Responsible for the safety of the driver and passengers while driving. It consists of a large number of components and assemblies. The balanced operation of all components of the system is what you need to strive for. We will talk with you about what DOT-4 brake fluid is, which one is better and what to look for when choosing. We'll start with fundamental concepts.
About brake fluid and its functions in the system
When the driver presses the brake pedal, the pads are pressed against the discs, thereby bringing the car to a standstill. During braking, a huge amount of heat is generated that must be removed from the system. This can be done using a special liquid. It must have a number of properties. This:
- low compressibility;
- high boiling point;
- stable viscosity;
- a small level of absorption;
- do not destroy rubber gaskets and seals.
All these properties are indispensable for the effective operation of the braking system. And since cars are constantly being improved, their power and weight are increasing. Accordingly, the braking effort must be high. Hydraulic brakes are preferred in this regard. They work quickly and smoothly and are also very reliable. The brake fluid must be renewed. Today there are DOT-3, DOT-4 and DOT-5.1.
What is very important
Boiling point is one of the most important indicators of high-quality brake fluid. The fact is that because of the heat given off by the pads and the disc into the system, ordinary liquid will boil. This leads to the formation of bubbles in the system and the formation of an air lock or complete failure. On the road, such a situation is likely to lead to an accident.
That is why brake fluid manufacturers try to maximize the boiling point. After all, this gives more reliability. We all know that the viscosity characteristics of a liquid change with its temperature. This should not happen in brake fluid. Let's take a closer look at what DOT-4 brake fluid is, which one is better, and other important points.
Difference between DOT-3 and DOT-4
DOT-3 brake fluid is gradually being decommissioned. This is due to the emergence of more advanced formulations. A feature of DOT-3 is its low cost, which is due to the presence of dihydric alcohols (glycols). This component significantly increases hygroscopicity. Consequently, over time, water appears in the system, and this leads to a decrease in the boiling point and the appearance of corrosion.
More modern and high quality brake fluid - DOT-4, which consists of esters and boric acid. The acid neutralizes moisture on contact, so there is no such drawback as hygroscopicity. Consequently, the system can remain out of service for a considerable time, because the boiling temperature does not change for a long time.
Brake fluid DOT-5.1 and its features
The main difference is the higher boiling point. The chemical composition is similar to DOT-4. It is often used in racing cars and motor vehicles, where high speed develops and prolonged intensive braking is characteristic.
It is worth remembering the rules for mixing brake fluids. If DOT-3 is filled in, then you can top up DOT-4 and DOT 5.1. And if in the DOT-5.1 system, then only the analog is added. Failure to comply with this rule can lead to jamming of the system and failure of the brake mechanism with all the ensuing consequences. It turns out that the compatibility of the DOT-4 brake fluid is reduced to adding more advanced DOT-5.1. This is not always convenient, although it is correct from a technical point of view.
What kind of brake fluid to fill in the system?
This question worries many motorists. First of all, it is necessary to be guided by the recommendations of the manufacturer. Most of the cars of the VAZ family are operated on DOT-3, although DOT-4 is perfect for them. This is the best option both in terms of price and quality.
At the same time, it is not recommended to use DOT-3 on foreign cars, although it is permissible. This is due to the low boiling point, which can damage the brakes. For moderate driving, brake fluid DOT-4 is suitable. Which is better? But with this we will figure it out now.
Brake fluid "Lukoil DOT-4"
The boiling point of this liquid is 170 degrees (humidified) and 240 (dry), which is quite suitable for the standard, even with a small margin. Lukoil DOT-4 occupies a fairly high position in the rating due to its stability and high quality. In addition, the low cost of the product makes it more affordable for the consumer.
There are practically no fakes of "Lukoil DOT-4" on the market, since the products are well protected and have a low price. In general, this is a worthy contender for the title of the winner, but we will consider a few more options.
Sintec Euro and Sintec Super
This is another domestic manufacturer of a quality product. Sintec Super DOT-4 brake fluid has a small temperature margin compared to that indicated on the can. True, for some reason they don't add a little on the conveyor, but given the quality, this is not a big deal.
