Brake disc heating temperature. The front brake disc gets hot: possible causes, troubleshooting and reviews
Normally working, serviceable brakes are like a fire extinguisher. We don't notice them and don't remember them. Then, suddenly, God forbid, an emergency occurs or emergency braking is required, and with surprise, turning into panic, we realize that the car has faulty brakes.
High temperature is normal brake disc operation.
Therefore, in order not to face the fact of an accident in all its glory, it is necessary to systematically independently diagnose the brake system: compliance of the brake pads with the manufacturer’s requirements and the thickness of the brake discs.
There are many factors leading to a malfunction of the brake system, or rather its individual elements. Let's pay attention to overheating of the brake discs.
So that you understand what we mean we're talking about. High demands are placed on the material of the brake disc, and first of all, these are strength, high coefficient of friction and stable characteristics when heated, high thermal conductivity, resistance to sudden thermal shock, and low adhesion ability.
Yes, it's all about him - about the brake disc of a production car. After all, its operating temperature reaches 200-300 degrees C. Therefore, the main material for brake discs of a production car is: steel or cast iron. There are ceramic brake discs with the ability to heat up to almost 1000 degrees, not prone to deformation, and carbon brake discs. But they are not yet applicable to mass production due to their high cost.
Important! Overheating of the brake discs reduces the effectiveness of the brakes to zero, since in this case they move on the brake disc “like clockwork”.
Why do brake discs overheat?
Naturally operational reason. Friction is the basic operating principle of a car's braking system and is unlikely to change in the near future. The brake system involves: brake discs and brake pads. The heating process of the brake disc occurs in a split second during braking, but cooling is delayed.
Taking into account the fact that 80% of the time we move in the urban cycle, the brake discs constantly heat up. And if your driving style is overly aggressive: acceleration and braking, then overheating of the brake discs is guaranteed.
Malfunction of the brake mechanism. This is a less common reason that causes brake discs to overheat. After all, if you are interested in your safe movement, self-diagnosis of the brake system: checking the brake fluid level, checking the serviceability of both is carried out systematically.
However, you need to know that the reasons for overheating of brake discs can be the following:
- the thickness of the brake pads is below the minimum permissible; as a rule, overheating of the brake discs occurs when the owner abuses the quantity;
- the brake disc is warped;
- the quality of the brake pads leaves much to be desired;
- rear brakes are drum type. Everything is simple here. The lower efficiency of drum brakes leads to the fact that the main load during braking falls on the front disc brakes, which is why the brake discs installed on the front axle overheat.
How to prevent and correct overheating of brake discs
Based on the listed reasons why brake discs traditionally heat up, we accordingly apply methods to eliminate overheating. Timely and timely installation of brake pads, installation of high-quality brake pads and brake discs, it is desirable to use disc brakes on both axles, monitor compliance of the thickness of the brake disc with the established parameters.
Food for thought for car owners
Try, especially in the summer, to avoid washing your car immediately after driving. Brake discs heat up instantly, but cool down a little longer, so when you drive up to the car wash, give the discs time to cool down. This way you will keep the brake disc from deforming. After all, we all remember the school physics course: a sharp temperature shock of heating and cooling leads to deformation. The brake disc is no exception.
Steel, as the main material from which the brake disc is made, turns yellow at t - 150-280 degrees C; turns blue - at 300 - 450 degrees; turns black – 450-500 degrees. Therefore, visual diagnostics of the condition of the brake discs will help you avoid troubles while driving.
Good luck while driving, and do not allow your car's brake discs to overheat.
Heat is normal. The increase in temperature occurs due to friction between the brake disc and pads. The average operating temperature of a brake disc on a modern car is 200 – 300 degrees, however, during aggressive driving with frequent braking, the temperature can reach up to 500 - 700 degrees. Overheating of brake discs can be dangerous because the pads do not make contact with the disc, but literally “slide” over it, reducing braking efficiency.
Causes of brake disc overheating
The most common cause of brake disc overheating is driving style. The more aggressively you drive and the more often you have to brake hard, the more likely it is that your brake rotors will overheat.
![](https://i1.wp.com/blamper.ru/steady/55/41/f5/original/5541f5e7bc33daab2c8b4654/565x565_none.jpg)
In addition, brake discs can overheat due to malfunctions or features of the vehicle's braking system:
- brake disc or pads worn out beyond the permissible norm,
- brake disk warped(needs replacement),
- poor quality brake pads,
- drum rear brakes(since this type of brake is less effective, the main load when braking falls on the front brakes).
