage during operation, for example, off-road.  In such cases, the warning light on the instrument panel lights up, or, conversely, even when the wear sensor is activated, the driver will not see a warning light indicating the replacement of the brake shoes. The latter can lead to extreme wear on the disc and pads and disable other elements of the brake system. To prevent this from happening, pads with damaged wires or wear sensors must be replaced with a new set.

5. Leak or low level of brake fluid; wet boiling point

When inspecting the brake system, you should pay attention to the level of the brake fluid in the tank. A decrease in the level indicates a large wear of the pads and discs or drums, or the leakage of the hydraulic system.

According to the regulations, the brake fluid must be changed every 2 years.  But during the inspection it is necessary to check it with a special tester, such as the Bosch BFT 100.  Only measuring the boiling point can give true information about the state of the brake fluid. If a certain wet boiling point is below the minimum allowable value, the brake fluid must be replaced with a new one.

6. Squeak and noise, vibration after installing new pads

The driver complains of squeaks, but the pads have already changed, and when examined they have a good condition. Hence, it is worth checking the adjacent components of the suspension and steering. Separately, the components of the system may not be noisy. But when in different places accumulated wear gradually begin to vibrate and come into resonance at once several details - the braking system starts to "sound" in full force.​It can be pads, a disk, traction, silent blocks, stabilizer racks and even a shock absorber. Therefore, when noise occurs, inspection of all adjacent components is necessary. Changing pads, disks or other elements of the system is necessary only after checking the entire brake mechanism and identifying all the defects, the causes of noise. 

Source: www.bosch-automotive.com