Every motorist has come across a situation where it is necessary to change or add brake fluid to the system. If you regularly technical inspection service, then there will be no problems in the future. It will be enough just to change the specialized fluid, following the manufacturer's recommendations. It should be noted that brake fluid is different type, this should not be forgotten. If you fill wrong option, then over time there will be trouble.
But there are times when brake damage occurs on the road, far from the location of your garage or service. In this scenario, many drivers simply add fluid to get required level. Due to this, you can get to the place and produce complete replacement systems. It will be good if the driver is prudent and carries with him enough special fluids and the like. Otherwise, you will have to fill in the first one that comes across, which is sold in the nearest store. And this is quite bad, since you do not know the quality of products and features. Before filling, you should consider whether it is possible to mix the purchased products with those in the brake system. You will try to consecrate a similar question in the article.
Currently, you can find several varieties of brake fluids:
1) DOT - 3. This type of liquid has an oily base and a light brown tint. The boiling point is within 200 degrees Celsius. Recommended for vehicles that are equipped with a drum brake system, such as trucks and similar vehicles. Everyone knows that during braking, the drum system heats up much less than the disc system;
2) DOT-4. This variety has a transparent color, in which cases a light brown tint. As for the boiling point, it varies within 230 degrees Celsius. It is used in all motorcycles and some cars;
3) DOT-5. Brake fluid has a reddish tint and a boiling point of around 180 degrees Celsius. Recommended for use in sports vehicles And powerful motorcycles. After all, it requires not only good dynamic properties but also an excellent braking system;
4) DOT-5, 1. Has an oil base like all other brake fluids. A small feature is the boiling point, it varies within 260 degrees Celsius. As for the color itself, the brake fluid has a yellowish tint. In fact, this is a slightly improved version when compared with the previous generation.
How often to change fluid?
Brake fluid is recommended to be changed at least once every two years, regardless of the car model, as it works in heavy operating conditions– heats up to high temperature during frequent braking. The “brake” is also hygroscopic, and over time, moisture accumulates in its composition, from which the boiling point of the TF decreases. If too much moisture accumulates, the fluid will boil when braking, the car's brakes will fail.
You also need to change the brake fluid:
1) when buying a used car - it is not known when the previous owner serviced the vehicle for the last time;
2) when the liquid becomes cloudy or a precipitate appears in it.
The industry has developed special testers that check the hygroscopicity of TJ, an example is the Novitec device. On his front panel There are four indicators:
1) Gut;
2) 1%;
3) 2%;
4) 3%.
When, when checking the brake fluid on the tester, lights up green indicator Gut, this means that the brake fluid meets the requirement of hygroscopicity and does not contain water in its composition. 1% - the condition of the "brake" is satisfactory, 2 and 3% - the fluid must be changed, it is not suitable for further use.
What is brake fluid made of??
Combines all brake fluids, with the exception of DOT-5, their base component is polyethylene glycol. The basis for the creation of DOT-5 is silicone. You should remember that the composition of DOT-5.1 is fundamentally different from DOT-5, which is consonant with it. If there is an emergency, the combination of DOT-3, DOT-4 and DOT-5.1 is permissible, since they have a common base. Even better if they were made by the same manufacturer. At the same time, we must not forget that adding another DOT-3 liquid to the DOT-4 liquid, you thereby lower the boiling point of the first one. If you mix liquids made on different components, that is, silicone and polyethylene glycol, as a result of the reaction between them, a composition is formed that simply is not a brake fluid, which is extremely dangerous for further movement.
Which liquids to mix and which should not:
Based on the foregoing, it is worth remembering that in no case should you:
1) allow mixing a composition such as DOT-5 with any of the above, they are completely incompatible;
2) connect in the brake system of a car with ABS, fluids, one of which is designed for ABS, and the second is not;
3) add a liquid such as DOT-3 to DOT-5.1: the resulting mixture will boil at a lower temperature;
4) the mixing of DOT-4 and DOT-3 threatens the same - a decrease in the boiling point of the resulting mixture.
In case of emergency, it is allowed to add:
1) DOT-4 when DOT-3 is in the system;
2) DOT-5.1 to the main DOT-3;
3) DOT-5.1, when the working composition is DOT-4. The resulting mixture boils at a higher temperature than the initial one, which, in principle, is allowed.
