You already know the basic features of brake fluid. You know that this liquid must remain dry, must not boil and freeze. In the second part, we will look at each of the main parameters in detail.
Boiling
Typically, the boiling point is measured for "dry" and "wet" liquids separately. They do this in order to be able to build a temperature graph for the entire period of possible operation of the liquid. For the test, only 3.5% water is added to the liquid, but this is enough to project the absorption of water from the air. When a liquid is heated and cooled, its viscosity is measured, as a rule, an average temperature range from -40 to +100 degrees Celsius is taken for measurements. During this period, almost all modern standards fit: FMVSS No. 116, ISO 4925, SAE J1703 etc. In real conditions, the operating temperature of the TJ can reach limits from -50 to 150 degrees Celsius.
How noticeable will the liquid boil?
When heated and then boiled, gas bubbles will begin to form in the TJ. Part of the liquid will be squeezed into the reservoir of the master brake cylinder and gas will take its place. A gas plug will appear in the system. Anyone who has bled the brakes knows what it looks like for the driver. The brake pedal becomes soft and moves without any perceptible effort. Naturally, the car does not react to your actions and continues to drive as before.
Why does brake fluid boil?
Laziness, forgetfulness, water. Water throughout the rest of the text will be the main enemy, albeit indirect in relation to human recklessness.
The brake system of most cars has only 1000 ml of fluid. By adding 2% water to it, and this is no less than 20 ml of volume, we will lower the boiling point by 70 degrees. If we take, for example, DOT-4, then it will boil at 150-160 degrees. You can trust me. In the city, you won't notice it, but emergency braking on the highway ... sorry, there are no guarantees. It’s good if it’s winter and the TJ freezes. In this case, you will be able to find out about the problem in advance. The viscosity of the fluid will increase dramatically and it will be extremely difficult for you to wait for the brakes to work.
Frozen brake fluid?
The reason is the water. Not a timely replacement. “I haven’t changed it for five years and everything is fine” is an unnecessary and inappropriate philosophy.
But that's not all. Sufficiently harsh operating conditions of the TJ, its inevitable aging, leads to the fact that the components of the liquid begin to oxidize, while releasing not the most calm compounds. Shells and dents on the working surfaces of the elements of the brake system are not traces of any mechanical impact, but the results of chemical reactions. TJ oxidation products perfectly corrode metals. Moreover, the longest reaction test is only 120 hours at 100 degrees Celsius. So, under certain conditions, it will not even take a year for the car to require repair - expensive repairs.
After all of the above, you can probably not mention that water is rust, but, nevertheless, this is a fact.
How to avoid problems?
Yes, it's easy for the most part. The cost of servicing the brake system is acceptable in the vast majority of cases. I specifically do not write any prices, because times go by, prices change, and in this matter the problems are still the same as 30 years ago.
The operating rules are simple.
If you do not know something about the brake system of your car, change the fluid immediately after buying a car. Then repeat this every couple of years. Under normal conditions, more frequent replacement is not required.
Driving through puddles, etc. Through the cylinders of the brake system, water will not penetrate into the liquid, well, unless of course you park for the night on the rapids in the water. The main affected area is the tank and its lid. As we saw in the first part, there is a hole in the lid. Although it is not large, it is not designed for high pressure washing.
What else can speed up the fluid change. Damp areas of operation, large temperature fluctuations, which will inevitably cause condensation to form on the walls and lid of the tank. Some issues need to be approached individually.
How to assess the condition of the brake fluid?
No way! No. It is clear that it should be clean, transparent and without sediment ... but in most cases the tank itself will not let you find out, and even if you find it as such, it will not say anything about how much water it has already absorbed. Good people made an analyzer device with which you can find out everything about the state of the TJ, but the cost of the device is such that it not only makes no sense to buy it for personal use, but sometimes it will be cheaper to change the liquid than to pay the cost of such a test at the station. Although if they offer it for a small price, agree, it will definitely not be superfluous.
Peculiarities.
Brake fluid can only be mixed within a class, such as DOT-4.
Do not mix DOT-4 and DOT-5.
Adding fluid to the system. Let's do it. It only makes sense to add fluid to the system if it starts to go away on the road and you just need to get home. If the liquid leaves, then it is necessary to look for the cause as soon as possible, because. the brakes fail instantly, nothing can be guessed.