"Sintec Euro" has a higher price tag, but also significantly differs from the previous brake fluid. The canister indicates the temperatures at which the system will work properly. But testing has shown that the liquid boils at a higher mark. Therefore, we have a large margin in terms of temperature and a fairly high quality. The liquid does not change its properties with increasing temperature and "works" quietly for several years.
Castrol React DOT4 Low Temp
A half-liter can from this manufacturer costs about 450 rubles. Not the cheapest option, but one of the best. The boiling point in a wet state is 175 degrees, and in a dry state - 265 degrees Celsius. According to the regulations, replacement is made every two years of operation.
It is worth noting that DOT-4 Low Temp brake fluid is excellent for use at critically low temperatures. The manufacturer deliberately lowered the viscosity of the liquid to 650 mm 2 / s. Looking at the test results and characteristics of this liquid, we can say that this is a full-fledged DOT-5.1. Nevertheless, DOT-4 liquid is more in demand on the market, therefore it is more expedient to sell it. The composition of the brake fluid DOT-4 from Castrol differs from its analogues in the package of additives that increase the boiling point.
Liqui Moly Bremsflussigkeit DOT-4
This is another sales leader in the Russian market. The price tag here is not as big as that of Castrol. A half-liter can will cost you 300 rubles, which is quite a bit. The threshold for boiling fresh liquid is 250, and about 165 degrees Celsius. Viscosity - 1800 mm 2 / s. In general, "Liquid Moli" fits into the framework of the DOT-4 standard, but nothing more. However, it is worth giving preference to "Castrol", but if funds are not enough, then "Liquid Moli" is perfect.
It is worth noting that the manufacturer has focused on protecting the brake system from corrosion. They did it wonderfully well, as evidenced by the experimental data. There are no signs of rust throughout the entire service life. The company also paid great attention to the lubricating properties of the liquid. It can be recommended for use in the central part of Russia and to the south. "Liquid Moli" can be mixed with DOT-3 and DOT-4, it is not recommended with DOT-5.
RosDOT-4 at a glance
In this case, the domestic manufacturer paid special attention to temperature characteristics. Fresh liquid boils at 255 degrees, and operated throughout the year - at about 170 degrees. The Dzerzhinsky plant produced a really high-quality product, which surpassed "Liquid Moli" in its properties and characteristics. The domestic product has an affordable cost and is widely distributed in all stores in the Russian Federation. Here you will not see anything unusual - this is an ordinary "brake" at an affordable price.
As you can see, the best DOT-4 brake fluid is produced by Castrol. Despite the high cost, it is very, very good.
How to make the right choice?
Everything here is extremely simple and straightforward. Much depends on your riding style. If you prefer an aggressive demeanor on the road, then it is better to choose "Castrol", which, although it is positioned as a DOT-4, but its characteristics speak of a higher class.
For a quieter and measured ride, any of the domestic manufacturers is perfect. True, it is important here to pay attention to the viscosity of the liquid at subzero temperatures. For northern regions, it is desirable to give preference to more fluid fluids.
Another important point before deciding which brake fluid to fill is to save the brake system. In this case, it is best to choose "Liquid Moli". It is from this manufacturer that the brake fluid shows the best results. It does not lead to corrosion, but, on the contrary, protects the system from it, which is very good.
Regular system maintenance
It is very important to lubricate the calipers in time, change the anthers and guides. This also applies to discs with pads, which wear out during operation. The braking system on a modern car is quite complex. Consists of an ASB block, highways, etc. All elements must be monitored. Only then can you be sure that the brakes will not fail during extreme braking.
It is recommended to use graphite and copper lubricants to service the brake system. They are needed so that when replacing a part, it is easier to replace it. Indeed, due to high temperatures, the metal very often sticks, copper spray does not allow this.
As for the brake fluid, it is still recommended to use the one prescribed by the manufacturer. Usually, the manufacturer simply indicates the marking, for example, DOT-3 or DOT-4, without any specification. In this case, you are guided by yourself based on your preferences. The choice should be influenced by factors such as:
- driving style;
- the state of the braking system;
- corrosion protection;
- product cost.
