T brake fluid
Continuing the theme of the brake system started earlier, of course, one cannot ignore the brake fluid (TF). I would like to answer the main questions related to this topic:
- Appointment of TJ.
- Main properties of TG
- How to choose a TJ
- TJ replacement
So, let's figure out what is being said, point by point.
Appointment of TJ.
To begin with, it should be understood that TJ is an integral part of the hydraulic brake system. It is designed to transfer pressure from the master brake cylinder to the wheel cylinders. It happens like this:
When you step on the brake pedal, you are actually pressing on the master cylinder piston, which pushes brake fluid through a series of tubes and hoses into the brake cylinder at each wheel. In disc brakes, brake fluid from the master cylinder pushes the piston under pressure. The piston, in turn, compresses the brake pads on the brake disc, which is attached to the wheel. In drum brakes, fluid is forced into the brake cylinder, which pushes the brake pads so that the friction linings press against the drum, which is attached to the wheel. In both cases, as a result, the wheel slows down or stops.
The disadvantage of the hydraulic drive is that in case of depressurization, the brake fluid completely or partially flows out of the system, which can lead to brake failure. To prevent such a situation in modern machines, dual-circuit hydraulic brake actuators are used. The essence of their design is that they consist of two independent circuits - separately for each pair of wheels. Note that these contours do not necessarily link the wheels of the same axle: for example, the left front wheel can be connected to the right rear wheel, and the right front wheel to the left rear wheel. If for some reason one circuit fails (for example, brake fluid has leaked out, a brake cylinder has jammed, etc.), then the second circuit is activated. Of course, the effectiveness of such braking drops noticeably, but still it allows you to stop the car and avoid serious troubles.
The main properties of TJ.
TJ conducts pressure in the brake system in the same way that wires conduct electricity in the mains. Accordingly, just as the wires are not made from the first material that comes across, so the TJ must have certain properties for better pressure conductivity in the system. Although the task is narrow, it is very responsible, because the braking system has no right to fail under any circumstances.
Being a special oil, it must not change its properties (remain liquid) at low and very high temperatures and retain these properties for a long time. What are these properties?
Boiling temperature. Experience shows that the operating temperature of the brake fluid at the hottest points in the system is approximately the following: 60 ° C when driving on the highway, 100 ° C in city mode and 120 ° C when driving on a mountain road. But this is an average, and in stressful conditions (trips with a trailer, during sports driving) it often reaches 150 ° C and even more, and when the car stops, it briefly jumps up to 200 ° C, because, for example, the brake pad heats up during several emergency braking up to 600 ° C. Therefore, the liquid may boil in an unfavorable situation. When boiling in the TJ, microscopic air bubbles form and, when you press the brake pedal, part of the liquid overflows into the expansion tank of the main brake cylinder (GTZ), and the liquid remaining in the system does not create the necessary pressure. This is due to the fact that the transmitted pressure is primarily used to compress the bubbles. For the driver, this is expressed in the "failure" of the brake pedal, i.e. the effectiveness of such braking is significantly reduced. Of course, modern liquid fuels are designed for such loads and their boiling point is much higher than the critical one (that is, 150 ° C), but this should not be deceived. Do not forget about such a property of TJ as hygroscopicity - the ability to absorb moisture from the air, and rubber cuffs serve as a poor barrier to this process. Accordingly, with an increase in the proportion of moisture in the TF, its boiling point decreases. During the year of operation, the TJ absorbs approximately 2-3% of water. Therefore, in the TJ data, two values \u200b\u200bof the boiling point are always indicated: “dry” - without moisture and “moistened” - with a content of 3.5% water. The boiling point of the latter indirectly characterizes the temperature at which the liquid will boil after 1.5-2 years of its operation in the hydraulic drive of the car brakes. If it is small, then such fluid should not be used in a system with disc brakes.
