Brake fluid is part of the hydraulic brake system. This is a working fluid that transfers pressure from the main brake cylinder to the wheel cylinders.

That is, a liquid conducts pressure in much the same way as wires conduct an electric current. And since the wires are not made from the first material that comes across, but from the one that is suitable, the liquid must have certain properties in order to be a good conductor of pressure in the car's braking system.

The main properties of brake fluid when working in brake systems:

- the brake fluid must remain liquid, that is, it must not boil or freeze under operating conditions;

the working temperature of the brake fluid ranges from -50 (in severe frost) to + 150 with dynamic acceleration. If the brake fluid boils, vapor bubbles displace some of it into the expansion tank of the GTZ and into the pipeline system. A liquid remains in the system, mixed with vapor bubbles. But if the liquid itself is incompressible, then microscopic gas bubbles are easily compressed. In the presence of gas in the brake system, the transmitted pressure will first of all go to compress the bubbles in their entire total volume, and only after that the pressure will be transferred to the liquid. With this outcome, the brake pedal will become soft, there will be no sharp increase in force, and the braking will be ineffective.

- brake fluid must retain its properties for a long time;

according to the regulations for the operation of cars, the brake fluid must be replaced every 12 months or more, all this time the brake fluid must be ready for operation in emergency situations.

also, moisture affects the boiling point of the brake fluid, and with an increase in the concentration of water, the boiling point decreases. All this is due to the constant volume of dissolved gas in the water and the boiling of water at 100 degrees Celsius, a temperature much lower than the upper limit of the operating temperature of the brake fluid. Therefore, the brake fluid must have a minimum hygroscopicity (moisture absorption). Moisture in the system contributes to corrosion of brake cylinders and pistons, and in cold weather, hydration plugs, obstruction of pipelines and, as a result, failure of the braking system are possible. In addition, at low temperatures, even if the brake fluid is not frozen, viscosity becomes a critical parameter - if it increases, the brake response time will noticeably increase. So, in particular, the standard developed by the International Association of Transport Engineers (SAE) explicitly states that the viscosity of brake fluid at -40 ° C should not exceed 1800 cSt (mm2 / s). In addition to the SAE, the requirements for brake fluids are reflected in the regulations of the US Department of Transportation. Federal Society for Vehicle Safety - U.S. Department of transprotation. Federal motor carrier safety administration. They have three regulatory classes: DOT-3, DOT-4, and DOT-5.1. but more on that later.

The graph shows the dependence of the boiling point of the brake fluid ROS on the volumetric water content.

- do not react with rubber goods - rubber technical products that play the role of seals in the brake system;

When the rubber swells, changes in the shape and properties of the rubber may lead to breaks, gaps in the seals (rubber rings) and pipelines (rubber hoses), leading to failure of the brakes.

Lubricate mechanically rubbing vapors to increase service life and prevent scuffing and excessive wear.

The lubricating properties of the fluid ensure the longest and most reliable operation of mechanical brake systems.

Considering such difficult requirements, modern brake fluid is quite complex in composition.

Basic compounds used in brake fluids

Glycol is the basis for brake fluid

Most modern products (including Neva, Tom and Rosa) are based on glycol mixtures. Glycols (aka diols) are alcohols with two hydroxyl OH groups. The simplest member of the glycol family is the well-known ethylene glycol used in the production of antifreeze and antifreeze.

Butyl alcohol + oil - base for brake fluid

Several decades ago, BSK appeared - red brake fluid. It is made from butyl alcohol and castor oil, mixing them in a 1: 1 ratio (hence the name of the brake fluid - BSK). Today this is history, since the properties that BSK provides are far from modern requirements for brake fluids. The main disadvantage is the low boiling point - only 115оС. In addition, the increased viscosity of BSK at subzero temperatures. The only significant plus of this brake fluid is that BSK does not absorb water.

Glycol ether + polyester - brake fluid base

Brake fluid Neva is based on glycol ether mixed with polyester. An important ingredient in this fluid is an anti-corrosion additive. This liquid is highly hygroscopic and rapidly lowers the boiling point during use. Today this liquid is considered obsolete and is not produced.

Figure 1 brake fluids DOT-3, DOT-4, DOT-5.1

Tom - this liquid also includes glycol ether and a package of targeted additives.
Tomi has improved basic performance indicators in comparison with Neva. Therefore, it is ranked as a class that meets the requirements of DOT-3.

The best brake fluid of domestic production

The most perfect mass product of the domestic glycol family is Rosa. This fluid is based on boron-containing polyester with a special additive package. Therefore, it meets the DOT-4 class regulations.
DOT-4 dew is fully suitable for use in the braking system of a modern car.

Highest brake fluid standard DOT 5.1

DOT 5.1 brake fluid is hygroscopic, does not provoke corrosion and lasts longer than DOT-3, DOT-4 brake fluids having a glycol base. The only drawback of this brake fluid is its low prevalence and high price.