It is not recommended to interfere with liquids released under different trademarks. Each manufacturer does everything to give their product high quality by adding a variety of additives. It is difficult to predict how these liquids will behave during interaction. Whatever combination of fluids you use, the first thing to do after suddenly topping up brake fluid on the road, reaching your destination, is to completely change the entire mixture in the brake system. If you plan to replace DOT-4 with a newer DOT-5, you will need to flush the brake system in order to eliminate residual fluid.
Flushing the system must be done in the following cases:
1) if one type of “brake” changes to another;
2) in case of turbidity of the brake fluid or precipitation in it;
3) if available in old fluid a large number moisture.
The principle of washing is as follows:
1) using a syringe, the liquid is pumped out of the tank;
2) the brakes are bled until fresh brake fluid flows out of the fittings;
3) the operation is repeated several times, then the system is filled with a new "brake", the brakes are finally pumped.
Remember, it never hurts to carry a supply of the exact brake fluid that is filled in your car with you, in order to avoid situations where you need to risk and mix Various types liquids. After all, it is not always possible to know what this will lead to. It may take a lot of time and Money for recovery.
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 possible exploitation liquids. 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: FMVSS No. 116, ISO 4925, SAE J1703 etc. In real conditions working temperature 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 out into the tank of the main 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 will not notice this, but emergency braking on the track… 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 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, and 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 by by and large easily. 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 circumstances, more frequent replacement 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 big, but for the sink high pressure not calculated.
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.
There is no production standard in Russia 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.
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 shorten the life of the engine. low quality brake fluid can cause an accident.
General information
Brake fluid (TF) consists of a base (its share is 93-98%) and various additives (the remaining 7-2%).
Outdated fluids, 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, when strong heat, while others protect 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. Temperature 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 summer in engine compartment(in the main cylinder and its tank), and even up to 200°C with intensive deceleration of the machine (in the 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 when 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 on their own specifications, focusing on the norms adopted in the USA and Western European countries (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 low-speed machines with all drum brakes or disc front. TG with improved operational characteristics, which meet the requirements of DOT 4, are designed for modern cars with increased 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 on boiling points, and "BSK" - also on 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 standardizes 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 points of "dry" liquids different classes make them 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 check the liquid visually - according to appearance. It should be transparent, homogeneous, without sediment. In addition, in car services (mainly large, well-equipped, servicing foreign cars) special indicators evaluate its boiling point. 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, and in brake mechanisms- No. 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 specialists service stations. This information is often found in the vehicle owner's manual.
On domestic cars the fluid is replaced by one of the following two methods.
- 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. But new fluid it is guaranteed not to mix with the old one, and part of the fresh TJ that came out during pumping, after letting it settle to remove air and filtering, can be used again.
- 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 withstands high temperatures well, but such rubber is destroyed 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.
_____________________________________
1 Polyglycols and their esters - group chemical compounds based on polyhydric alcohols. They have heat boiling point and good low temperature properties.
2 Silicon-organic polymer products. Their viscosity depends little on temperature, they are inert to various materials, are efficient in the temperature range from minus 100 to 350°C.
3 SAE - Society 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
The liquid is not compressible. This law is known to us high school, and it is on it that the operation of the brake system of a modern car is based. What happens if there are exceptions to the law? You say it doesn't happen. Sometimes the owner of the car creates them with his own hands, violating the frequency of replacing the brake fluid. Consider typical faults, which may arise due to its untimely replacement and non-compliance with the rules for performing this operation.
Why change brake fluid? She works in enclosed space, and its properties cannot be changed.
Brake fluid works in a space that can be called closed rather conditionally. The system has compensation holes that let air into it when you press the pedal, and release it when it is reversed. As a result, the brake fluid, which contains, among other substances, various alcohols, absorbs moisture from the surrounding air (the brake fluid is hygroscopic). In addition, irreversible chemical reactions take place in it, and the additives that make up the brake fluid lose their properties over time. Therefore, its composition changes over time, and quite significantly.
Modern brake fluids can be mixed in any proportion.