How to prevent brake discs from overheating
Knowing the reasons why the brake disc overheats, it is easy to derive rules that will prevent this from happening.
- Firstly, this moderate driving style no sudden braking.
- Secondly, this timely maintenance of brake system components, regular replacement of pads and discs.
- Thirdly, use quality components.
In addition, you should not wash your car immediately after stopping (especially in summer). Brake discs need time to cool, so sudden changes in temperature can cause the brake disc to warp.
How to determine overheating of brake discs
Only a specialist can carry out a full diagnosis of the brake system (including brake discs), but you can carry out a visual inspection yourself. You can determine the condition of the brake discs and the temperature to which they heat up by the color of the steel from which the disc is made:
- yellow – temperature 150-280 degrees,
- blue – temperature 300-450 degrees,
- black – temperature 450-500 degrees.
Serviceable service brakes are like a fire extinguisher, almost no one thinks about them or remembers them once again, however, if, as they say, God forbid, for example, there is an accident or emergency braking, we state their malfunction and “all stones fly into them.” side." Although, by and large, they themselves are to blame, because at one time they did not pay attention, forgot or “forgotten” about their condition, and therefore about their safety, so it seems to me that now we have to blame ourselves.
In short, in order not to feel sorry for yourself later and not to slander fate, you need to regularly diagnose the brake system yourself or with the help of specialists, namely: check the level of brake fluid, the condition of the brake pads, the tightness of all connections and the integrity of the brake disc.
There are many factors that affect the operation of the braking system, or rather its individual elements, among which overheating of the brake discs is not the least important.
Heat– norm for brake disc
For those who do not quite understand how brakes work, I will give a short excursion. The material from which the brake disc is made is subject to high loads, so strength - first of all, strong friction occurs during braking, therefore, in addition to strength, the disc must conduct and give off heat well, be resistant to sudden heating and have a low adhesion ability.
It would seem like some kind of “piece of metal” of a round shape, but there are so many requirements for it. I am sure that you did not know that the operating temperature of this “piece of metal” reaches 200-300 degrees Celsius, which is why metals such as cast iron and steel are used in its manufacture. Analogues of steel discs - ceramic brake discs boast the ability to withstand heat equal to 1000 degrees, while they are not able to deform. However, their main drawback is their high cost, which, by the way, is the reason that they are still not used in mass production.
What are the dangers of overheating brake discs?
Overheating can result in zero brake efficiency, since after this the brake pads begin to interact with the brake disc like oil...
What causes brake discs to overheat?
Of course, the cause of overheating is friction. So what happens, you ask, is to stop slowing down altogether? The answer is no, you just need to think about it more often and change your driving style from aggressive to even, without jerking and sudden braking. You must understand that heating occurs in a matter of seconds, and cooling takes much longer. Therefore, in order not to need to brake too much, it is necessary to avoid aggressive driving. The only place where frequent use of the brakes is justified is driving in city traffic, it is difficult to do anything here, the brake discs, as well as the brake pads, constantly heat up. However, if you continue to “provoke” overheating of the discs by constant acceleration and braking, you are guaranteed to overheat the brake discs.
Reasons for overheating of brake discs:
1. The thickness of the brake pads is below the permissible level. Often overheating of brake discs occurs due to the fault of the owner who abuses the number of grooves in the brake discs;
2. Disc warped;
3. Poor quality brake pads;
4. Rear brakes - drum type. Well, everything is quite simple here, due to the low efficiency of drum brakes, the main load falls on the front disc brakes, which actually contributes to overheating of the front axle brake discs.
Useful tips for car owners
In the summer, try to avoid washing your car immediately after driving for a long time. Remember what I said at the beginning, “brake discs heat up very quickly, but cool down much longer,” so when going to the car wash, give the discs, as well as other heated parts, time to cool down. This will allow you to get rid of such an unpleasant phenomenon as deformation of the brake disc, as well as microcracks that arise from temperature changes.
Hello dear four-wheeled fans! Vehicle! Today we will once again return to the topic of safe car operation. One of the components that is directly responsible for traffic safety is the car’s braking system. After scrolling through several thematic car enthusiast forums, we discovered that many car enthusiasts ask the question: “Why do brake discs get hot and what needs to be done to avoid overheating of the brake mechanism?”