Brake fluid parameters depending on standards.

Brake fluid	Manufacturer	Normative document according to which the brake fluid is manufactured	DOT-3 class. Dry / humid boiling point as per standard (+205 / + 140)	Class by DOT-4 Standard Dry / Wet Boiling Temperature Standard (+230 /+ 155)	DOT-5.1 class. Dry / humid boiling point as standard (+260 / + 180)	dry boiling temperature	"Wet" boiling temperature
BSK	no information	no information	does not match	does not match	does not match	115	no info
"Neva"	no information	no information	does not match	does not match	does not match	195	138
"Tom"	JSC "KHIMPROM", Kemerovo	TU 2451-076-05757618-2000	corresponds to	does not match	does not match	220	150
"Dew"	NPP "MACROMER", Vladimir	TU 2451-354-10488057-99		corresponds to	does not match	260	165
ROSDOT	LLC "TOSOL-SINTEZ" Dzerzhinsk	TU 2451-004-36732629-99	performance properties are higher	corresponds to	does not match	260	165
HYDRAULAN 408	BASF Germany	TTM 1.97.0738-2000	performance properties are higher	corresponds to	does not match	no info	no info
DOT-4	LLC Lukoil-Permnefte- rgsintez "Perm	TU 2332-108-00148636-2000	performance properties are higher	corresponds to	does not match	230	160
TORSA DOT-4	CJSC "BULGAR-SINTEZ" and CJSC "Bulgar Lada Plus", Kazan	TU 2332-001-49254410-2000	performance properties are higher	corresponds to	does not match	230	160

BRAKE FLUIDS used in VAZ cars

Since 1970, the clutch and brake systems of VAZ cars have been filled with "NEVA" brake fluid with a boiling point of 195 ° C. In 1983, the "TOM" brake fluid with a boiling point of 215 ° C was introduced, and in 1988 the "ROSA" brake fluid with a boiling point of 260 ° C was introduced. Since all these liquids are hygroscopic, during operation, their boiling point decreases, reaching the limits that are dangerous from the point of view of the formation of vapor locks in the brake system. Such limiting values ​​of the boiling point for TZ "NEVA" can be reached after one year of operation, for TZ "TOM" in two years, and for TZ "ROSA" in three years.
For this reason, AVTOVAZ excluded from the technical documentation the use of TZH "NEVA", limited the use of TZH "TOM" to cars of the VAZ-2101 ... VAZ-2107 and VAZ-2121, VAZ-21213 models.
The technical requirements for brake fluids such as DOT-3 and DOT-4 are set out in TTM 1.97.0738-2000. TTM applies to brake fluids intended for hydraulic brake and clutch systems of VAZ cars of various models.

You can mix DOT 3, DOT 4 and DOT 5 without silicone base. All of the following brake fluids are compatible and miscible with each other.

1. ROSDOT LLC "TOSOL-SINTEZ" Dzerzhinsk TU 2451-004-36732629-99
2. ROSA DOT-4 NPP "MACROMER", Vladimir TU 2451-354-10488057-99
3. TORSA DOT-4 CJSC "BULGAR-SINTEZ" and CJSC "Bulgar Lada Plus" Kazan TU 2332-001-49254410-2000
4. ROSA-DOT-3 NPP "MACROMER", Vladimir TU 2451-333-10488057-97
5. VOLUME JSC "KHIMPROM" Kemerovo TU 2451-076-05757618-2000
6. DOT-4 LLC Lukoil-Permnefteorgsintez, Perm TU 2332-108-00148636-2000
7. HYDRAULAN 408 DOT-4 Firm BASF Germany ТТМ 1.97.0738-2000
8. MOTUL Hydraulic DOT 5 (based on silicone free polyglycols).

Do not mix the above brake fluids with LHM and DOT 5 silicone base.

That is, in other words, you can mix mineral with mineral, silicone with silicone and non-silicone based on polyglycols with similar brake fluids, so look on the bottle and carefully read the name of the brake fluid base and then just add it to the brake system.

Brake fluid used for braking systems with ABS

For brake systems with ABS, there are no specialized brake fluids and standard fluids with improved performance properties are used for them, that is, DOT-4 or DOT-5.1.

Requirements for compliance with safety measures when working with brake fluids

Store the product in a tightly closed container without moisture.
Aggressive towards varnishes, paints and leather.
In case of contact with skin, wash off with water.

Terms of operation and replacement of brake fluid

Replacement is done once every 12 or 24 months in accordance with the recommendations of the designers. AvtoVAZ regulates the terms - in two years or after 100 thousand kilometers.

Standards for brake fluid for vehicles.

