The appearance of extraneous sounds in the chassis or brake system always causes alarm to the owner of the car. Especially frightening is a deaf knock during braking, which may indicate both a slight wear of components and a critical malfunction that threatens an accident. Ignoring this symptom often leads to the destruction of adjacent suspension units and an increase in the cost of repair several times.
The nature of the sound can range from a light tapping to powerful blows, giving to the steering wheel or body. Brake system It is under enormous pressure, and any backlash part begins to emit warning signals. In this article, we will discuss in detail the mechanics of knocking, methods of their localization and ways to eliminate faults.
Timely response to changes in the acoustic background of the car allows you to save not only the budget, but also life. Diagnostics It must be done in a complex way, as sound can spread over metallic elements, deceptively pointing to one detail while the problem lies in another.
Mechanics of knocking in the brake system
To understand the nature of sound, it is necessary to consider the physics of the braking process. At the time of pressing the pedal, the brake pads are pressed against the disc with great force, stopping the rotation of the wheel. If there is a free-range (backlash) in the system, the kinetic energy causes the metal surfaces to hit each other.
Often the source of the problem is not the shoe itself, but its seat. The guide calipers can wear out, forming gaps. At this moment brake-up It starts to “walk” relative to the bracket, emitting a characteristic deaf sound during each compression and compression cycle.
For primary diagnosis, you can gently shake the wheel with your hands when the car is raised (subject to safety precautions) and at the same time ask the assistant to press the brake. If the knocking disappeared when the pedal was pressed, the problem is in the caliper or pads.
Another factor is the condition of the brake discs themselves. If a work surface has formed a production or "step", the pad may fit loosely or unevenly. This causes vibrations that are perceived by ear as thumping or rattling, especially at low speeds.
Diagnosis of brake calipers and pads
The most common cause of knocking is wear of elements of the brake mechanism. During operation, the pads become thinner, and the stroke of the caliper piston increases. If you do not monitor the thickness of the friction material, the piston can skew, which will lead to knocks.
Particular attention should be paid to the guide fingers of the caliper. They should slide freely in lubrication, but not have excessive backlash. Time-washed lubrication or damaged anther leads to corrosion and jamming, which causes uneven wear and tear. brake-noise.
- 🔍 Visually inspect the anther guides for breaks and cracks.
- 🔧 Check the movement of the caliper finger – it should move from the hand’s effort, but not hang around.
- 💰 Evaluate the residual thickness of the brake pads (critical minimum is usually 2-3 mm).
- 🔩 Check the presence of anti-script plates and their fixation.
⚠️ Note: If you find that one of the calipers warms much stronger than the others after the trip, this is a sign of souring. Operation of the car with a jammed caliper can lead to fire or complete failure of the brakes on the wheel.
Sometimes knocking occurs due to the banal lack of lubrication on the back of the pads or on the ears with which they are attached to the brace. Metal ringing or thud in this case is eliminated by applying a special high-temperature lubricant. The use of graphite lubricant or lithole is unacceptable here, since they cannot withstand temperature loads.
The effect of suspension on the nature of sound during braking
The noise source is not always directly in the brake assembly. Often a deaf knock during braking provoke elements suspensionThose who are under heavy pressure at the time of the body. Inertia causes the car to shift forward, loading the front levers and shock absorbers.
The first suspects are often Silentblocks. Rubber metal hinges eventually dry up and crack. When braking, the lever shifts in the broken Silentblock, issuing a deaf, blow. Similarly, worn bushings of the transverse stability stabilizer behave.
Diagnosing suspension is more difficult, as knocking can be periodic. It is necessary to rock the car on the lift or observation pit, using the mounting blade to create a load on the levers. Luft in ball supports can also give a knock, although more often it manifests itself on the irregularities of the road, and not only when braking.
Brake discs: beat and deformation
The condition of the brake discs directly affects acoustic comfort. Overheating of the disc (for example, after active driving and getting into a puddle) causes its curvature, known as "eight". When rotating, such a disc hits the pads, causing a pulsation of the pedal and a characteristic knock or hum.
The minimum thickness of the disk is a critical parameter. If the disc is drained below the permissible limit, it becomes less rigid and can deform even from standard braking. In this case, a mandatory replacement is required, since the duct will no longer restore the necessary characteristics.
| Type of disc failure | Symptoms | Method of decision |
|---|---|---|
| Thermal deformation | Pedal beat, steering pulsate | Dripping or replacement |
| Critical wear and tear | Whistling, reduced efficiency | Only a replacement. |
| Corrosion of the working surface | Roughness, jerking. | Laundry or replacement |
| Cracks | Strong knock, risk of destruction | Urgent replacement |
It is important to check the disks for beat using the clock type indicator. The permissible values usually do not exceed 0.05 mm. Exceeding this parameter will feel like a vibration to the driver. Brake discs It is always recommended to change the pair on the axles to ensure uniform braking.
Hidden causes: steering and bodywork
Sometimes a deaf knock during braking masquerades as a brake problem, but comes from the steering mechanism. The luxe in the rail or worn tips of the steering rods can give themselves out exactly at the moment of braking, when the wheels are experiencing a longitudinal load.
It is also worth checking the attachment of the calipers themselves to the turning fist. The weakening of the mounting bolts is a direct threat to security. The vibrations gradually unwind the fastener if it was not fixed by the carving fixer or not stretched with the right moment.
Rare causes of knocking
In rare cases, knocking can cause the friction lining to detach from the metal base of the pad. Also, the cause may be a crack in the brake caliper itself, which occurs on cars with high mileage or after strong blows on the curb.
Don’t forget about the body and protection. Weakened protection of the crankcase or under-arm can be shifted during braking and hit the levers or shock absorbers, creating the illusion of a serious breakdown in the braking system.
Algorithm for troubleshooting and troubleshooting
Effective repairs need to be done consistently. Chaotic replacement of parts at random will only empty the wallet. Start with visual inspection and simple manipulations, gradually moving on to complex diagnostics.
☑️ Checklist for knock diagnostics
If external diagnostics did not give results, you will need to dismantle the wheel and a deeper revision of the nodes. When assembling, use a dynamometer key. The moment of tightening of the caliper and wheel bolts must strictly comply with the manufacturer's specification.
⚠️ Warning: After replacing any brake system components, be sure to pump the system to remove air. The presence of air in the circuit makes braking inefficient and dangerous, and can also cause additional noise.
Remember that brake He doesn't tolerate compromise. If you are not confident in your abilities or you do not have the necessary tool, it is better to contact a specialized service. Savings on qualified brake repairs are unacceptable.
The main cause of thud knocking during braking in 80% of cases is the development of guide calipers or wear of the Silentblocks of the front levers.
Frequently Asked Questions (FAQ)
Can I drive if I hear a knock when braking?
The operation of the car is possible only in the "before service" mode and at low speed. If the knock is strong, accompanied by a pedal beating or an increase in the braking distance, the movement should be stopped and a tow truck should be called.
Why does it only knock with cold brakes?
This may indicate increased gaps in the mechanisms that are selected during thermal expansion of parts. It is also possible to use low-quality shoes that "blown" in the cold.
Do I need to change the brake discs along with the pads?
It is advisable to change the discs and pads at the same time. Older discs have a production under the old pads, and new pads will last longer, perhaps making noise.
How often should the calipers be lubricated?
It is recommended to maintain (cleaning and lubrication) guide calipers with every second replacement of brake pads, approximately once every 30-40 thousand kilometers.