Top up - refresh. It's not an option at all. TJ does not restore its properties when adding fresh liquid. In this case, it's nothing more than a waste of money.
Store liquid only in an airtight container. Without air access, without temperature difference, without moisture access. With its range and cost, it is easier not to store. So. To buy on the road just in case, but it’s not worth it to carry it constantly in the trunk.
If you decide to work with TJ on your own, there are a few things you need to keep in mind.
Do not smoke while handling liquid. Forbidden. Dangerous.
TJ is poisonous. This is practically the most dangerous liquid in the car. In addition, she is aggressive. In case of contact with eyes, rinse with plenty of water and seek medical attention immediately.
If TA was swallowed. Induce vomiting immediately, by any means, and without delay, head to the nearest hospital. The fact that the legends say that it was drunk during Prohibition will not give you a chance. There is a complex way of cooking. In order to endanger the life of an adult, 100 milliliters of liquid is enough. And it is under threat with resuscitation and all that.
From subtleties.
When working with elements of brake systems, cuffs, anthers, seals - do not wash them with gasoline and kerosene. These rubber bands are made of pure rubber and are not able to withstand, without consequences, such a wash.
In conclusion, I would like to touch on one more point.
In Russia, there is no standard for the production of brake fluids. There is only a set of technical conditions, applying which everyone does what he wants. Well, or what happens. I do not recommend using domestic fluids in foreign systems. The statistics that come from experience are not comforting. Foreign cars are leaking on our brakes.
The requirements for brake fluid are quite serious - it should not accumulate water (condensate from the air) in itself, and also have a stable viscosity in the range from -60 to +300 degrees. Brake fluid must be neutral to cuffs, rubber bands and metal.
During prolonged or sudden braking, the brake pads become very hot, and this heat is transferred to the caliper piston, thereby the brake fluid can boil, forming vapor locks in the system, causing the brake pedal to become cottony or fail, and for effective braking it is necessary to pump up pressure by rapidly pressing the brake pedal. This problem is especially common on Gazelles, since the braking system of the car is not designed for the mass that they carry.
Brakes, like engine oils, are different, but they are united by the Dot3 or Dot4 model.
Dot 3- rather old brake fluid and the only plus, the cost is slightly lower than Dot4 and it can be mixed with DOT4. You can use such a fluid in cars in which the brake system is not loaded. Change this fluid every 2 years.
Modern cars in our climate zone use DOT4 and Dot 3 is no longer on sale. More advanced than DOT3, it has a number of advantages. The increased boiling point, the composition contains additives that absorb moisture and, accordingly, such a liquid freezes less at low temperatures. The cost of 1 liter is about 300 rubles. Change DOT4 brake fluid every 3 years.
Liquid DOT5 they are not used in our climate, since the composition includes silicone, which simply does not mix with water, and the condensate that accumulates in some recess simply freezes and blocks the passage of liquid through the line. DOT5 does not mix with DOT4 or DOT3.
Why you need to change your brake fluid.
Condensation gets into any fluid in a car, and brake fluid is no exception. Water reduces the properties of the brake fluid, it begins to freeze, boil, and such a fluid becomes aggressive to the metal, forming corrosion on the cylinders or pistons of the calipers. From severe corrosion of the caliper, a brake fluid leak occurs. Motorists who save on the timely replacement of brake fluid, in the future, doubly pay for the replacement of parts of the brake system, and this is at best.
How to change brake fluid
Brake fluid changes can be combined with seasonal wheel changes. You will need an 8mm or 10mm wrench and a short 5mm tubing and a liter of Dot4. In order not to break the edges we treat the bleed fittings, the joints with penetrating lubricant and then unscrew the end head with a snug fit, as unscrewed, you can also drain it with an open-end wrench
It is enough to pump out the old fluid from the tank with a syringe and fill in the new one. Then, at the far wheel, unscrew the bleeder valve and drain about 30 milliliters of liquid, and so on for each wheel. The last wheel should be the one closest to the brake fluid reservoir.
Volume brake fluid reservoir 0.5-0.8 liters, depending on the brand of car.
If brake fluid leaks- in fact, this is nothing to worry about, as the brake pads wear out, and the brake calipers extend more and the fluid level decreases. When installing new pads, the level will return to normal. As a rule, at a low level of brake fluid, a flashing handbrake lamp signals.