Frost resistance. What happens if the TJ does not have sufficient frost resistance, i.e. does it change its viscosity properties with decreasing temperature or does it freeze at all? It is obvious that the pressure-transmitting fluid must maintain acceptable fluidity even in extreme cold. If the viscosity increases, then the time interval for the operation of the brakes increases noticeably, which is naturally unacceptable. It is accepted that the viscosity of the TJ should not exceed 1800 mm 2 /s at -40°C for the normal version and 1500 mm 2 /s at -55°C for the special northern version. When choosing a product for use in harsh winter conditions, this should be taken into account. After all, if ice crystals form in the TJ during frost, then a few presses on the brake pedal are enough to damage the sealing cuffs and, of course, the brakes will fail.
Anti-corrosion and lubricating properties. For moving parts of the brake system, due to the absence of any other anti-friction products, TJ is a natural lubricant. Accordingly, the TJ must contain special additives and additives that ensure the longest and most reliable operation of the rubbing pairs of the brake system, protecting them from corrosion, excessive wear and scoring.
Seal compatibility. Or 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. In this case, the shape and properties of the rubber change, there are gaps in the seals and rubber hoses, and their gusts are possible. All this leads to brake failure.
Also, the additives contained in the TJ must resist its oxidation, delamination, the formation of sediments and deposits.
How to choose TJ?
To determine the quality of the TJ, what is said “by eye” and how it will interact with the details of the brake system, of course, is not acceptable. Therefore, when choosing TJ, first of all, remember that this is one of those products that you should not buy in markets and other dubious points. If low-quality engine oil leads to a decrease in engine life, then low quality TJ threatens you with an accident! Poor-quality TJ can cause severe swelling of rubber cuffs, corrosion of hydraulic drive units; as a result, the pistons wedged in the working cylinders, the pads do not move away from the discs and gradually heat up. After a couple of hours of driving, such brake fluid in overheated calipers boils, forming steam. As a result, pressing the brake pedal is useless: the air is easily compressed, the pedal rests on the floor, and the car moves almost without slowing down. It is better to give preference to well-known manufacturers (their products are protected by special signs, and it is difficult to fake them), by purchasing liquid from official representatives.
The main criterion when choosing a TJ should be compliance with the requirements of the DOT-Department of Transportation (Department of Transportation, USA), the recommended vehicle. In accordance with these standards, TJ is usually classified by boiling point and viscosity into the following classes:
DOT 3 - applicable for relatively low-speed (in unloaded brake systems) vehicles with drum or disc front brakes;
DOT 4 is an advanced performance fluid used in modern high-speed vehicles with disc and ventilated disc brakes.
DOT 5 and DOT5.1- are used in heavily loaded braking systems (for example, on sports cars), where the thermal loads on the brakes are much higher and are of little interest to the vast majority of motorists.
The desire of chemical engineers to combine the advantages of various fluids “in one bottle” led to the creation of brake fluid BG DOT 4 BRAKE FLUID No. 840 High Performance High Temperature Anti-Lock Braking System Disc and Drum Brake Formula is a premium fluid that exceeds conventional DOT 4 specification tolerances. BG DOT 4 Brake Fluid is an excellent product that maximizes brake component life. BG DOT 4 brake fluid inhibitor system provides excellent protection against rust and oxidation of the entire brake system.
