Knock when braking: possible causes, troubleshooting and recommendations

2024 Author: Erin Ralphs | [email protected]. Last modified: 2024-02-19 11:42

On numerous thematic forums, motorists complain that from time to time they hear uncharacteristic sounds and vibrations when braking. This knock occurs in various situations. We will analyze the causes of this unpleasant phenomenon, and also learn how to troubleshoot.

Brake systems

This is one of the key security factors. It is with the help of the brakes that the driver can reduce the speed of the car up to a complete stop. There are several types of systems. The most common option is hydraulically driven. Here, the force from pressing the pedal is transmitted with the help of brake fluid to the actuators. They are on the hubs. As for the brake mechanisms themselves, two types of solutions are used in cars. These are disc brakes popular today and an older version - drum brakes. In the first mechanisms, the pads interact with a disc mounted on the hub. As for the latter, they are inside the brake drum. The deceleration process is carried out due to the fact that the pads are unclenched and pressed against the internalplanes of the drum.

Drum brakes are quite an old and archaic solution. But on budget cars they are still widely used. A parking brake is also implemented by means of drum brakes. Thus, there are disk systems in front, and drum systems in the back.

About Service

Like any other system in a car, the brakes need regular maintenance. In the case of a hydraulic mechanism, it is necessary to periodically replace the pads - they tend to wear out. It is important to monitor the condition of both discs and pads from time to time. Drum brakes should also be checked regularly. As for the drive itself, here they check the condition of the lines, visually diagnose the system for fluid leaks, and control its level in the reservoir.

Also, after any maintenance work on the car's brake system, it is necessary to bleed. This is done in order to remove air from the lines. The presence of air in the pipeline can reduce the effectiveness of the brakes, or even affect their performance. Since the system does not have a large number of different components, many consider it unusually reliable and think that with proper care it will not cause any serious problems to the owner. However, this is not always the case. Problems can arise in structures of any complexity. One of the most common problems withbrakes - these are characteristic sounds when braking. Knock appears when you press the pedal.

Features

These sounds can have a very different character. They can be distributed from different sides of the car, they also occur in a certain position of the pedal. Knocking can be either single or repetitive. Most often, when braking, a knock is heard from the front after any maintenance work on the brake system. It is very difficult to diagnose problems in the brake mechanisms by knocking. Even if something vibrates, it is not at all necessary that it will be a braking system. Sounds can be produced by leaking struts and failed rear shock absorbers, anti-roll bar fasteners and many other components.

On the difficulties of diagnosis

In addition to the brake system, it is worth checking for malfunctions in the wheel drives - this is evidenced by a knock in the front suspension when braking. This is a fairly common occurrence faced by motorists. Experts say that even the steering system and engine mounts can often be the culprit for suspicious sounds. That is why fault diagnosis is a very complex process. One of the typical features of the appearance of sounds during braking is that the knock appears only in the pedal, which is squeezed out halfway. If you squeeze it to the floor during intensive braking, then extraneous sounds will disappear. Often, car owners write on forums that this sound can be heard when driving at low speeds, also at medium speeds. On high - less often. Most of the time you can't hear anything.as long as the brake mechanism is cold.

Another point that complicates the diagnosis is the frequency with which there is a knock when braking in the front or rear wheel. It can be heard for some time, then disappear completely and reappear after a while. Now many cars are equipped with ABS - sometimes the malfunction may lie precisely in it. But this is far from a fact. Even self-diagnosis systems are unable to find errors in the operation of the anti-lock system.

Typical Causes of Brake Knocking

Consider the typical causes of knocks and other extraneous sounds. In fact, there are few such reasons. You can fix them yourself.

Caliper guide play

One of the most popular causes of knocking is worn seats for mounting caliper guides in the brake mechanism. In this case, the caliper has play, which causes vibration during braking. Knocking is also often manifested. Solving this problem is very simple - it will completely disappear after replacing the guides.