Overheating of the brake disc or discs - current problem, and if you look at requests from regions with mountainous terrain with long descents and ascents, then this problem arises on almost every car. The power of manufactured cars is increasing, the number of divisions on the speedometer is increasing, therefore, the braking system must withstand significant loads and must perform its functions at any time.
What is normal brake disc temperature?
When the driver presses the brake pedal, the brake discs grip the brake disc on both sides and the friction effect stops the car. But, as you know, where there is friction, there is heating and, accordingly, an increase in temperature.
The loads experienced by the brake system, especially during emergency braking, can heat the brake disc to critical temperatures. Although auto manufacturers use modern materials in the production of components and parts of the brake system, they also have their limitations.
High temperature of the brake disc can lead to deformation of the disc itself, overheating and boiling of the brake fluid.
Today we will not consider discs designed for sports cars; our goal is standard brake discs that can be bought at any store. The main components of these discs are steel and alloy cast iron. By understanding what a particular disk is made of, you can predict what will happen to the disk if it is overheated or, worse, when a disk heated to 300 degrees (by the way, the normal temperature of a disk is 200...300 degrees) falls into a puddle.
The temperature difference will negatively affect the geometry of the brake disc, and the disc will begin to “rub” the pads and the situation will only worsen.
Therefore, the driver should pay attention to the road situation and try to avoid puddles, especially after repeated braking.
For their part, brake disc manufacturers produce discs that meet the following requirements:
- strength and manufacturing precision;
- maximum friction coefficient;
- low corrosion;
- high thermal conductivity of disks;
- practically no adhesion;
- resistance to thermal shock;
- the material must be stable when heated.
Why does the disk get hot?
Above, we have already written that the reason why the disk heats up is the friction process. And what is not unimportant is that if the disc heats up instantly from contact with the pad, then it does not cool so quickly (ventilated discs can cool faster compared to solid ones).
In order to understand how hard it is on the braking system, just count how many times you pressed the brake while driving from your home to the nearest intersection, and if you add the high air temperature, you will understand everything.
On the process of "warming up" the disks significant influence The driving style also has an effect - if it is sporty and in the city you alternate between emergency braking and sharp acceleration, then the disc simply will not have time to cool down.
Failure of brake system components is the most common cause of excessive heating of brake rotors. If worn out pads are not replaced in time, then this situation is unlikely to have a positive effect on the temperature regime and the performance of the entire brake mechanism assembly.
Here is a list of the most common breakdowns that can affect the temperature:
- the disk is warped;
- the thickness of the disc and pads do not correspond to those recommended for this model (both negative and positive);
- pads or discs were purchased of dubious quality;
- different types of braking devices on the front and rear axles (with drums installed on the rear wheels, the front axle experiences significant loads).
How to determine the condition of a disk by eye?
First, we will give some useful advice: in order to preserve the geometry of the brake discs, do not wash the car immediately after finishing driving, let them cool.
And so, we determine by eye the temperature of the brake disc:
- if the surface of the disk is yellow, then the temperature of the disk for a long time was 150-280 C;
- the disk will have a blue tint after heating to 300-450 C;
- well, it will turn black at a temperature of 450-280 C.
We wish you and your friendly family good luck.
When braking, the process of friction between the brake pad and the wheel occurs at the points of their actual contact. The total area of these contacts is insignificant compared to the area covered by the brake pad. Since the release of heat occurs only at the points of actual contact, the heat flux densities and temperature flashes in them can reach large values, causing the friction surface to glow and the transition of the metal at these points to a plastic state. In this case, deformation of the metal or its rapid wear occurs, and the location of the temperature flash moves in accordance with the change in contact specific pressures.
The spread of heat flow over the entire friction area occurs close to the contact surface, and its density sharply decreases compared to the points of actual contact, acquiring a value corresponding to the geometric dimensions of the contacting bodies. The temperature in the surface layers changes accordingly.