TEST TYPICAL TEST RESULTS
| test data | RequirementsFMVSS No. 116* | RequirementsSAE J1703** | BGDOT 4 |
| Boiling point of "dry" liquid, min | 230°C | 230°C | 266°C |
| Boiling point of the "humidified" liquid, min | 155°C | 155°C | 173°C |
| Viscosity (mm²/cm at minus 40°C) | 1800 | 1800 | 1014 |
| Viscosity (mm²/cm at plus 100°C) | >1,5 | >1,5 | 2,0 |
| pH value | 7-11,5 | 7-11,5 | 8,0 |
| Fluid stability at high temperatures, max | 3°C | 5°C | -1°C |
| Chemical stability (interaction with other substances), max | 3°C | 5°C | -1°C |
| Corrosion aggressiveness, mg/cm², max | |||
| tinned iron | 0,2 | 0,2 | 0,0 |
| steel | 0,2 | 0,2 | 0,0 |
| aluminum | 0,1 | 0,1 | 0,0 |
| cast iron | 0,2 | 0,2 | 0,01 |
| brass | 0,4 | 0,4 | 0,04 |
| copper | 0,4 | 0,4 | 0,02 |
| Oxidation stability (weight change mg/cm², max) | |||
| aluminum plate test | 0,05 | 0,05 | 0,00 |
| steel plate test | 0,3 | 0,3 | 0,02 |
| Water interaction: Precipitation at 60°C, % of maximum volume | 0,15 | 0,15 | Not formed |
| Impact on various types of rubber (NR, SBR, EPDM types) at 70°C | |||
| product diameter change, mm | 0,15-1,4 | 0,15-1,4 | 0,33 |
| increasing the hardness of rubber | Not happening | Not happening | Not happening |
| rubber softening, IRHD, max | 10 | 20 | 3 |
* FMVSS norms (Federal Motor Vehicle Safety Standard) - US Federal Motor Vehicle Safety Standard No. 116 (DOT 4)
** SAE (Society of Automotive Engineers, Inc.)
Brake fluid BG DOT 4 provides additional safety due to its moisture-resistant and lubricating characteristics, as well as the ability to maintain its properties at critical temperatures. It meets Federal Motor Vehicle Safety Standards (FMVSS) No. 116 (DOT 4) and exceeds Society of Automotive Engineers (SAE) J1704 requirements. Suitable for use in conventional and anti-lock braking (ABS) systems that require DOT 4 brake fluid.
Would you like to add your own? This TJ is not cheap, but sorry, you have to pay for the quality. If you want a quality product, then you will not be chasing cheapness. And among the really good TJs, it is quite competitive in price. But what really sets it apart from other DOT4s is its properties. It surpasses similar liquids in many respects and, accordingly, will serve you faithfully for much longer.
For comparison, here you can see the test results of other DOT4 of the most famous brands:
The composition of the TJ is also important. According to it, all TJ can be divided into mineral, glycol and silicone.
Mineral. They have good lubricating properties, they are not hygroscopic, but they do not meet international standards, because. have a very low boiling point (it is not permissible to use them on machines with disc brakes) and already at minus 20 ° C they become viscous.
Glycolic. Most modern products are based on glycol blends. The main disadvantage of glycol fluids is their hygroscopicity. The more water the TF absorbs, the lower its boiling point becomes, the higher the viscosity at low temperatures, the worse the lubricity of parts and the stronger the corrosion of metals. Therefore, it is extremely important to replace such fluids on time.
Silicone. Unlike glycol TF, silicone has water-repellent properties. The viscosity of such a liquid is practically independent of temperature (workable from -100 to +350 ° C). But at the same time, it is not without a number of significant shortcomings that prevent its wide distribution. First, it is a high price. Secondly, it is prohibited for use in vehicles equipped with ABS. And thirdly, this brake fluid is not able to dissolve moisture in itself, which as a result accumulates in calipers and working brake cylinders.
Mixing liquids of different composition is not permissible! When mixing mineral fluids with glycol fluids, the rubber cuffs of the hydraulic drive may swell and the formation of castor oil clots. Silicone-based fluids are not compatible with all others! In this case, attention should be paid to silicone fluids of class DOT 5 and similar in name to DOT5.1 (polyglycol). Although the names are similar, they are different in composition of TJ, and they are not compatible with each other!
Mixing glycol liquids is certainly possible, but not desirable. When they are mixed, the additives contained in them may react. As a result, these additives will be destroyed (TL will lose its anti-corrosion properties at least) or a precipitate may form, which will accumulate not only in the brake reservoir, but throughout the entire system. In any case, keep in mind that by making a "cocktail" of DOT 3 and DOT 4 liquids, you will get a mixture that meets the requirements of DOT 3.
And also take into account that on cars manufactured more than 20 years ago, the rubber of the cuffs may simply not be compatible with glycol fluids - only mineral ones can be used for them.
TJ replacement.