Coming to completion
Brake fluid "Castrol DOT-4" is very good. But it costs a lot of money. Therefore, we often give preference to budget counterparts. There is nothing terrible in this. The main thing is to pay attention to the following details: the boiling point of the "dry" liquid should be at least 250 degrees, and the "humidified" - 150. If the canister contains smaller numbers, then it is better to bypass such a product. Also, at least a minimum should be provided. protection against corrosion of the system. It is extremely important, because replacing all lines and calipers will cost you a penny. The medium should be either neutral or slightly alkaline, but in no case acidic.
There are fairly high-quality Russian-made liquids. These include "Felix" and "Lux". The latter option is not suitable for the northern regions, as it thickens strongly at low temperatures. But "Felix" is a great alternative for many. It combines the positive qualities of Castrol and boasts corrosion protection like Liquid Moli. So we learned what the DOT-4 brake fluid is. Which is better? There is an absolute leader here - "Castrol" and several noteworthy domestic manufacturers, which are recommended to stop at.
Brake fluid is a very important component of any car. From the name it is clear that it is poured into the brake system and directly contributes to braking, that is, the system works on a hydraulic principle. But pouring into the system, do not understand that it is impossible! There are many reasons for this; special formulations with certain properties are used here. Today I want to tell you what they are made of and why they must be changed ...
By the way, the following questions came to my blog - “tell me, is it possible to pour ordinary water into the brake system? And that will be?" One can see a young inquisitive mind, as they say - comprehends the world! Read on and you will understand everything.
A few words about the braking system
I just want to remind you how it works. Any car has a brake pedal, if "grossly exaggerated" it is associated with the brake slave cylinder. After you press this pedal, pressure is created in the brake system, it presses on special pistons in the brake calipers (or rear cylinders) which compress (in the case of front-wheel drive) or spread (in the case of rear) brake pads. And already they, in turn, squeeze the brake disc or stop the drum from the inside, I advise you to read -.
I think everyone knows the principle of operation of this system, in our article it is necessary for the next understanding of the material.
Warming up the system
The discs or drums get very hot when braking. Actually, this is a law of physics, friction occurs - brake pads rub against a metal surface, a large release of heat occurs. The pads are made of a special "thermo" and "wear-resistant" material, so they can walk for a very long time, this material does not heat up so much when compared with discs or drums.
But their warming up can be just catastrophic (especially at the front axle) on the Internet there are a lot of videos where they heat up to "red".
And what happens is that parts of the brake system, namely pistons, cylinders, and even experience huge temperature loads. At high speeds, temperatures can go up to 150 degrees Celsius. Do you understand what I mean? Actually, now let's start talking about the compositions.
What can and cannot be filled
Now I want to answer the reader - let's analyze ordinary water. Why it CATEGORALLY CANNOT be flooded. YES, in fact, everything is simple - even if you do not dig deep, the water boils and evaporates at high temperatures, and at low temperatures it freezes at -1 degrees. You come this winter, start the car, but there are no brakes! The system is frozen! Also imagine - the system boils when braking, steam is pouring out of the system reservoir, the efficiency is at zero. However, even if we hypothetically defeat freezing and boiling, then water has ONE BIG LACK - it oxidizes and provokes rust, after a short period of time, the pistons in the calipers will simply rust, the oil seals that are designed to walk on a smooth and clean surface will rupture and water will leak out.
Alcohols (in pure form) are also not suitable, because they boil, and even ignite.
Transmission oils, motor oils - oils may be suitable, but again, not all.
Their evaporation is really low, they also perfectly withstand high temperatures (especially motor ones), but at low temperatures they can thicken (this negatively affects fluidity), and they can also negatively affect the rubber of the oil seals! That is, calipers or cylinders may leak.
Different formulations of brake fluid
So what did we understand - that the brake fluid must have a high fluidity, lubricate, protect against corrosion, not freeze, withstand temperatures in the range of 150 - 170 degrees Celsius, not boil! That is, such - "super liquid".
Probably, I will not surprise anyone by saying that the "brakes" are still evolving - WELL, THERE IS NO IDEAL COMPOSITION NOW THAT WOULD MEET ALL REQUIREMENTS BY 100%.
Mineral compositions - it all started with them, I will say that they were used on old cars, which did not even have front disc brakes, only drums. YES and speeds at that time rarely exceeded 60 km / h.