Replacing the brake fluid by substitution
Some car owners believe that a simple replacement of the brake fluid by replacement takes place, since the fluids mix and the brake fluid will gradually push out all the water, but this is not the case. Water is heavier than brake fluid, and if it is already present in the reservoir, then there is even more of it in the brake caliper and it can only be displaced by a complete replacement, the bleeder screw is unscrewed and drained. Otherwise, the fluid does not change.
Article rating
Brake fluid is a type of hydraulic fluid that is used in hydraulic brake systems and hydraulic clutch systems on automobiles, motorcycles, light trucks as well as bicycles. The fluid is used to transmit pressure and to increase braking force.
General information about brake fluid
The principle of operation of the brake fluid is its low compressibility. Molecules do not have an internal void, so when compressed, the volume of the liquid does not decrease, and the pressure quickly spreads to the entire volume.
The composition of the brake fluid
Brake fluid comes in many types, but is usually made from a low viscosity solvent, such as alcohol, and a viscous, non-volatile substance, such as glycerin.
Based on polyethylene glycol, brake fluid is produced under the brands DOT 3, DOT 4 and DOT 5.1.
Based on silicone - organosilicon polymer products grade DOT 5.
For vehicles with anti-lock braking systems, DOT 5.1/ABS brake fluids based on silicone and glycols can be used. About brake fluid wiki: link.
Characteristics and properties of brake fluid
In order for the brake system to work 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 surrounding 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, as in this case, moisture evaporates from the fluid in the form of vapor. And steam is dangerous because it is easily compressible and the pressure on the brakes will be less during the next braking, since the compressible steam will take away part of the volume.
The boiling point of brake fluid is directly related to 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 brake brands have minimal hygroscopicity (moisture absorption), for example, DOT 5, and can maintain the necessary characteristics throughout their 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. How the brake fluid will be pumped throughout the system will depend on this characteristic. And it should pump well and at -30 degrees Celsius and at 200 degrees, during braking.
If the liquid freezes completely or in places, then this blocks the operation of the brakes. Too thick fluid will be difficult to pump throughout the system, which will either lead to poor braking or different force on different wheels. Too liquid will cause leaks.
Corrosion protection. The brake fluid itself acts as a corrosion protection inside the brake system. At the same time, 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:
- only liquid with a higher rating number can be added, that is, DOT 4 can be poured into DOT 3, 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.
- Do not mix mineral (eg LHM+) and glycol fluids.
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 runs. These are general recommendations.
If the car is operated in severe conditions, then 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, anti-corrosion additives work worse. You can use the topping up method only when carrying out repairs or in case of a leak, when you just need to get to the service station or garage.
You can identify unsuitable brake fluid:
- Through a complete analysis using special equipment.
- "By eye" - the old liquid is dark in color, while the new one is translucent.
- A device that measures the amount of moisture in a liquid. If less than 3.5 percent, then you can still drive.
It is necessary to fill in the brake fluid in the expansion tank of the brake system. It is usually located above the master brake cylinder and serves to compensate for the brake fluid when it is heated, as well as to prevent air from entering the system.
The fluid level in the tank must be between the "MIN" and "MAX" marks. In modern cars, there is a float with a sensor that will notify the driver that the fluid level in the reservoir has dropped below the minimum mark.
How to change brake fluid
It is best to do this at specialized service stations. Most modern cars have an ABS system, and this leaves its mark on the procedure. Special equipment is needed to bleed the system with new fluid.
If you are told that it is possible to change the brake fluid without bleeding without special equipment, then do not listen to these tips. Yes, on some wheels the pressure from the reservoir can push through the system, but on all it will not work. 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 volume of brake fluid averages from 0.75 to 1.3 liters.
Visually replacing the brake fluid without special equipment is described in the video below:
brake fluid prices
Typically, 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, so keep them 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 the eyes, rinse them thoroughly with clean water and consult a doctor.
The brake pedal usually falls to the floor at the most inopportune moment. When brakes are most needed
By science
Real stories about how they managed to get out of such a difficult situation are almost inaudible among drivers: without being able to stop, it is difficult to survive on a mountain serpentine or in front of an obstacle “rolling” at a speed of two hundred ... And those who are lucky often talk about miracle: absolutely serviceable brakes with unworn friction surfaces (pads, discs, drums) failed. The pedal "suddenly" failed, and after a while "recovered". One could really believe in evil fate, if not for one detail, or rather, liquid. Brake, of course.