TJ is one of the most important fluids in a car, because an indisputable condition for the safety of driving a car is the efficiency, reliability and reliability of the brakes! Often not only safety, but also the life of the driver depends on this. It is for this reason that the TJ requires regular and timely replacement.
According to the regulations, the TJ is subject to replacement every 2-3 years or 36-60 thousand km. But on some cars, it must be replaced in a shorter time; so, for example, for Maserati, the TJ must be replaced after 10 thousand kilometers, and for Ferrari - after 5 thousand kilometers.
On modern cars, due to a number of advantages, glycolic TFs are used for the most part, and, as we found out earlier, they have high hygroscopicity. For a year of operation, such liquids are able to absorb up to 2-3% moisture. In addition, over time, the additives contained in the TF (such as corrosion inhibitors for example) are developed and may precipitate. Using such a fluid can lead to costly repairs. For this reason, TJ must be monitored! Do not be lazy to check the condition of the TF once a month, especially since most cars have a transparent expansion tank (this was done specifically so that you can monitor the level of TF without opening the lid). In appearance, it should be transparent, homogeneous and without sediment. If the liquid suddenly becomes cloudy or a precipitate appears in it, then it should be replaced as soon as possible, regardless of when you changed it. Further operation of the car with such a liquid can lead to a sudden failure of the brakes! If the expansion tank turns green, then the corrosion inhibitors in the liquid are already at zero and copper begins to immigrate from the brake lines.
In addition to visual control, the condition of the TJ in your car can be determined using test strips BG PF9100. With their help, you can determine the degree of its oxidation, and its suitability for use. The assessment is carried out by measuring the content of copper ions in the liquid. If the liquid is saturated with copper ions, the strip will turn purple.
It is also recommended to replace the fluid in the brake system when buying a used car, since you do not know for certain how often the previous owner changed the fluid and whether it changed at all. In addition, later you will not have to guess what liquid to add if necessary.
Often, instead of the prescribed complete replacement of the TJ, drivers simply add new fluid to the existing fluid. At the same time, a significant part of the liquid volume does not change at all, and the new liquid mixes with the old one and loses its operational properties. Therefore, the fluid in the hydraulic system must be replaced completely! It is best to carry out this procedure at a service station, entrusting the matter to professional mechanics. Indeed, despite the fact that the replacement process itself is quite simple - drained the old one, filled in the new one - air can remain in the system with unskilled intervention, which is fraught with brake failure. To remove air, the brake system must be "bled". This is a rather troublesome business and requires an assistant, as well as certain skills. So we do not recommend experimenting. At a good service station, the brake fluid is replaced by the displacement method on special equipment that supplies fluid under pressure. As a result, bleeding the brakes is not required.
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. For the same reason, always keep the expansion tank closed, except to fill it up. Before pouring liquid, clean any dirt around the cap on the reservoir. Never clean cylinders or other components with gasoline or kerosene. Avoid getting TJ on the car paintwork and brake pads.
NEVER mix TJ with anything! Any other type of oil or fluid will react with the TJ and may destroy the rubber seals in the brake system, causing brake failure.
Brake fluids are generally flammable or flammable. Smoking while working with them is prohibited.
Brake fluids are a deadly poison! - even 100 cm3 of it that got 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 liquid, for example, when trying to pump out part of it from the reservoir of the master cylinder, you should 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.
Why should the choice of brake fluid be taken as seriously as possible? The fact is that the smooth operation of the brake system and, accordingly, the safety of the car largely depend on it. When the driver presses the pedal, the brake fluid, which is under pressure in the system, transfers force to the caliper piston, and the piston to the pads. The brakes are applied and the car stops. But due to the friction that occurs in this case, the liquid is heated. If it boils, it will lose its important property - incompressibility. In this case, the system will practically stop responding to pressing the pedal and it will be very, very difficult to stop, since the force is not transmitted to the brake pads.
Basic properties of brake fluid
Brake fluids have a number of characteristics that directly affect their performance. This:
- hygroscopicity;
- pour point;
- aggressiveness.