Their composition has long been known - castor oil with the addition of butyl or ethyl alcohol, this is a kind of base, but many manufacturers have mixed other minerals and petroleum products of varying degrees of purification into the composition. It is difficult to call such a composition ideal, but there are still positive aspects:
- They lubricate well
- They practically do not absorb moisture, that is, if we say "scientifically" they have low hygroscopicity
However, there are much more disadvantages:
- At temperatures of 110 - 130 degrees, they boil
- At -20 degrees they begin to thicken
- In addition, castor oil has a negative effect on parts made of brass, aluminum, copper
- Also for a long time they could not find a formula that, over time, would not decompose rubber products, oil seals, cuffs, etc.
They fought for a very long time precisely on the formula with castor oil, added all kinds of additives and other substances, but its time had already passed.
Glycolic brake fluids - now they are used quite widely, you can know by abbreviations (DOT3, DOT4, DOT 5.1). They have polyethylene glycols and boric acid polyesters in their compositions that meet all international standards, and have also passed the Russian GOST certification.
This composition is almost perfect, boils at + 150, + 200 degrees, lubricates perfectly, protects against rust, is almost neutral to rubber elements.
There is one minus here and quite large - high hygroscopicity, they absorb moisture very strongly, therefore, it is MANDATORY to change completely every 2 - 3 years! Otherwise, the calipers begin to sour and rust.
Silicone brake fluids (DOT5 and DOT-5.1 / ABS special version). The composition here is completely different from its counterparts, based on organosilicon polymers. There are enough pluses - it does not absorb moisture, is absolutely neutral to rubber and metals, always fluid (does not depend on temperature).
There are also disadvantages, but where without them - the lubricating properties are at a low level, so there is more wear on the oil seals (when compared with the brothers). Such formulations are rarely used on production versions of cars, as a rule, they are poured into sports or racing cars, where the heating of the calipers is much higher.
In the proposed article, we will tell you why the car is so important, what properties it possesses and when it is necessary to replace it.
Brake fluid actuates the hydraulic drive. Namely, the pressure is transmitted from the main brake cylinder, which obeys the brake pedal, to the wheel brake cylinders. The latter, thanks to the brake pads, slow down the movement. Now imagine what the consequences could be if this whole process does not proceed efficiently, and the car stops moving later than necessary?
Brake fluid requirements:
- firstly, it must perform its functions at any temperature: be it minus 30 or plus 150 (the temperature in the brake cylinders at the time of intensive braking);
- secondly, it must react well with metals and rubber parts-seals of the hydraulic system;
- thirdly, the brake fluid must have high lubricating properties. This condition is very important for brake cylinders, namely for their inner surfaces;
- fourthly, the properties of the brake fluid should not depend on the operating conditions.
Based on the above requirements, it is created, which contains 92-98% of the base and special additives.
Types of brake fluid.
Depending on what is included in the basis, such brake fluid types:
Mineral. It has a low cost, high lubricating properties. Its aggressiveness towards rubber is very low. Main disadvantages:
- at temperatures less than minus 20, it is quite viscous;
- the boiling point is quite low.
This is used brake fluid type only in older cars, as it is neutral to rubber seals.
Glycolic. It contains ethers and polyglycols. This base is very popular due to its high performance properties. Increased hygroscopicity is its main disadvantage.
Silicone. Most modern and completely non-hygroscopic. It is used very rarely because:
- incompatible with other types of stems;
- poorly compatible with rubber parts;
- has increased requirements for the quality of pumping;
- quite expensive.
The main properties of the brake fluid.
Boiling temperature. When the liquid boils, vapor is released, which is compressed. This process leads to the fact that the pedal "fails" and there is no braking. Often this problem occurs when the brakes are often slowed down. It is in this situation that the heat from friction is not removed from the brake system in time, and the overall temperature increases.
Viscosity at various temperatures. Critical cases: thickening at low temperatures or increased fluidity at high temperatures.
How often do you change the brake fluid?
Experts recommend producing replacement of brake fluid every two to three years. Because of the difference in operating temperatures, the brake fluid easily absorbs moisture from the air and even during condensation. This ability leads to low lubrication in the warm season and thickening in the cold season. And the worst thing is that it is enough to dissolve only 3% of water in the brake fluid in order to reduce the boiling point by 70 degrees. It is this fact that serves as the main reason for the replacement.