It should also be borne in mind that the temperature of any point on the tread surface of the wheel for each revolution has some fluctuations, which are a consequence of the fact that when the point in question leaves the contact zone, there is a slight decrease in temperature due to heat removal into the wheel and into the environment; When passing the point in the contact zone of the wheel and the brake pad, its temperature rises and exceeds the calculated average value. However, when solving thermal problems, this phenomenon can be neglected due to the inertia of the processes and the heat supply over the entire friction surface of the wheel can be considered continuous. Thus, to calculate this temperature Dtp at any moment of braking time I, you can use the following expression
The highest temperature during stopping braking on the surface of the wheel is achieved in the middle of this process I = 0.5*v Temperature on the surface of the wheel at the moment the train stops
![](https://i1.wp.com/dieselloc.ru/books/asadchenko/images/image_187.png)
![](https://i2.wp.com/dieselloc.ru/books/asadchenko/images/image_188.png)
Temperature during steady braking (at constant speed)
![](https://i1.wp.com/dieselloc.ru/books/asadchenko/images/image_189.png)
where Оф is the coefficient of heat transfer to the environment, kcal/m2s °C; dr - heat flux density, kcal/(m2s); X - thermal conductivity coefficient, kcal/(ms °C); y - specific gravity, kgf/m3; With - specific heat, kcal/(kg °C); g - braking time to stop, s.
The values of X, y, c are given in table. 7.1.
Temperature coefficient values Table 7.1
The heat flux density at the initial moment of braking is determined by the formula
![](https://i1.wp.com/dieselloc.ru/books/asadchenko/images/image_190.png)
where aL is the dimensionless heat flow distribution coefficient; Ak is the width of the wheel friction surface, m (taken equal to 0.09 m).
The heat flow distribution coefficient for the wheel can be determined from the data given in table. 7.1 (for pads ak=1-aL).
The above formulas were obtained for heating conditions of a semi-bounded body, i.e. when the heat flow does not yet reach the surface limiting the heated body on the side opposite to the heat supply. This assumption is acceptable when heating bodies of sufficiently large thickness. In the majority of braking modes realistic for operating conditions, excluding particularly long ones, these formulas can be recommended for calculations. In the latter case, there are special adjustment factors determined from the graphs.
A preliminary estimate of the heat transfer coefficient depending on the speed (m/s) can be made using the empirical formula (7.3).
Table 7.2
Heat flow distribution coefficient values
Due to the fact that the braking force changes during the filling of the brake cylinders and when the speed changes, the value of At is calculated based on the length of the actual braking distance 5T and the brake preparation time 1p
![](https://i2.wp.com/dieselloc.ru/books/asadchenko/images/image_191.png)
where (Od is the main specific resistance to train movement (taken equal to 2 N/kN).
In this case, time I in the expressions for calculating thermal conditions is taken to be reduced by the preparation time 1l, if 1 > 1.
Based on expressions (7.1), (7.2), we obtain a formula for determining the diameter of the wheel d, which provides the necessary heat convection to avoid its overheating during emergency braking
![](https://i2.wp.com/dieselloc.ru/books/asadchenko/images/image_192.png)
When braking, the kinetic energy of the train turns into thermal energy, heating the brake pads (or discs) and wheels. Considering that with an increase in the speed of movement, for example, the amount of this energy quadruples, the thermal stability of the friction pair becomes especially important, the violation of which leads to the loss of frictional qualities and the occurrence of emergency situations on the rolling stock.
The permissible amount of pressure A",4 (kN) on a cast iron brake pad according to the thermal regime during stopping braking can be found from the expressions where K0 is the initial braking speed, m/s;
![](https://i2.wp.com/dieselloc.ru/books/asadchenko/images/image_193.png)
^tmax is the maximum permissible temperature of the brake pad during stop braking, °C (for cast iron - 600 °C, for composite ones - 400 °C);
Od - coefficient of heat transfer to the environment.
Similarly, the maximum pressure under temperature conditions for composite pads is determined by the expression
![](https://i2.wp.com/dieselloc.ru/books/asadchenko/images/image_195.png)
The stopping braking time I (s) with a braking distance known according to the standards is 5T (m) on a given slope from the initial braking speed K0 (m/s) is based on the assumption of uniformly slow motion
During the braking process, significant heating of the tread surface and nearby layers of the wheel occurs. At the same time, for the wheels of traction rolling stock, the tires of which are pressed on in a heated state, there is a risk of them turning and sliding. The criterion for the permissible weakening of the tension of the tire is its increase in millimeters per 1 m of the wheel diameter, which should not exceed 1.2 mm:
for emergency braking
![](https://i1.wp.com/dieselloc.ru/books/asadchenko/images/image_197.png)
for service braking in long-term mode where the braking distance is 50, respectively, when a locomotive travels with a train and alone, m;
![](https://i2.wp.com/dieselloc.ru/books/asadchenko/images/image_198.png)
Vts, N - thickness and width of the bandage, respectively, m;
\U - work during braking for time 1, per one wheel, Nm;
Re is a coefficient that takes into account the share of energy perceived by the dynamic brake.
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