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Signs of malfunctions of brake system from Bosch specialists.


The brake system should be reviewed at least twice a year. The test should be combined with a seasonal change of wheels when the brakes are available for inspection. It is worth noting immediately to the service if, when braking, the car leads to the side or there are extraneous noises, vibrations.
During the check of the braking system after removing the wheels and inspecting, there may be certain signs of defects that require additional attention in the car workshop.
1. Uneven shoe wear
One of the possible causes of uneven wear of the disc pads is their improper installation. In this case, it is necessary to check the direction - on some blocks there are marks "left" / "right" or arrows in the direction of rotation of the wheel. In addition, if there is only one shoe worn with a pair, or the pair has wedge-shaped wear, then the support elements probably do not work properly (more on this below). In the case of extreme wear of the pads - up to a thickness of the lining 3 mm or less - the acoustic wear indicator may be noisy or the bulb on the dash panel may turn on, warn 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, the brake disc, caliper or other elements of the brake system do not fail, it is necessary to immediately call the car service.
In the drum brake system, the pads also need to be changed in the event that the minimum permissible clutch thickness specified 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 thorough 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, which includes all the necessary replacement parts, including springs and cylinders. Distinctive characteristics of sets Kit Super Pro - the regulator of a backlash in the complete set. In addition, they are delivered fully pre-assembled, which significantly reduces the time to replace components and reduces the likelihood of errors during assembly.
2. Uneven wear of the brake disc or drum
Furrows, burrs on the surface of the brake disc may be the result of the extreme wear condition of the shoes or dirt particles. If the car owner did not replace the pads in time, in this case, after erasing the friction surface, the metal pad substrate becomes the working surface during braking and experiences friction from 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. About wear can indirectly speak performance on the working surface of the disc along the edge of the 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 bluish 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, fretting, and reliability of the brake system components are reduced. To prevent this, damaged discs must be replaced.
In the drum brake system, furrows or burrs may also appear. In addition, when you erase the friction part of the pad, drum wear 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 mobility impairment of components, wedging of brake caliper or cylinders, 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, noises, vibration and even seizure of the caliper (disc system), souring of the "drum-drum" pair or the brake cylinder (drum brake 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, for example, Bosch Superfit - is an important point in the maintenance regulations for the braking system. Its absence leads to premature wear of the components. Some manufacturers do not provide lubricant on the guides, but in most cars it is mandatory. Therefore, when servicing the braking system, the instructions of the car manufacturers must be observed.
In the drum brake system, it is likewise necessary to clean all components of dirt and dust and make sure that there is oil on the mechanisms or where the pads move. In case of 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 "shoe-drum" pair.
During the check of the braking system, it must also be ensured that the parking brakes are 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. It is possible that it will be sufficient to regulate them properly. But problems in the operation of the parking brake may indicate corrosion and sagging of the cables or a disruption in the mobility of the rear brakes and associated mechanisms. In this case, it is worthwhile to carefully check the operation of all components and, if necessary, replace them with new ones.
4. Broken wires of wear sensors of shoes
Most likely, the pads with broken wires of the wear sensors have been misinterpreted 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 if the wear sensor is triggered, the driver will not see a warning light indicating the replacement of the 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. Leaking or low level of brake fluid
When inspecting the brake system, you should pay attention to the level of brake fluid in the reservoir. A decrease in the level indicates a significant wear of the pads and discs or drums for leaks in the hydraulic system.
According to the regulations, the brake fluid must be replaced every 2 years. However, when inspecting it is necessary to check it with a special tester, such as Bosch BFT 100 Only measuring the boiling point can give true information about the state of the brake fluid. If the specified boiling point is below the minimum allowable value, the brake fluid must be replaced with a new one. Information on what type of system is used in the system can be found in the vehicle\'s operating instructions. Or you can use Bosch ENV6 brake fluids that are compatible with all DOT types on a polyglycol basis.
6. Squeak and noise, vibration after installing new shoes
The driver complains about the creaking, but the pad has already been changed, and at the time of inspection they are in good condition. Then 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 begins 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, it is necessary to review all adjacent components. 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. For example, noise may cause the nuts on wheels to be tightened without a torque wrench. As a result of tug-of-war "drive" the disc, you will be beaten. If you put a new part on a faulty mechanism, it will not work well. Moreover, if you put the same shoe on different cars, on one it can behave perfectly, and on the other - to resonate with other details.