Change brake fluid it is possible earlier, if you find impurities, or notice that the transparency has decreased. However, it is quite difficult to objectively assess the state of the liquid, because it does not mix in the system. Consequently, different properties of the brake fluid are observed in the reservoir and in the working cylinders.
What kind of brake fluid do you need to fill?
The most important condition is to follow the manufacturer's requirements, since the braking system is designed for certain parameters. brake fluid... Do not forget that quite often the manual prescribes how often it needs to be replaced.
Mix brake fluid or not mix?
Mixing is strictly prohibited. brake fluids different classes! Since there is a possibility of incompatibility of additives, it is also not advised to mix fluids from different manufacturers, even if they are within the same class. Use only the brake fluid specified by the manufacturer.
How to add brakes correctly?
Everything is very simple here, the main thing is to remember which one was previously filled into the car. Buy the same one and add it to the brake reservoir. Be sure to keep it at the "max" mark. As practice shows, with a working brake system, it has to be refilled once a year.
One of the fluids important for the normal operation of a car is brake fluids. About what this fluid is needed for, how often it needs to be replaced and what kind of brake fluids to use for optimal operation of the machine's braking system - in our today's article.
The role of brake fluid in the "body" of a car
The braking system, which is responsible for the timely stop of the car and therefore plays an important role for the safety of the passengers of the car, cannot work without brake fluid (TK). It is she who performs the main function of the brake system - it transfers through the hydraulic drive the force from pressing the brake pedal to the brake mechanisms of the wheels - pads and discs, as a result of which the car stops. Therefore, even in driving schools, novice motorists are strongly advised to periodically check the levels of four service fluids: glass cleaner and brake fluid, on which the optimal operation of the car depends.
Composition and properties of brake fluids
The basis of the chemical composition of most brake fluids is polyglycol (up to 98%), less often manufacturers use silicone (up to 93%). In the brake fluids used on Soviet cars, the base was mineral (castor oil with alcohol in a 1: 1 ratio). It is not recommended to use such fluids in modern cars because of their increased kinetic viscosity (thicken at -20 °) and low boiling point (at least 150 °).
The remaining percentages in polyglycol and silicone TK are represented by various additives that improve the characteristics of the brake fluid base and perform a number of useful functions, such as protecting the surfaces of the working mechanisms of the brake system or preventing the oxidation of TK as a result of exposure to high temperatures.
It is not for nothing that we dwelt in detail on the chemical composition of brake fluids used in cars, since many motorists are interested in the question - "is it possible to mix technical specifications with different chemical bases?" We answer: Mineral brake fluids are strongly not recommended to be mixed with polyglycolic and silicone fluids. From the interaction of the mineral and synthetic bases of these fluids, clots of castor oil can form, which clog the lines of the brake system, and this is fraught with malfunctions of the brake system. If you mix mineral and polyglycolic TK, then this "hellish mixture" will be absorbed into the surface of the rubber cuffs of the brake hydraulic drive parts, which will lead to their swelling and loss of sealing.
Polyglycolic TZ, although they have a similar chemical composition, and can be interchangeable and, but mixing them in one brake system is still not recommended. The fact is that each manufacturer of technical specifications can change the composition of the additives at its discretion, and their mixing can lead to a deterioration in the main operational characteristics of the working fluid - viscosity, boiling point, hygroscopicity (ability to absorb water) or lubricating properties.
Silicone brake fluids it is forbidden to mix with mineral and polyglycolic ones, since as a result the working medium is clogged with precipitated chemical substances, which will lead to clogging of the brake system lines and failure of the brake cylinder assemblies.
Classification of brake fluids
Today, most countries in the world have uniform brake fluid standards known as DOT (after the name of the agency that developed them - the Department of Transportation - the United States Department of Transportation) - such markings can often be found on brake fluid containers. It means that the product is manufactured in accordance with the regulatory federal vehicle safety standards FMVSS No. 116 and can be used in the braking systems of cars and trucks, depending on the technical characteristics of these vehicles. In addition to the American standard, brake fluids are labeled in accordance with the standards adopted in a number of European and Asian countries (ISO 4925, SAE J 1703 and others).