Unfortunately, Russia has lost its weight in the world and the relevance of using internal standards for many industrial, technological procedures and regulations. At the moment, GOSTs are only advisory in nature, and anyone can issue TU, register with the standardization center and work on it. In this regard, in the Russian market of brake fluids, the American DOT standard (from the English Department of transport) is actively used, nothing more than the standard of the US Department of Transport, this organization was mentioned earlier. It is the Standard No. 116 for brake fluid designed for self-propelled vehicles that is currently the most popular and demanded when choosing a brake fluid.

Before filling the brake system with fluid, it is necessary to thoroughly clean the master cylinder and bypass valves on the wheel cylinders of the brakes and the hydraulic vacuum booster from dirt, check and adjust the clearances between the pusher and the piston of the master cylinder, as well as between the pads and brake drums.

The brake system only needs to be filled with special brake fluid. Mixing brake fluids of different brands is not allowed. It is strictly forbidden to add to the system, even in the smallest quantities, mineral oils, gasoline, kerosene or mixtures that cause destruction of the rubber parts of the brake system.

How to pour alcohol into the brake system

In the absence of a special brake fluid, a mixture consisting of 50% (by weight) castor oil and 50% butyl alcohol can be poured into the system. Butyl alcohol can be replaced with isobutyl or ethyl alcohol, but keep in mind that ethyl alcohol evaporates more easily and the mixture can change quickly, especially in hot weather or with prolonged use of the brakes.

You can not replace castor oil with glycerin, as its viscosity increases greatly with decreasing temperature.

If a different type of brake fluid is poured into the system, then it is necessary to remove the old fluid from it and thoroughly flush the entire brake system with alcohol, acetone or new fluid. When pouring brake fluid into the system, the maximum cleanliness must be observed, since if dirt enters the system, the brakes will fail.

To fill the system and remove air from it, proceed as follows:

1. Unscrew the filler plug of the master cylinder and fill the cylinder with brake fluid.
2. Remove the rubber protective cap of the bypass valve of the wheel cylinder of the right rear brake and replace it with a rubber hose, the other end of which is immersed in the brake fluid, poured halfway into a glass vessel with a capacity of at least 0.5 liters.
3. Unscrew the bypass valve by 1/2 ... 1/4 turn, then press the brake pedal several times. Step on the pedal quickly and release slowly. In this case, the liquid from the master cylinder fills the system and displaces air from it, which comes out through the bypass valve, the hose and through the liquid into the vessel in the form of bubbles. During pumping, it is necessary to add liquid to the master cylinder, preventing the bottom from being exposed in its reservoir.
4. After the air exit from the system stops (the bubbles from the hose lowered into the glass vessel stop), it is necessary to tighten the bypass valve tightly with the pedal depressed, remove the hose from the bypass valve and put a protective cap on it.
5. Bleed the brake system in the same way in the following sequence: front right brake, front left brake, rear left brake, hydraulic booster cylinder (through two bypass valves).
6. After bleeding the brake system, add fluid to the master cylinder so that its level is 15-20 mm below the upper edge of the filler hole, and tighten the master cylinder plug tightly.

Before installing the plug, blow air through the vent hole.
If all brakes and actuator are correctly adjusted and there is no air in the system, then the brake pedal should not be depressed more than half the stroke when pressed, after which the pedal should feel "stiff". Lowering the pedal more than half the stroke indicates large gaps between the brake pads and drums.

If the resistance of the pedal is insignificant, it can be squeezed almost to the stop on the floor of the cab (“soft” pedal), this indicates that there is air in the system. In this case, it is necessary to continue pumping until the air is completely removed.

Do not press the brake pedal if at least one drum is removed, since the pistons will be squeezed out of the wheel cylinder under the fluid pressure and the fluid will flow out.

The fluid used to bleed the brakes can be reused, allowing it to settle until air bubbles are removed.

Bleeding the system must be carried out not only when filling the brake system with fluid, but also when disconnecting any part of the hydraulic system for repair or replacement, i.e. when air can somehow enter the system.

The brake pedal usually falls into the floor at the most inopportune moment. When brakes are especially needed

Science

Real stories about how they managed to get out of such a difficult situation are almost never heard among the drivers: not being able to stop, it is difficult to survive on a mountain serpentine or in front of an obstacle that "rolls" at a speed of two hundred ... And those who are lucky often talk about miracle: absolutely serviceable brakes with worn-out friction surfaces (pads, discs, drums) failed. The pedal "suddenly" failed, and after a while "recovered". It was really possible to believe in evil fate, if not for one detail, more precisely - liquid. Brake, of course.

In the brakes, it plays no less role than any other part of the system. Their performance depends on its condition, and hence the lives of people.

When heated, any liquid begins to boil, that is, it moves from one state of aggregation to another. Gas, unlike liquid, is easily compressed. There is plenty of heat in the brakes: with frequent harsh braking, the brake pads heat up to almost a thousand degrees. When the fluid in the hydraulic brake drive boils, its vapors (i.e., the gas phase) are easily compressed, the pedal goes to the floor. This problem was known at the dawn of motoring and since then, with the growth of power and speed, it has been regularly successfully solved. Each time, chemists find a new compound that does not freeze at low temperatures and does not boil at relatively high temperatures.