In the brakes, it plays no less a role than any other part of the system. Their performance, and hence the lives of people, depends on its condition.
Any liquid, when heated, begins to boil, i.e., to move from one state of aggregation to another. A gas, unlike a liquid, is easily compressible. There is plenty of heat in the brakes: with frequent hard braking, the brake pads heat up to almost a thousand degrees. When the liquid boils in the hydraulic drive of the brakes, its vapors (i.e., the gas phase) are easily compressed, the pedal goes to the floor. This problem has been known since the dawn of motoring and since then, as power and speed have grown, it has been regularly successfully solved. Each time, chemists find a new compound that doesn't freeze at low temperatures and doesn't 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 good for everyone, one problem: they actively absorb water from the air. The boiling point of the liquid gradually decreases, reaching the maximum allowable (150°C). Almost all car manufacturers recommend replacing GTZ every two years or 60 thousand kilometers. Continued use is dangerous.
“Thrifty” car owners justify themselves by saying that they don’t drive fast, and they don’t 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, the matter will not reach the complete freezing of the liquid, but the braking efficiency may deteriorate. And the most unpleasant thing is that the "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 a few vigorous braking it suddenly becomes “sluggish”. There is no need to talk about saving money, even if an accident was avoided.
Brake pipes today are made mostly of steel. With the old liquid, despite the presence of a protective coating, they rust not only from the outside, but also from the inside. And how do you know if corrosion centers will appear soon? Moreover, designers, believing that their recommendations are certainly followed, often use materials that are incompatible in aggressive environments. A typical example is aluminum pistons in cast iron brake cylinders. A little bit of moisture, and the pistons soured, lost their mobility due to corrosion. A bottle of fresh brake fluid costs no more than one cylinder. How many are on the car? Let's add tubes and work. Are you so rich that you can afford not to change the fluid for years?
On practice
We brought a small red suitcase with the TRW logo from Frankfurt from Automechanika-2008. It contains an electronic brake fluid tester (YMB 214). The instruction is in 19 languages, but without Russian. In the near future, the device will also be available in Moscow, and then a Russian page will appear. However, you can do without it. Working with the device comes down mainly to three actions: correctly connect the clamps to the battery, put the “trunk” of the device into a tank with liquid and read the readings on the scale. Let's try to find out how safe the cars around us are.
Fight check
The cavalry charge with horrifying results failed. It can be seen that the object for the attack was chosen unsuccessfully. 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 even give us money for spare parts. We are guided by the color of the brakes. Our conclusion: there are no color-blind people at the carpool.
All tested vehicles were filled with conditioned brake fluid. The temperature of all samples was in the range 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. In the Gazelles, Volga and Fours, which make up the majority of the fleet, GTZ DOT-4 is used. Excellent result!
We go outside, right in front of the editorial office. Year-old "Sable" 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 reservoir cap of the main brake cylinder caused outright 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 fluid level. The result was shocking - 193 ° C for a liquid that has served much more than it should! And this is in St. Petersburg, "famous" for its marsh climate and the corresponding humidity.
The third day of testing was carried out in a garage cooperative. And not in vain. Only here cars with "criminal" brake fluid were found. The worst result (127°C) was recorded in a 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 caliper assembly and regularly added brake fluid, but he could not remember when he did it. 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 claim to be scientific or completely objective. We were able to persuade less than a hundred car owners to check the GTZ. A negative result was found only in isolated cases. More accurate data could be given by service station specialists armed with a similar tester. Our observations confirm only 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 manual should still not be neglected.
TRW YMB 214
The device is designed specifically for the needs of service companies involved in the repair and maintenance of brakes. It allows you to determine the condition of the used brake fluid in the master cylinder reservoir. Food - from the accumulator battery of the car (12 V).
The use of the device allows you to replace the GTZ in time, preventing the development of internal corrosion and the failure of the brakes, both due to boiling of the liquid, and due to malfunction of cylinders and pipelines. In the process of replacing the fluid, other defects can also be identified, the elimination of which is useful for the owner, who receives a guaranteed serviceable car from the repair, and is beneficial for the service, as it provides an additional workload for employees.
Wheelbarrow for pumping
Replacing the brake fluid is not much different from bleeding the brakes. Hoses are put on all bleed fittings, the second ends of which are lowered into transparent containers. All valves open at the same time. We squeeze the old fluid out of the system by sharply pressing and gently releasing the brake pedal. Drain the spilled liquid into another container. It can be useful for loosening tight, rusty nuts.