But they all classify brake fluids according to two parameters - their kinematic viscosity and boiling point. The first is responsible for the ability of the working fluid to circulate in the brake system line (hydraulic drive, pipes) at extreme operating temperatures: from -40 to +100 degrees Celsius. The second is to prevent the formation of a vapor "plug" that forms at high temperatures and can lead to the brake pedal not being triggered at the right time. When classifying TZ by boiling point, two states are distinguished - the boiling point of a liquid without impurities of water ("dry" TZ) and the boiling point of a liquid containing up to 3.5% water ("humidified" TZ). The "dry" boiling point of the brake fluid is determined by a new, freshly poured working fluid, which did not have time to "collect" water and therefore has high performance characteristics. The “humidified” boiling point of TK refers to a working fluid that has been in operation for 2-3 years and contains a certain amount of moisture in its composition. More about this - in the section "Service life of brake fluids". Depending on these parameters, all brake fluids are divided into four classes.
DOT 3. The "dry" boiling point of this brake fluid is not less than 205 °, and the “wet” one is not less than 140 °. The kinematic viscosity of such a TZ at + 100 ° is not more than 1.5 mm² / s, and at -40 - not less than 1500 mm² / s. The color of this brake fluid is light yellow. Application: intended for use in cars, the maximum speed of which is not more than 160 km / h, in the braking system of which disc (on the front axle) and drum (on the rear axle) brakes are used.
DOT-3
DOT 4. The "dry" boiling point of this brake fluid is not less than 230 °, and the "wet" one is not less than 155 °. The kinematic viscosity of such a TZ at + 100 ° is not more than 1.5 mm² / s, and at -40 - not less than 1800 mm² / s. The color of this brake fluid is yellow. Application: intended for use in vehicles with a maximum speed of up to 220 km / h. The braking system of such vehicles is equipped with disc (ventilated) brakes.
DOT 5. The "dry" boiling point of this brake fluid is not less than 260 °, and the "wet" one is not less than 180 °. The kinematic viscosity of such TZ at + 100 ° is not more than 1.5 mm² / s, and at -40 - not less than 900 mm² / s. The color of this brake fluid is dark red. In contrast to the above TK, DOT 5 is based on silicone, not polyglycol. Application: intended for use on special vehicles operating in conditions of extreme temperatures for braking systems, and therefore is not used on ordinary cars.
The "dry" boiling point of this brake fluid is not less than 270 °, and the “wet” one is not less than 190 °. The kinematic viscosity of such TZ at + 100 ° is not more than 1.5 mm² / s, and at -40 - not less than 900 mm² / s. The color of this brake fluid is light brown. Application: intended for use in braking systems of sports racing cars in which the temperatures of working fluids reach critical values.
Pros and cons of brake fluids
All of the above brake fluids have their own advantages and disadvantages. For convenience, we will indicate them in the table below:
| TK class | Dignity | Flaws |
| DOT 3 |
|
|
| DOT 4 |
|
|
| DOT 5 |
|
|
| DOT 5 .1 |
|
|
When to change the brake fluid?
The service life of the brake fluid directly depends on its chemical composition.
Mineral TK, due to its chemical characteristics (low hygroscopicity, good lubricating properties), has a rather long service life (up to 10 years). But when water enters the liquid, for example, in the event of a depressurization of the brake system, its properties change (the boiling point drops, the viscosity rises), and it can no longer perform its functions, which can lead to brake failure. Periodic inspection (once a year) of the brake system and fluid condition, which can be determined in laboratory conditions, is recommended.
Polyglycolic TK has an average or high degree of hygroscopicity, and therefore its condition should be checked twice a year. It is possible to assess the state of polyglycolic TK visually: if the liquid has darkened or precipitation is noticeable in it, then it must be completely replaced. Such TK is capable of absorbing up to 3% moisture per year. If this figure exceeds 8%, then the boiling point of the brake fluid may drop to 100 °, which will lead to boiling of the TK and failure of the entire brake system. Automotive manufacturers recommend changing polyglycol-based brake fluid every 40 thousand kilometers or every 2-3 years. Typically, this brake fluid is completely changed during the installation of new external braking mechanisms (pads and discs).