The ability of a liquid to absorb moisture depends on the level of hygroscopicity. The lower this figure, the better. This is due to the fact that moisture, getting into the brake fluid, worsens its properties, in particular, lowers the boiling point.
The aggressiveness of the brake fluid determines the extent to which it has a negative effect on gaskets and other elements of the system made of rubber or plastic.
The pour point is an extremely important parameter. In severe frosts, the brake fluid can become extremely thick, it stops circulating in the system. In this case, it is difficult for the driver to press the brake pedal, and he may have serious problems with driving safety. In Russia, which is famous all over the world for its cold winter, it is necessary to use a liquid that retains its properties even at low temperatures.
Types of fluid for the brake system
There are several classifications of brake fluids, but the most popular today is the one developed by the US Department of Transportation (USDOT). According to it, all products belonging to this category are divided into several classes, from DOT-1 to DOT-5. The most important thing to know about them:
- DOT-1 and DOT-2 fluids are practically not used today;
- DOT-3 is a glycol-based brake fluid, relatively aggressive towards paintwork and rubber products, with a high level of hygroscopicity, with a boiling point of 205 degrees Celsius (provided that moisture has not entered it);
- DOT-4 - this category includes glycol-based brake fluids that corrode paint, but do not adversely affect rubber products; they are less hygroscopic than DOT-3 products and boil at 230 degrees Celsius (provided they have not absorbed water);
- DOT-5 is a more modern type of brake fluid, which uses silicone with a package of additives as a base, due to which it practically does not absorb water, is safe for paintwork and rubber parts, and boils at a temperature of 250 degrees Celsius;
- DOT-5.1 is a glycol-based brake fluid with a relatively high level of hygroscopicity, aggressive towards paintwork, but safe for rubber parts, boiling at a temperature of 275 degrees Celsius (provided that it has not absorbed water).
Within each category, there may be products with improved characteristics, although the official classification does not provide for them. For example, in addition to DOT-4 brake fluid, you can find DOT-4.5 and DOT-4 SUPER. Also, each type, except for DOT-5, is divided into two groups:
- for cars with ABS (in this case, the marking looks like this - DOT-4 / ABS);
- for vehicles without ABS.
Brake fluids belonging to different classes, as a rule, have a different color. This allows the driver to visually determine which product he is dealing with, avoiding mistakes or accidental mixing:
- DOT-3, DOT-4, DOT1 - yellow (from light yellow to light brown);
- DOT-5 - red or pink.
Since DOT-3, DOT-4 and DOT-5.1 brake fluids are glycol-based, they can in principle be mixed. However, different manufacturers may use different additive packages; therefore, according to experts, it is allowed to combine products created by one manufacturer. For example, you can mix Liqui Moly brake fluid with other similar products from the same company. Accordingly, silicone-based DOT-5 products are not compatible with DOT-3, DOT-4, and DOT-5.1.
DOT-3 brake fluid is considered the most versatile and affordable in terms of cost today. Most often it is used in cars and trucks of early years of production, which are not used very intensively.
DOT-4 is a versatile but slightly more expensive product. It is suitable for almost any vehicle with disc brakes, and due to its high viscosity, it works well in systems with a high degree of wear, allowing you to not be afraid of leaks.
DOT 5.1 is a rather expensive product that is well suited for vehicles with low mileage and vehicles that operate in high and even extreme humidity conditions.
When choosing a brake fluid, you must be guided by the following parameters:
- manufacturer's recommendations;
- mileage, condition of the brake system,
- type, weight, power characteristics of your vehicle.
Brake fluid (TF) is a technical component of hydraulic systems that transfers pressure from the master brake cylinder to the drum or disc brake pads. The chemical composition of the brake fluid determines the physicochemical and performance properties of the product. Consider the main components of this composition and its purpose.
Brake fluid - percentage composition
High fluidity, thermal stability, lubricity and anti-corrosion properties are provided by 3 components:
- Solvent
It is a mixture of polyesters of glycolic and boric acids. Provides uniform distribution of chemical compounds in a 3-component mixture. The percentage is 60–90%.