We put containers under the hoses again, pour fresh liquid into the tank and pump the pedal in the same rhythm until liquid appears in the vessels. We wrap all fittings and pump the brakes in the sequence indicated in the instruction manual. It is better not to use fresh drained liquid for its intended purpose.
Tale with commentary
There was such a bike among Leningrad taxi drivers in the seventies. The taxi driver drove at full speed, in a hurry with a passenger to the airport. I wanted to jump on 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 brake failure was recorded in the protocol, he removed from the pedal not a stiff, but a stiff leg. The next time you pressed the brakes worked fine. The cause of the accident was recognized as not entirely clear factory defect. But most likely it was the old or low-quality brake fluid. The resourceful (and patient) driver got away with it. The taxi company paid for the broken car. Whether a claim was made to GAZ, history is silent.
It is pointless to repeat the "feat of a taxi driver" on your car: the owner himself is responsible for its technical condition. The only exception is a brand new car. For a factory marriage, there is a chance to bring the manufacturer to justice.
Another thing is if you are a hired driver and you have recently been driving a car that has been in an accident. 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 fluid in time.
When fluid does not leak in the hydraulic brake drive, it would seem that no attention should be paid to it. However, the efficiency of braking and the stability of the system depends on its condition. If, for example, bad 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%).
Outdated liquids, such as "BSK", are made from a mixture of castor oil and butyl alcohol in a 1: 1 ratio. The basis of modern, most common, including domestic ones ("Neva", "Tom" and RosDOT, aka "Rosa"), are polyglycols and their ethers 1 . Much less frequently used silicones 2 .
In the complex of additives, some of them prevent the oxidation of fuel oil by atmospheric oxygen and during strong heating, while others protect the metal parts of hydraulic systems from corrosion.
Basic properties of any brake fluid depend on the combination of its components.
- Boiling temperature. The higher it is, the less likely it is that a vapor lock will form in the system. When the car brakes, the working cylinders and the fluid in them heat up. If the temperature exceeds the allowable temperature, the TJ will boil and vapor bubbles will form. The incompressible fluid will become "soft", the pedal will "fail", and the car will not stop in time.
- The faster the car was driving, the more heat generated during braking. And the more intense the deceleration, the less time will be left for cooling the wheel cylinders and supply pipes. This is typical for frequent long-term braking, for example, in mountainous areas and even on a flat highway loaded with vehicles, with a sharp "sporty" driving style.
The sudden boiling of TJ is insidious in that the driver cannot predict this moment.
- Viscosity characterizes the ability of the liquid to pump through the system. The temperature of the environment and the TJ 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 main cylinder and its tank), and even up to 200°C with intensive deceleration of the car ( in working cylinders). Under these conditions, the change in the viscosity of the liquid must correspond to the flow sections and gaps in the parts and assemblies of the hydraulic system, specified by the vehicle developers.
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 brake response time. And too liquid - increases the likelihood of leaks.
- Impact on rubber parts. Seals should not swell in the TJ, 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 car may slow down. With sagging seals, the system will be leaky due to leaks, and deceleration will be ineffective (when you press the pedal, the fluid flows inside the master cylinder without 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 liquid 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 out less, brake fluid must lubricate their working surfaces. Scratches on the cylinder mirror provoke TJ leaks.
- Stability- resistance to high temperatures and oxidation by atmospheric oxygen, which occurs faster in a heated liquid. TJ oxidation products corrode metals.
- Hygroscopicity- the tendency of polyglycol-based brake fluids to absorb water from the atmosphere. In operation - mainly through the compensation hole in the tank lid.
The more water is dissolved in TF, the earlier it boils, thickens more 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 that regulates the quality indicators of brake fluids. Domestic manufacturers work according to their own specifications, focusing on the standards adopted in the USA and Western Europe (standards 3 J1703, ISO (DIN) 4925 and FM VSS N116). Liquids are classified by boiling point and viscosity, their other properties are similar.