Silicone TK is distinguished by its durability of operation, since its chemical composition is more resistant to external influences (moisture ingress). As a rule, replacement of silicone brake fluids is carried out after 10-15 years from the moment of filling the brake system.
Reliable operation of the braking system is of course important for the safety of driving a car, therefore special requirements are imposed on the quality and conformity of the brake fluid. But even if it is of high quality and is chosen correctly, over time, its properties will deteriorate early in the process of operation, so it is imperative to observe the correct replacement frequency provided by the manufacturer.
When the brake pedal is depressed, the force is transmitted hydraulically to the wheel brakes, which slow down the vehicle due to frictional forces. If in this case the brake fluid can heat up above the permissible limit, boil and vapor locks form. The mixture of liquid and vapor will be compressed, therefore the brake pedal may "fail" and the braking will be unreliable, and failures may occur. To eliminate such a phenomenon in hydraulic drives, special fluids are used for hydraulic drives of the brake system. They are classified according to boiling point and viscosity according to the DOT (Department of Transportation) regulations adopted by the US Department of Transportation. This takes into account the boiling point of a liquid without moisture impurities (dry), and containing up to 3.5% water. Viscosities are two values at + 100 ° C and -40 ° C. See the table below for these figures (in line with the US Federal Standard). Similar requirements are imposed by other international and national standards - ISO 4925, SAE J1703 and others. In Russia, there is no single standard governing the quality indicators of brake fluids, so manufacturers work according to their specifications.
Application of different classes of brake fluids:
DOT 3 - on relatively slow-moving vehicles with drum brakes or front disc brakes;
- DOT 4 - on modern high-speed vehicles with disc brakes on all wheels;
- DOT 5.1 - on sports cars with higher thermal loads. Liquids of this class are practically not used on ordinary cars.
OPERATING REQUIREMENTS
In addition to the main indicators, boiling point and viscosity, other equally important requirements are imposed on brake fluids.
The liquid should not harm the rubber parts of the car.
Between the hydraulic brake pistons and the cylinders there are rubber cuffs, the tightness of which increases under the influence of the brake fluid. At the same time, rubber joints increase in volume, expansion up to 10% is allowed. They should not swell too much, shrink, lose elasticity and strength.
The brake fluid must protect metals from corrosion.
Metal components in hydraulic brakes can be subject to electrochemical corrosion. To prevent this process, corrosion inhibitors must be added to the brake fluid to protect steel, cast iron, aluminum, brass and copper parts.
Lubrication of rubbing parts.
Brake fluid must be lubricating to reduce wear on the sliding surfaces of the brake cylinders, pistons and lip seals.
Stable at low and high temperatures.
Brake fluids operate in the temperature range from -40 to + 100 ° C. Within these temperature limits, the liquid must retain the properties provided by the manufacturer, with some degree of fluctuation, withstand oxidative processes, delamination, the formation of deposits and deposits.
TYPES AND COMPATIBILITY OF BRAKE FLUIDS
Brake fluids are mineral, glycol and silicone based (about 93-98%), with various additives, additives, dyes.
Mineral base is a mixture in a 1: 1 ratio of alcohol, for example, butyl, and castor oil. Such a liquid has good lubricating and protective properties, is non-hygroscopic, and does not damage the paintwork. But it has significant drawbacks that prevent it from meeting international standards. Mineral-based brake fluid has a low boiling point, it is not allowed to use it on cars with disc brakes, and its viscosity is too high even at a temperature of -20 ° C.
Mixing of mineral and glycolic liquids is not allowed. This can cause excessive swelling of the hydraulic rubber seals and the formation of castor oil clots.
Glycolic brake fluids- based on polyglycols and their esters - a group of chemical compounds of polyhydric alcohols. They have a high boiling point, good viscosity and good lubricating properties. The main disadvantage is hygroscopicity, i.e. the property of picking up moisture from the air through the expansion hole in the reservoir cover of the master brake cylinder. Moisture saturation lowers the boiling point of the glycol fluid, increases viscosity at low temperatures, reduces lubricity and corrosion resistance. All glycol fluids, both imported and domestically produced, of classes DOT 3, DOT 4 and DOT 5.1 are interchangeable, it is allowed to mix them, but this is not recommended. This can lead to a deterioration in their basic properties.