- The basis
Consists of polyglycols (polymerization products of dihydric alcohols with oxides of ethylene, propylene). Reduces friction of rubbing mechanisms and prevents abrasion of metal surfaces of brake pads. Content - up to 30%
- Additives
To improve the technical properties, additives with a mass fraction of 2–5% are added to the brake fluid. Anticorrosive additives prevent oxidative destruction of copper, steel, brass coatings. Antioxidant reagents inhibit the breakdown of polyglycol ethers and reduce the formation of degradation products (acids and resins). Bisphenol A (diphenylolpropane), azimidobenzene and triazoles are used as such additives. The introduced additives prolong the service life of the product.
For acid-base stability, a buffer solution is additionally added to the finished mixture - sodium or potassium salt of boric acid with a fraction<1%.
The composition of brake fluids of different types
The qualitative and quantitative content of the components differs depending on the scope of the TA. Allocate mineral, glycol and silicone compounds.
Mineral compositions- technical liquid of brown color. Castor oil of the general formula C 3 H 5 (C 18 H 33 O 3) 3 is used as a lubricant. The chemical properties of such oils are characterized by temperature lability, a tendency to form coke deposits on brass and copper surfaces. Such qualities were partially leveled by the introduction of benztriazole, trimethylborate and other antioxidant and anticorrosion additives. Due to temperature instability, mineral compositions were used in hydraulic systems with drum-type pads.
Glycolic liquids- traditional compositions containing polyglycol ethers and boric acid polyesters. Glycol TFs are better known by their DOT 3, DOT 5 markings. The ratio of polyglycol ethers and lubricants in combination with environmentally friendly additives meets international quality standards.
silicone fluids- polyorganosiloxanes, which are polymeric organosilicon components, are used as a base. The introduction of a fundamentally new lubricating agent made it possible to achieve complete indifference of TJ in relation to rubber and metals, as well as high fluidity regardless of temperature.
Application rules
Brake fluid produced by various manufacturers has a number of specific requirements, which are indicated in the operating recommendations. There are general rules for the use of TJ. Silicone-based DOT 5.1 formulations are not compatible with glycol counterparts. It is possible to mix different types of TJ provided that the bases are identical. The brake fluid is replaced within the time specified by the manufacturer.
Brake fluid is the most important consumable component in a car system. For what purposes does brake fluid serve, when to replace it and which fluid is better to use, read the article.
Appointment of brake fluids
Transfer force from the master brake cylinder to the wheel cylinders. The task, although narrow, is extremely responsible; the brake system has no right to fail under any circumstances. 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.
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, the most common, including ("Neva", "Tom" and RosDOT, aka "Rosa"), are polyglycols and their ethers. Silicones are used much less often. 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. The 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 “fall through”, 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 prolonged 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 loose 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, not transmitting 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. Brake fluid has one unpleasant property: it absorbs moisture. Due to constant temperature changes, condensate forms and accumulates in it. 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. The presence of only 2-3 percent water in the brake fluid reduces its boiling point by about 70 degrees. In practice, this means that when braking, DOT-4, for example, will boil without warming up to 160 degrees, while in a “dry” (that is, without moisture) state, this will happen at 230 degrees. The consequences will be the same as if air has entered the brake system: the pedal becomes a stake, the braking force is sharply weakened.
Brake Fluid Classes
When developing fluids, as a rule, they are guided by the requirements of the American FMVSS No. 116 (DOT) vehicle safety system. Liquids are classified by boiling point and viscosity (see table), their other properties are similar.
Which TJ should be used in a car is decided by its manufacturer. The brake system of a car (including rubber and structural materials) is developed for a certain type of brake fluids, so domestic fluids should not be used on foreign cars - and not because ours are worse, but imported ones are better. It's just that each machine is made of its own materials, and different TJs can affect them differently. The main rule for using brake fluid is to follow the instructions that came with the car.