The last three generations of hydraulic brake fluid (DOT-3, DOT-4 and DOT-5.1) are produced on a glycol basis. They are all good, one problem: they actively absorb water from the air. The boiling point of the liquid gradually decreases, reaching the maximum permissible (150 ° C). Almost all car manufacturers recommend replacing the GTZ every two years or 60 thousand kilometers. Its further use is fraught with danger.

"Thrifty" car owners justify themselves by the fact that they do not drive fast, and that they do not go to the mountains at all. But the water in the hydraulic drive not only boils, but also freezes and also causes corrosion. Most likely, it will not come to the complete freezing of the liquid, but the braking efficiency may deteriorate. And the most unpleasant thing is that "wet" brake fluid loses the stability of its physical properties, which affects the stability of the brakes. At the beginning of the trip, the pedal “stands like a stake”, and after several vigorous braking, it suddenly becomes “sluggish”. There is no need to talk about cost savings, even if the accident was avoided.

Brake pipes today are mostly made of steel. With the old liquid, despite the presence of a protective coating, they rust not only on the outside, but also on the inside. And who knows if corrosion centers will appear soon? Moreover, designers, believing that their recommendations are unconditionally followed, often use materials that are incompatible in aggressive environments. A typical example is aluminum pistons in cast iron brake cylinders. A little moisture, and the pistons became acidic, lost their mobility due to corrosion. A bottle of fresh brake fluid costs no more than one cylinder. How many of them are there by car? Let's add pipes and work. Are you so rich that you can afford not to change your fluid for years?

On practice

We brought a small red suitcase with the TRW logo from Frankfurt from the Automechanika-2008 exhibition. It contains an electronic device for testing brake fluid (YMB 214). The instruction is in 19 languages, but without Russian. In the near future, the device will be available in Moscow, and then a Russian page will appear. However, you can do without it. Working with the device basically boils down to three steps: correctly connect the clamps to the battery, put the device's "trunk" into the tank with liquid and read the readings on the scale. Let's try to find out how safe the cars around us are.

Battle check

The cavalry swoop with appalling conclusions failed. It can be seen that the target for the attack was poorly chosen. The motor transport company, which is part of the largest and oldest communications company since Soviet times, we admit, was a pleasant surprise. The head of the workshop, having examined the outlandish device, sighed: “Sometimes they don’t give us money for spare parts either. We orient ourselves by the color of the brake. " Our conclusion: there are no color blind people at the car depot.

All tested cars were filled with conditional brake fluid. The temperature of all samples ranged from 180 to 210 ° C. Recall that the critical values ​​are 140 ° C for DOT-3, 150 ° C for DOT-4 and 180 ° C for DOT-5. GTZh DOT-4 is used in "Gazelles", "Volgas" and "fours", which make up the majority of the park. Excellent result!

We go out into the street, right in front of the editorial office. The one-year-old Sobol takes the lead: 253 ° С. However, lower values ​​would be somewhat scandalous. The Volvo 940, released in the last century, was approached not without sarcasm, and unsuccessful attempts to unscrew the cap of the brake master cylinder reservoir caused frank laughter from those present. It is not surprising that the cork did not go without a rag: for two years of owning a car, its owner did not even check the liquid level. The result was shocking - 193 ° С for the liquid, which served much more than it should have! And this is in St. Petersburg, "famous" for its swamp climate and the corresponding air humidity.

The third day of testing was carried out in a garage cooperative. And not in vain. Only here were cars with "criminal" brake fluid found. The worst result (127 ° C) was recorded in the fifteen-year-old "Niva", abandoned by the owner in the garage as unnecessary a couple of years ago. During its operation, the owner changed the complete calipers and regularly poured brake fluid, but when he did it, he could not remember. In several machines, the boiling point of the liquid was close to critical. But it was not possible to identify obvious patterns: both old domestic cars and foreign cars “sinned”.

Our test does not pretend either to be scientific or to be completely objective. We were able to persuade less than a hundred car owners to check the GTZ. And a negative result was revealed only in isolated cases. More accurate data could be given by service station specialists armed with a similar tester. Our observations only confirm the fact that the problem really exists, although, perhaps, it is somewhat exaggerated. At least in terms of service life.
However, in the absence of a device and the skill of "diagnosing by eye", the recommendations of the factory management should not be neglected.

TRW YMB 214

The device is specially designed for the needs of service companies involved in the repair and maintenance of brakes. It allows you to determine the state of the used brake fluid in the reservoir of the master brake cylinder. Power supply - from the car battery (12 V).