On older vehicles over 20 years old, the rubber seals may not be glycol compatible. Only mineral brake fluids can be used here, otherwise it will lead to destruction of the cuffs.
Silicone brake fluids are made on the basis of organic silicon polymer products. Main advantages: viscosity is practically independent of temperature, inert to various materials, efficient in the temperature range from -100 to + 350 ° C, moisture is not taken from the air. But with all the advantages, such fluids have weak lubricating properties, which limits their use. Silicone fluids do not mix with others.
DOT 5 silicone based fluids should be distinguished from DOT 5.1 polyglycol based fluids, similar names can lead to confusion. Usually, the packaging additionally indicates:
DOT 5 - SBBF ("silicon based brake fluids" - silicone brake fluid).
DOT 5.1 - NSBBF (non silicon based brake fluids).
INSPECTION AND REPLACEMENT
Glycolic brake fluids are mainly used on modern cars, which have a number of advantages. But, unfortunately, in a year, glycol will take up to 2-3% of moisture from the air, and the fluid has to be changed periodically, and in advance, until it becomes dangerous for the reliable operation of the brake system. (see fig). Replacement periods are usually indicated in the vehicle's manual and range from 1 to 3 years.
An objective assessment of the properties of brake fluid is possible only under laboratory conditions, therefore, to save time, the condition of the brake fluid is assessed visually. Its transparency, uniformity, and absence of sediment are assessed. There are also devices for determining the boiling point of the brake fluid and the degree of its moisture.
Since the fluid does not circulate in the system, its condition in the reservoir (test point) may differ from that in the wheel cylinders. In the reservoir, it can pick up moisture from the air, but in the brakes, it cannot. But there the liquid heats up more, sometimes excessively, and its properties may deteriorate.
If you simply add new brake fluid when bleeding the system after repair work, then this will practically not correct the situation, a significant part of the volume will not change.
The fluid must be changed completely. The sequence and features of replacing brake fluid, for example, when pumping with a running engine, depends on the design of the brake system (type of amplifier, the presence of anti-lock brakes, etc.). This information can be found in the vehicle owner's manual.
On domestically produced cars, the brake fluid is replaced as follows:
Method 1. The old fluid is completely drained by opening all the air release valves (fittings) from the hydraulic brake actuator. Then the reservoir is filled with new fluid and, pressing the brake pedal, pump it into the system. In this case, the valves must be sequentially closed when liquid appears from them. Then you need to remove air from each circuit of the hydraulic drive ("bleeding" the brakes). When using this method, the new fluid does not mix with the old one. Part of the new fluid released during pumping can be used again, having previously allowed it to settle and filtering.
Note. Before replacing, a discharge hose is put on each valve, the other end of which is lowered into a suitable container. Thus, it is possible to prevent damage to tires and paintwork on suspension parts, brakes by escaping brake fluid.
Method 2. Constantly adding fresh fluid to the master cylinder reservoir, each circuit is pumped in turn, thus displacing the old fluid and preventing the system as a whole from draining. This is done until new fluid appears from the valve. The advantage of this method is that air does not enter the hydraulic drive, which makes control pumping unnecessary. But at the same time, it is not excluded that a part of the old fluid will remain in the system. In addition, a larger amount of fresh fluid will be required than with the first method, since most of it removed from the hydraulic drive mixes with the old one and becomes unusable for further use.
SAFETY PRECAUTIONS FOR HANDLING BRAKE FLUID
Any brake fluid, regardless of type, is stored only in sealed containers, without contact with air, to prevent its oxidation, moisture build-up and evaporation.
Remember that brake fluid is usually flammable or flammable. It is strictly forbidden to smoke while working with it. It is poisonous, if ingested, even 100 ml, can be fatal. Usually, brake fluid smells like alcohol and can be easily confused with alcoholic beverage. If you accidentally swallow liquids, for example when pumping out of the master cylinder reservoir, you should immediately flush the stomach. In case of contact with eyes, rinse with plenty of water. In any case, in such situations, you need to see a doctor.