Wedging the caliper piston

During braking, fluid presses on the piston. However, it gets stuck in the cylinder and stays in that position until the increase in pressure pushes the piston out of it. When this happens, it hits the pads with force and presses them down - this is the reason why there is a knock from the front when braking.

To correct this situation and get rid of annoying sounds, just remove the caliper and remove the piston. Then visually check its condition, and together with the piston inspect the surface of the cylinder. If signs of corrosion are found during the inspection, the cylinder must be cleaned and the piston is recommended to be replaced.

Brake disc

Often, knocking when braking in the front wheel occurs due to curved discs. This occurs in case of overheating. During braking, the pads, passing through a place where there is a bend, beat against it, which causes a knock.

This problem is treated, but it is quite difficult to accurately identify abnormalities without special equipment. With strong defects, of course, everything is visible visually, but then it is better to replace the disk with a new one. You can also grind the surface of the disk on a lathe or with the help of special tools. It is better to replace the pads, otherwise, after restoring the disk, they will again make production on it. Sometimes the curvature of the disc can be guessed by the condition of the pads. Their wear will be uneven.

Knocks in drum systems

In such mechanisms there are a sufficient number of places where a knock can occur from behind when braking. Often this mechanism is a parking brake. Since the parking brake cable diverges under the car into two parts, it may well be that one of the parts has relaxed. The mechanism is weak, and when the driver presses the main brake pedal, the pads of the drum system diverge. Betweenpads and parking brake thrust bar create play, which is the cause of the knock.

The distribution part also often knocks. If at least one of the cables is not tight enough, then the bar will vibrate and the driver will hear a knock when braking in the rear wheel. Another reason is the pad retainer. If he leaves his seat, the block will move - this will provoke a blow to the drum. Rarely, a loose rear hub bearing can cause vibration. But most of the time it's just noise. It shows up at low speeds when braking. Also a fairly rare reason is long wheel bolts. Longer - catches in the process of braking. The problem is solved in an elementary way - by replacing the bolt with a short one.

In models built on the popular B0 platform, the rear mechanisms begin to creak during operation. The reason is banal - the brake pad rubs against the shield. It is easy to diagnose - remove the latch, then remove the block. Damage will be visible to the naked eye. Treating this situation is also very simple - the damaged area should be cleaned and greased with grease. And then the sounds will disappear.

Brake noise with ABS

On vehicles equipped with ABS, you can easily check if it is the cause of the knock. To do this, pull out the fuse, which is designed to operate the system. In this case, the system will stop working, but the brakes will function. If there is a knock from the front when brakingor disappeared from behind, then ABS is to blame.

Pendant and other items

The pendant is the next item to check carefully. It often happens that the problem was not hiding at all in the brake mechanisms. Various suspension parts may well make knocks and other unpleasant sounds for the driver.

Silent blocks and bushings

These parts with a lot of wear may cause a characteristic sound. If the silent block in the steering mechanism is worn out, then it will knock. Finally, it is recommended to check the engine mounts and their mountings. Just a small indulgence is enough for everything to go “shaking” in the cabin.

CV joint

If a knock is clearly heard when starting and braking, then the first step is to diagnose the CV joints. Pay attention to the sounds when turning the wheels for the first time. If knocks are heard, then the problem is in the chassis of the car. Also, among the reasons, one can single out a broken constant velocity joint, a failed tie rod, and a worn rack. By the way, the latter can leak in the event of a malfunction - you should pay attention to the anthers. Perhaps they are out of order. Also, vibrations may indicate that it is soon necessary to replace the ball joints and shock absorber struts.

CV

The brake system is the basis of driving safety. If the slightest malfunction occurs in its operation, it is necessary to immediately look for a malfunction and fix the problem. In fact, there are not so many reasons. In addition, everything can be much simpler - for example, a knock on the wheel whenbraking occurs due to the unscrewed caliper mounting bolt.