The use of the device allows replacing the GTZh on time, preventing the development of internal corrosion and failure of the brakes, both due to liquid boiling and due to malfunction of cylinders and pipelines. In the process of replacing the fluid, other defects can be identified, the elimination of which is useful to the owner who receives a guaranteed serviceable car from the repair, and is beneficial to the service, since it gives additional workload to the workers.

Car for pumping

Replacing brake fluid is not much different from bleeding the brakes. Hoses are put on all pumping fittings, the other ends of which are lowered into transparent containers. The fittings open all at the same time. We squeeze out the old fluid from the system, sharply pressing and smoothly releasing the brake pedal. Pour the spilled liquid into another container. It can be useful for loosening tight, rusty nuts.

Put the containers under the hoses again, pour fresh liquid into the tank and swing the pedal in the same rhythm until the liquid appears in the vessels. We wrap all the fittings and bleed the brakes in the sequence indicated in the instruction manual. It is better not to use fresh drained liquid for its intended purpose.

A bike with a commentary

In the seventies, such a bike went among the Leningrad taxi drivers. The taxi driver drove to the full, hurrying with the passenger to the airport. I wanted to slip into yellow (after green), but the car in front stopped. Taxi driver on the brakes, the pedal fails. Impact, accident.

The taxi driver sat in the car, holding the pedal “on the floor”, for two hours, until the traffic police inspector arrived. Only after the fact of the failure of the brakes was recorded in the protocol, he removed from the pedal, not numb, but a stiff leg. The next time the brakes were pressed, they worked normally. An incomprehensible factory defect was recognized as the cause of the accident. But most likely it was in the old or low-quality brake fluid. The resourceful (and patient) driver escaped punishment. The taxi company paid for the wrecked car. Whether the claim was made to GAZ, history is silent.

It makes no sense to repeat the "feat of a taxi driver" on your car: the owner himself bears responsibility for its technical condition. The only exception is a completely new car. For a factory defect, there is a chance to bring the manufacturer to justice.

It is another matter if you are a hired driver and you have been driving a car that has got into an accident recently. Then, perhaps, it will be possible to transfer the arrows to the owner. But in any case, it is cheaper and less troublesome to replace the liquid on time.

When no fluid leaks in the hydraulic brake drive, it would seem that you don't need to pay attention to it. However, the braking efficiency and the stability of the system depend on its state. If, for example, poor antifreeze or engine oil only shortens the life of the engine, then poor quality brake fluid can lead to an accident.

General information

Brake fluid (TF) consists of a base (its share is 93-98%) and various additives (the remaining 7-2%).

Obsolete liquids, for example "BSK", are made on a mixture of castor oil and butyl alcohol in a 1: 1 ratio. The basis of modern, the most common, including domestic ("Neva", "Tom" and RosDOT, aka "Rosa"), are polyglycols and their ethers 1 . Much less commonly used silicones 2 .

In the complex of additives, some of them prevent the oxidation of TF by atmospheric oxygen and under strong heating, while others protect metal parts of hydraulic systems from corrosion.

Basic properties any brake fluid depends on the combination of its components.

• Boiling temperature. The higher it is, the less the likelihood of a vapor lock in the system. When the vehicle is braking, the working cylinders and the fluid in them heat up. If the temperature exceeds the permissible value, the TZ will boil and vapor bubbles will form. The incompressible fluid will become "soft", the pedal will "fail" and the machine will not stop in time.
• The faster the car went, the more heat will be generated during braking. And the more intensive the deceleration, the less time will be left for cooling the wheel cylinders and feed pipes. This is typical for frequent prolonged braking, for example in mountainous areas and even on a flat highway, loaded with traffic, with a sharp "sporty" driving style.

The sudden boiling of TZ is insidious in that the driver cannot predict this moment.

• Viscosity characterizes the ability of the fluid to be pumped through the system. The temperature of the environment and the TZ itself can be from minus 40 ° C in winter in an unheated garage (or on the street) to 100 ° C in the summer in the engine compartment (in the master cylinder and its reservoir), and even up to 200 ° C with intensive deceleration of the car ( in the working cylinders). Under these conditions, the change in the viscosity of the fluid must correspond to the flow sections and clearances in the parts and assemblies of the hydraulic system specified by the vehicle designers.

Frozen (all or in some places) TJ can block the operation of the system, thick - it will be difficult to pump through it, increasing the response time of the brakes. And too liquid - increases the likelihood of leaks.

• Impact on rubber parts. Seals should not swell in TZ, reduce their size (shrink), lose elasticity and strength more than is permissible.

Swollen cuffs make it difficult for the pistons to move back in the cylinders, so the vehicle may slow down. With seated seals, the system will be leaky due to leaks, and deceleration will be ineffective (when the pedal is depressed, the fluid flows inside the master cylinder, not transferring force to the brake pads).