Indeed, brake fluids can be mixed, but not all and not with all! Only those of them that meet the same standards are mixed. But it should be noted that liquids from different manufacturers, as a rule, have different additive formulations, and sometimes they are made on a different basis. In addition, you cannot always be sure of the brand of fluid poured into the brake system. Therefore, it is still better not to mix brake fluids, as if they are incompatible, the brakes may fail.
IN modern cars any brake fluid that meets DOT-4 standards can be used.
This is a misconception. A number of car manufacturers allow the use in brake systems only specially formulated liquids. Some of them are based on mineral basis, so it is strictly forbidden to mix them with glycol fluids. The use of glycol fluids in the brake systems of vehicles designed for mineral water is also unacceptable. Leading manufacturers of brake fluids usually warn consumers directly about this.
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GENERAL INFORMATION
When you press the brake pedal, the force through hydraulic drive is transmitted to the wheel (working) brake mechanisms that stop the car due to friction forces. If the heat released at the same time heats the brake fluid beyond its permissible limit, it will boil and vapor locks will occur. The mixture of liquid and vapor will become compressible, the brake pedal may "fall through" and brake failure will occur. To eliminate this phenomenon, special brake fluids are used in hydraulic drives. They are usually classified by boiling point and viscosity in accordance with DOT standards - Department of Transportation (Department of Transportation, USA). Distinguish between the boiling point of a "dry" liquid that does not contain water and "moistened" - with a water content of 3.5%. Viscosity is determined at two temperatures: +100°C and -40°C. These indicators, corresponding to the American federal standard for vehicle safety FMVSS No. 116, are presented in the table. Similar requirements are contained in other international and national standards - ISO 4925, SAE J 1703, etc. In Russia, there is no single standard regulating the quality indicators of brake fluids, and domestic producers operate under various specifications.
brake fluids various classes mainly apply:
- DOT 3 - for relatively slow vehicles with drum brakes or disc front brakes;
- DOT 4 - on modern high-speed vehicles with predominantly disc brakes on all wheels;
- DOT 5.1 - on road sports cars, where the thermal load on the brakes is much higher.
Note. DOT 5 class fluids are practically not used in conventional vehicles.
PERFORMANCE REQUIREMENTS
In addition to the main ones - in terms of boiling point and viscosity, brake fluids must meet other requirements. No negative impact on rubber parts. Rubber cuffs are installed between the cylinders and pistons of the hydraulic drive of the brakes. The tightness of these joints increases if, under the influence of brake fluid, the rubber expands in volume (for imported materials, an expansion of no more than 10% is allowed). During operation, the seals should not swell excessively, shrink, lose elasticity and strength.
Protection of metals from corrosion. Brake hydraulic drive units are made of various metals interconnected, which creates conditions for the development of electrochemical corrosion. To prevent it, corrosion inhibitors are added to brake fluids to protect parts made of steel, cast iron, aluminum, brass and copper.
Lubrication of friction pairs. The lubricating properties of the brake fluid determine the wear of the working surfaces of brake cylinders, pistons and lip seals.
Stability at high and low temperatures. Brake fluids in the temperature range from minus 40 to plus 100°C must retain their original properties (within certain limits), resist oxidation, delamination, and the formation of sediments and deposits.
TYPES OF BRAKE FLUIDS AND THEIR COMPATIBILITY
Brake fluids consist of a base (its share is 93-98%) and various additives, additives, sometimes dyes (the remaining 7-2%). According to their composition, they are divided into mineral, glycol and silicone.
Mineral, which are various mixtures in a 1: 1 ratio of castor oil and alcohol, such as butyl (red-orange liquid "BSK"). Such liquids have good lubricating and protective properties, are non-hygroscopic, and are not aggressive to paintwork. But they do not meet international standards in terms of basic indicators - they have a low boiling point (they cannot be used on machines with disc brakes) and become too viscous already at minus 20°C.
Mineral fluids must not be mixed with glycol fluids, otherwise the rubber cuffs of the hydraulic drive units may swell and the formation of castor oil clots.