Which TJ should be used in a car is decided by its manufacturer. As a rule, DOT 3 class fluids are designed for relatively slow-moving cars with all drum or disc brakes in front. TJ with improved performance characteristics that meet the requirements of DOT 4 are designed for modern cars with improved dynamic qualities. Such machines allow frequent hard accelerations and intense decelerations, and they have predominantly disc brakes on all wheels. DOT 5 class fluids are rarely used, mainly on road sports cars. The thermal loads on the 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 TF. At the same time, their boiling point decreases. FM VSS normalizes it only for "dry" liquids that have not yet collected moisture, and moistened liquids containing 3.5% water - i.e. limits only limit values. The intensity of the absorption process is not regulated. TJ can be saturated with moisture at first actively, and then more slowly. Or vice versa. But even if the boiling point values of "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 testing, TF manufacturers usually plot boiling point curves. Each fluid has its own.
TJ must be replaced periodically, without waiting for its condition to approach a dangerous limit. The service life of the fluid is assigned by the car factory, having checked its characteristics in relation to the features of the hydraulic systems of its machines.
Checking the condition of the liquid. It is possible to objectively determine the main parameters of TJ only in the laboratory. In operation - only indirectly and not all.
Independently, the liquid is 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 liquid does not circulate in the system, its properties may be different in the tank (test point) and in the wheel cylinders. In the tank, it comes into contact with the atmosphere, gaining moisture, but not in the brake mechanisms. But there the liquid often and strongly heats up, and its stability deteriorates.
However, even such approximate checks should not be neglected, there are no other operational methods of control.
Compatibility. TJ with different bases are incompatible with each other, they delaminate, 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 the TJ on the packaging. Russian RosDOT, Neva, Tom, as well as other domestic and imported polyglycol 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, the FM VSS 116 standard requires that "silicone" liquids be colored deep red. The rest of modern TJs are usually yellow (shades from light yellow to light brown).
For additional verification, you can mix the 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 remains practically unchanged. Therefore, within the time limits established by the car factory, the fluid in the hydraulic system must be completely replaced. The sequence and features of this operation, for example, pumping with the engine running, depend on the design of the system (type of amplifier, anti-lock devices, etc.) and are known to service station specialists. This information is often found in the vehicle owner's 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 fill the tank with fresh liquid and pump it in by pressing the pedal. The valves are sequentially closed when TJ appears from them. Then air is removed from each circuit (branch) of the hydraulic drive.
- The disadvantage of this technique is the need for a final (control) pumping of the system. In addition, a drain hose must be put on each valve, lowering its other end into a suitable container5 - the leaking TJ can damage tires and paint on suspension parts, brakes, wheels. On the other hand, the new liquid is guaranteed not to mix with the old one, and part of the fresh TJ that came out during pumping, allowing it to settle to remove air and filtering, can be reused.
- The replaceable TJ is replaced with fresh one, constantly topping it up in the master cylinder reservoir and preventing the system from draining. To do this, each circuit is pumped in turn until fresh fluid appears from the valve.
- In this case, air does not enter the hydraulic actuator, but it is possible that part 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
It is necessary 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.
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, it is necessary to wash or lubricate the cuffs, and even metal parts, only with fresh, clean brake fluid.
- Brake fluids "Neva", "Tom" and RosDOT are flammable, and "BSK" is flammable. Smoking while working with them is prohibited.
- TJ is poisonous - even 100 cm3 of it that 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 case of ingestion of TJ, for example, when trying to pump out part of it from the master cylinder reservoir, you must immediately induce vomiting (see our certificate). If liquid gets into eyes, rinse them with water. 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 cups of soapy water;
- a glass of warm water in which a teaspoon of dry mustard is diluted.
- You need to choose the TJ recommended by the car factory.
- Liquid packaging must be airtight. With light pressure from the sides, it springs.
- The membrane under the lid is preferably made of foil - this does not let water through and indicates the solidity of the manufacturer.
The editors are grateful to Ph.D. E. M. Vizhankova and senior researcher G. I. 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, and are efficient in the temperature range from minus 100 to 350°C.
3 SAE - Society of Automotive Engineers (USA), ISO (DIN) - International Organization for Standardization, FM VSS - Safety Measures Act (USA).
4 Silicone-free DOT 5.1 fluids are sometimes referred to as DOT 5.1 NSBBF, and silicone DOT 5 as DOT 5 SBBF. The abbreviation NSBBF stands for "non silicon based brake fluids" and SBBF stands for "silicon based brake fluids".
5 The same must be done when removing air from the system or its circuit. In addition to damage to parts, splashes of pressurized fluid from the valve can enter the eyes.
Based on site materials www.zr.ru