• Impact on metals... Parts made of steel, cast iron and aluminum should not corrode in the TJ. Otherwise, the pistons will "sour" or the cuffs working on the damaged surface will quickly wear out, and the fluid will flow out of the cylinders or will be pumped inside them. In any case, the hydraulic drive stops working.
• Lubricating properties. In order for the cylinders, pistons and cuffs of the system to wear less, the brake fluid must lubricate their working surfaces. Scratches on the mirror of the cylinders provoke TJ leaks.
• Stability- resistance to high temperatures and oxidation by atmospheric oxygen, which occurs faster in a heated liquid. The oxidation products of the tAs corrode metals.
• Hygroscopicity- the tendency of polyglycol-based brake fluids to absorb water from the atmosphere. In operation - mainly through the expansion hole in the tank lid.

The more water is dissolved in the TH, the earlier it boils, thickens more strongly at low temperatures, lubricates parts worse, and the metals in it corrode faster.

Brake fluid classes

In Russia, there is no single state or industry standard governing the quality indicators of brake fluids. Domestic manufacturers work according to their own specifications, focusing on the norms adopted in the USA and Western Europe (standards 3 J1703, ISO (DIN) 4925 and FM VSS N116). Liquids are classified according to boiling point and viscosity, the rest of their properties are similar.

Which TJ should be used in the car is decided by the manufacturer. As a rule, fluids of class DOT 3 are intended for relatively slow-moving machines with all drum brakes or disc brakes in front. TZ with improved operational characteristics, corresponding to the requirements of DOT 4, are designed for modern cars with increased dynamic qualities. Such cars allow frequent sharp accelerations and intense decelerations, and they have predominantly disc brakes on all wheels. DOT 5 fluids are rarely used, mainly on road sports cars. Thermal loads on TJ are commensurate with those arising in the hydraulic systems of special racing cars.

Liquids "BSK" and "Neva" (grades A and B) do not meet modern requirements for boiling points, and "BSK" also does not meet low-temperature properties. It freezes already at minus 20 ° C.
Features of the operation of brake fluids

The absorption of water from the atmosphere is characteristic of polyglycol-based TA. At the same time, their boiling point decreases. FM VSS standardizes it only for "dry", not yet absorbed moisture, and humid, containing 3.5% water, liquids - ie. limits only limit values. The intensity of the absorption process is not regulated. TG can be saturated with moisture at first actively, and then more slowly. Or vice versa. But even if the boiling point values ​​for "dry" liquids of different classes are made close, for example, to DOT 5, when they are moistened, this parameter will return to the level characteristic of each class. However, in laboratory tests, TJ manufacturers, as a rule, build curves of the boiling point change. They are different for each liquid.

TG needs to be replaced periodically, without waiting for its condition to approach a dangerous limit. The service life of the fluid is assigned by the car plant, having checked its characteristics in relation to the features of the hydraulic systems of its cars.

Checking the condition of the liquid. It is possible to objectively determine the main parameters of TAs only in the laboratory. In operation - only indirectly and not all.

The liquid is independently checked visually - in appearance. It should be transparent, homogeneous, without sediment. In addition, in car services (mainly large, well-equipped, servicing foreign cars), its boiling point is assessed with special indicators. Since the fluid does not circulate in the system, its properties may differ in the tank (test location) and in the wheel cylinders. In the reservoir, it is in contact with the atmosphere, gaining moisture, but not in the brakes. On the other hand, the liquid there often and strongly heats up, and its stability deteriorates.

However, even such tentative checks should not be neglected, there are no other operational control methods.

Compatibility. TAs with different bases are incompatible with each other, they stratify, sometimes a precipitate appears. The parameters of this mixture will be lower than that of any of the original fluids, and its effect on rubber parts is unpredictable.

The manufacturer, as a rule, indicates the basis of TJ on the packaging. Russian RosDOT, Neva, Tom, as well as other domestic and imported polyglycolic liquids DOT 3, DOT 4 and DOT 5.1, can be mixed in any proportions. TJ class DOT 5 are based on silicone and are incompatible with other 4. Therefore, FM VSS 116 requires "silicone" fluids to be dyed dark red. The rest of modern TJs are usually yellow (shades from light yellow to light brown).

For additional verification, you can mix liquids in a 1: 1 ratio in a glass container. If the mixture is clear and there is no sediment, the TAs are compatible.

Replacement. The addition of fresh fluid when pumping the system after repair does not restore the properties of the TJ, since almost half of it practically does not change. Therefore, within the time frame set by the car plant, the fluid in the hydraulic system must be completely replaced. The sequence and features of this operation, for example, bleeding with a running engine, depend on the design of the system (such as an amplifier, anti-lock devices, etc.) and are known to specialists of service stations. Often this information is in the vehicle manual.

On domestic cars, the fluid is replaced in one of the following two ways.