Glycols based on polyglycols and their ethers are groups of chemical compounds based on polyhydric alcohols. They have a high boiling point, good viscosity and satisfactory lubricity. The main disadvantage of glycol fluids is hygroscopicity - the tendency to absorb water from the atmosphere. In operation, this mainly occurs through the compensation hole in the reservoir cap of the master cylinder. The more water dissolved in the brake fluid, the lower its boiling point, the greater the viscosity at low temperatures, the worse the lubricity of parts and the stronger the corrosion of metals. Domestic and imported glycol fluids of DOT 3, DOT 4 and DOT 5.1 classes are interchangeable, but it is undesirable to mix them, since the basic properties may deteriorate in this case.
On vehicles more than twenty years old, the seal rubber may not be compatible with glycol fluids - only mineral brake fluids must be used for them (or all seals will have to be changed).
Silicone, made on the basis of organosilicon polymer products. Their viscosity depends little on temperature, they are inert to various materials, workable in the temperature range from –100 to +350°C and do not adsorb moisture. Their use is particularly limited by insufficient lubricating properties. Silicone-based fluids are incompatible with others.
DOT 5 silicone fluids should be distinguished from DOT 5.1 polyglycol fluids as similar names can lead to confusion. For this, the packaging additionally indicates:
DOT 5 - SBBF ("silicon based brake fluids" - brake fluid based on silicone).
DOT 5.1 - NSBBF ("non silicon based brake fluids" - brake fluid not based on silicone).
CHECK AND REPLACE
On modern cars, due to a number of advantages, glycol brake fluids are mainly used. Unfortunately, in a year they can “absorb” up to 2-3% of moisture and they need to be replaced periodically, without waiting for the condition to approach a dangerous limit (see fig.). The replacement interval is indicated in the car's operating instructions and usually ranges from 1 to 3 years. An objective assessment of the properties of the brake fluid is possible only as a result of laboratory tests. In practice, the state of the brake fluid is assessed visually - in appearance. It should be transparent, homogeneous, without sediment. There are devices for determining the state of the brake fluid by boiling point or degree of moisture. But since the liquid does not circulate in the system, its condition in the tank (test point) may be different than 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 is often very hot, as a result of which its original properties deteriorate.
Adding fresh brake fluid when bleeding the system after repair work, practically does not improve the situation, since a significant part of its volume remains unchanged.
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 brake system (type of booster, availability of anti-lock devices, etc.). This information is often found in the vehicle owner's manual.
On domestic cars, the brake fluid is replaced in one of the following two ways.
1. Completely drain the old fluid by opening all valves (fittings) for releasing air from the hydraulic brake drive. Then fill the tank with fresh fluid and pump it into the system by pressing the brake pedal. The valves are sequentially closed when liquid appears from them. Then air is removed from each circuit (branch) of the hydraulic drive (“pumping” the brakes). With this method, the new fluid does not mix with the old. Part of the fresh liquid released during pumping can be reused (letting it settle and filtering).
Note. Before starting the operation, a drain hose must be put on each valve, lowering its other end into a suitable container - escaping brake fluid can damage tires and paint coatings on suspension parts, brakes, wheels.
2. Each circuit is pumped in turn, constantly adding fresh liquid to the master cylinder reservoir and thus displacing the old one, preventing the system from draining. This is continued until fresh fluid flows from the valve. With this option, air cannot get into the hydraulic actuator and control "pumping" is not required. But it is possible that some of the old fluid will remain in the system. In addition, more fresh fluid will be required than when pumping in the previous way. This is due to the fact that most of it, removed from the hydraulic drive, mixes with the old one and becomes unsuitable for further use.
SECURITY MEASURES
Store any brake fluid only in a hermetically sealed container so that it does not come into contact with air, does not oxidize, does not pick up moisture and does not evaporate.
Brake fluids are generally flammable or flammable. Smoking while working with them is prohibited. Brake fluids are poisonous - even 100 cm3 of it that gets inside the body (some fluids smell like alcohol and can be mistaken for an alcoholic drink) can lead to the death of a person. In case of ingestion of liquid, for example, when trying to pump out part of it from the reservoir of the master cylinder, you must immediately flush the stomach. If the liquid gets into the eyes, rinse them with plenty of water. And in any case, you should consult a doctor.