• The old TJ is completely drained by opening all the air release valves (fittings) and draining the system. Then the tank is filled with fresh liquid and pumped in by depressing the pedal. The valves are sequentially closed when TZ appears from them. Then air is removed from each circuit (branch) of the hydraulic drive.
• The disadvantage of this technique is the need for the final (control) pumping of the system. In addition, a discharge hose must be put on each valve by lowering its other end into a suitable container5 - the leaking TJ can damage tires and paint on suspension parts, brakes, wheels. But the new liquid is guaranteed not to mix with the old one, and part of the fresh TZ released during pumping, having allowed it to settle to remove air and filtered, can be used again.
• The replaceable TJ is displaced with a fresh one, constantly refilling it into the tank of the master cylinder and preventing the system from draining. For this, each circuit is pumped in turn until fresh liquid appears from the valve.
• In this case, air does not enter the hydraulic drive, but it is possible that some of the old TJ will remain in it, since it is difficult for an inexperienced person to distinguish it from a new one. In addition, more fluid is needed than when pumping in the previous way. Part of it released from the system is mixed with the old and unusable.

Safety measures when working with TJ

You need to store any liquid only in a hermetically sealed container so that it does not come into contact with air, does not oxidize and does not absorb moisture from it or evaporate.

A WARNING

In hydraulic systems, rubber seals based on natural and synthetic rubber are used. The latter can withstand high temperatures well, but such rubber is destroyed by mineral oils, gasoline and kerosene. Therefore, when repairing system components, flush or lubricate the cuffs, and even metal parts, you need only fresh clean brake fluid.

• Brake fluids "Neva", "Tom" and RosDOT are flammable, and "BSK" is flammable. Smoking while working with them is prohibited.
• TG is poisonous - even 100 cm3 of it, if it gets inside the body (some liquids smell like alcohol and can be mistaken for an alcoholic drink), can lead to the death of a person. In the case of ingestion of TJ, for example, when trying to pump out part of it from the reservoir of the master cylinder, you must immediately induce vomiting (see our help). If liquid gets into eyes, rinse with water jet. And in any case, see a doctor.

OUR REFERENCE

You can induce vomiting by drinking (optional):

• as much water as the body will accept (usually 2-2.5 liters);
• 3-4 glasses of soapy water;
• a glass of warm water, in which a teaspoon of dry mustard is diluted.

• You need to choose a TJ recommended by the car factory.
• Liquid packaging must be airtight. When lightly squeezed from the sides, it springs.
• The membrane under the lid is preferable from foil - this does not allow water to pass through and indicates the reliability of the manufacturer.

The editors would like to thank Ph.D. E. M. Vizhankova and senior researcher GI Matrosov, specialists of the 25th State Research Institute of the Ministry of Defense of Russia, for their help in preparing the material.

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1 Polyglycols and their ethers are a group of chemical compounds based on polyhydric alcohols. They have a high boiling point and good low temperature properties.
2 Silicon-organic polymer products. Their viscosity depends little on temperature, they are inert to various materials, they are efficient in the temperature range from minus 100 to 350 ° С.
3 SAE - Society of Automotive Engineers (USA), ISO (DIN) - International Organization for Standardization, FM VSS - Safety Precautions Act (USA).
4 Liquids of class DOT 5.1 that do not contain silicone are sometimes referred to as DOT 5.1 NSBBF, and silicone DOT 5 - DOT 5 SBBF. NSBBF stands for non silicon based brake fluids and SBBF stands for silicon based brake fluids.
5 The same should be done when removing air from the system or its circuit. In addition to damage to parts, fluid escaping from the valve under pressure can splash into the eyes.

Based on site materials www.zr.ru

Brake fluid is a type of hydraulic fluid that is used in hydraulic braking systems and hydraulic clutch systems on automobiles, motorcycles, light trucks, and bicycles. The fluid is used to transmit pressure and to enhance the braking force.

General information about brake fluid

The principle of operation of brake fluid is its low compressibility. Molecules do not have an internal void, therefore, when compressed, the volume of the liquid does not decrease, and the pressure quickly spreads to the entire volume.

Brake fluid composition

There are different types of brake fluid, but it is usually made from a low-viscosity solvent such as alcohol and a viscous non-volatile substance such as glycerin.

On the basis of polyethylene glycol, brake fluid is produced under the brands DOT 3, DOT 4 and DOT 5.1.

Silicone-based - silicone-organic polymer products DOT 5 brand.

For vehicles with anti-lock braking system, DOT 5.1 / ABS brand brake fluids based on silicone and glycols can be used. About brake fluids wiki: link.

Characteristics and properties of brake fluid

In order for the braking system to function properly, the brake fluid must have certain characteristics and meet quality standards.

Boiling temperature... New brake fluid does not contain moisture, so its boiling point is within acceptable limits. But over time, moisture from the ambient air enters the fluid, usually 1-2% per year of the total volume, but the characteristics of the brake fluid begin to change.

During braking, the working fluid heats up to very high temperatures due to friction. At this point, it is very important that the brake fluid does not boil, since in this case moisture evaporates from the fluid in the form of vapor. And steam is dangerous in that it is easily compressed and during the next braking the pressure on the brakes will be less, since part of the volume will be taken away by the compressed steam.

The boiling point of brake fluid directly depends on the amount of water in it. The more water, the lower the boiling point and the greater the chance of "losing" the brakes.

Hygroscopicity... Some brands of "brake" have minimal hygroscopicity (moisture absorption), for example, DOT 5 and can maintain the required characteristics throughout the entire service life. But the most common brands DOT 3, DOT 4 and DOT 5.1 are gradually losing their properties due to the increasing amount of moisture in them.

Viscosity... This characteristic will determine how the brake fluid will be pumped throughout the system. And it should pump well both at -30 degrees Celsius and at 200 degrees during braking.

If the fluid freezes completely or in places, it will block the brakes. Too thick fluid will be difficult to pump throughout the system, which will lead to either poor braking or different effort on different wheels. And too liquid will lead to leaks.

Corrosion protection... The brake fluid itself acts as a corrosion protection inside the brake system. In this case, protection must be provided even with small amounts of moisture inside the system.

Corrosion protection is provided by special additives. They also provide protection for the sealing elements.

Compressibility... Ideally, the brake fluid should not compress at all, but there are certain tolerances for this characteristic. The main thing is that the liquid works equally well under different temperature conditions.

	"Dry" boiling point, ° C	"Wet" boiling point (water 3.5%), ° C	Viscosity, mm 2 / s	Main components
DOT 2	190	140	—	Castor oil / alcohol
DOT 3	205	140	1500	Glycol
DOT 4	230	155	1800	Glycol / Boric acid
LHM +	249	249	1200	Mineral oil
DOT 5	260	180	900	Silicone
DOT 5.1	260	180	900	Glycol / Boric acid

Brake fluid compatibility

For topping up, you can use a liquid from the same manufacturer, but subject to the principles:

• You can only add liquid with a higher rating figure, that is, DOT 4 can be poured into DOT 4, and DOT 5.1 can be poured into DOT 4.
• Do not mix DOT 5 with other brands - DOT 3, DOT 4, DOT 5.1.
• Mineral (eg LHM +) and glycolic fluids must not be mixed.

If you break the rules, this will lead to a serious change in the characteristics of the liquid for the worse.

How often to change the brake fluid

The question of when to change the brake fluid can be answered unequivocally: once every two years or after 40,000 mileage. These are general guidelines.

If the car is operated in harsh conditions, then it is necessary to change the brake fluid more often.

Regular topping up cannot fully compensate for changes in the properties of the liquid - the boiling point drops, the chemical composition changes, and anti-corrosion additives work worse. You can use the refilling method only when carrying out repairs or in the event of a leak, when you just need to drive to a service station or garage.

You can determine an unusable brake fluid:

• With a complete analysis using special equipment.
• "By eye" - the old liquid is dark in color, while the new one is translucent.
• Using a device that determines the amount of moisture in a liquid. If less than 3.5 percent, then you can still ride.

It is necessary to fill the brake fluid into the expansion tank of the brake system. It is usually located above the brake master cylinder and serves to compensate for the heating of the brake fluid and to prevent air from entering the system.

The fluid level in the reservoir must be between the "MIN" and "MAX" marks. In modern cars, there is a float with a sensor that will alert the driver when the fluid level in the reservoir has dropped below the minimum mark.

How to change brake fluid

It is best to do this at a specialized service station. Most modern cars have an ABS system, and this leaves its mark on the procedure. Special equipment is required to pump the system with new fluid.

If you are told that you can perform a brake fluid change without bleeding without special equipment, then do not listen to these tips. Yes, on some wheels, the pressure from the reservoir can push the system through, but this will not work on all. As a result, air or old fluid will remain in the system. At the service station, the fluid is replaced under pressure, so subsequent pumping is not required.

The replacement procedure itself is as follows. New liquid is poured into the empty expansion tank of the cooling system, after which pumping occurs on each line, during which the new liquid displaces the old one.

The average volume of brake fluid is 0.75 to 1.3 liters.

A clear change of brake fluid without special equipment is described in the video below:

Brake fluid prices

Usually prices for DOT 4 brake fluid fluctuate around 600-700 rubles per 1 liter. Some manufacturers ask for 1,500 rubles for a similar brand.

DOT 5.1 costs from 1 100 rubles, depending on the manufacturer.

Security measures

To prevent the brake fluid from oxidizing, evaporating and absorbing moisture, it must be stored in an airtight container.

They are generally flammable and should be kept away from open flames and high temperatures.

In no case should you drink, even a small amount will lead to poisoning. In case of contact with eyes, rinse thoroughly with clean water and consult a doctor.