DOT 3 fluids are designed for hydraulic drum brakes, as well as for disc brakes under normal operating conditions. DOT 4 fluids are used on vehicles with disc brakes operating in urban areas (in “acceleration-braking” modes). Alcohol-castor liquid "BSK" cannot be considered as a TJ for modern cars. It was developed for old cars of the GAZ-21 era and freezes already at a temperature of -20 ° C. The “Neva” liquid of brand “A” is slightly inferior to the requirements of DOT 3, and brand “B” does not meet them in terms of boiling point, both dry and and moistened fluid. TJ "Neva" was developed for use in the braking systems of the first models of "Zhiguli". Brake fluids DOT 3, "Tom" and DOT 4 can be used on almost all domestic cars. 
DOT5 brake fluid is also known as “silicone” brake fluid. Its advantages: does not corrode paint; does not absorb water and may be useful where absorption is a problem; is compatible with any rubber parts. Disadvantages: DOT5 cannot be mixed with DOT3 or DOT4. Most problems with DOT5 are likely due to mixing with some other type of brake fluid. The best way to upgrade to DOT5 is to completely overhaul the hydraulic system. Complaints about DOT5 causing brake rubber failure were common in early DOT5 formulations. It was believed that the reason for this was the inappropriate use of various additives. In the latest formulas, this problem has been eliminated. Since DOT5 does not absorb water, any moisture present in the hydraulic system will accumulate in one place. This can cause localized corrosion in the hydraulics. Careful bleeding is necessary to remove all air in the system. Small bubbles may form in the liquid, which increase in size over time. Several pumps may be required. DOT5 is somewhat compressive (which gives a subtle "soft pedal" feel). The boiling point of DOT5 is lower than that of DOT4.
DOT5.1 brake fluid is relatively new, so it constantly misleads motorists. This misconception could have been avoided if this brake fluid had been called differently. The designation “5.1” may suggest that this is a silicone-based modification of DOT 5 brake fluid. It would be more natural to call it 4.1. or 6, since DOT5.1 is glycol based, like DOT3 and DOT4, not silicone based, like DOT5. As for the principle nature of 5.1 brake fluid, it can be defined as a “high-tech” DOT4 brake fluid rather than the traditional DOT5. Benefits: DOT5.1 provides superior performance compared to other brake fluids discussed in this article. It has a higher boiling point than DOT3 or 4, both initial and final. In fact, the end boiling point (about 275 degrees C) is almost the same as racing brake fluids (about 300 degrees C), and the initial boiling point of 5.1 brake fluid (about 175-200 degrees C) is naturally much higher than racing brake fluids. liquids (about 145 degrees). DOT5.1 is considered to be compatible with all rubber components.
Disadvantages: DOT5.1 are not silicone brake fluids, hence they absorb water. DOT5.1, like DOT3 and DOT4, will corrode paint. Silicone-free DOT 5.1 fluids are sometimes referred to as DOT 5.1 NSBBF, and silicone DOT 5 to DOT 5 SBBF. The abbreviation NSBBF stands for “non silicon based brake fluids” and SBBF stands for “silicon based brake fluids”.
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 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. 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 Fluid Condition
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 and replacement
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 others. 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. It should be remembered that it is not recommended to mix liquids of different classes and manufacturers, since their properties may change. Do not mix glycol fluids with castor fluids. 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.
brake fluids
Brake fluid is one of the most important operating fluids in a car, the quality of which determines the reliability of the brake system and safety. Its main function is to transfer energy from the brake master to the wheel cylinders, which press the brake linings against the brake discs or drums. 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 (castor), glycol and silicone.
Mineral (castor)- which are various mixtures of castor oil and alcohol, for example, butyl (BSC) or amyl alcohol (ASA) have relatively low viscosity-temperature properties, as they solidify at a temperature of -30 ... -40 degrees and boil at a temperature of +115 degrees.
Such liquids have good lubricating and protective properties, are non-hygroscopic, and are not aggressive to paintwork.
But they do not meet international standards, 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 fluids on a different basis, as swelling of rubber cuffs, components, hydraulic drives and the formation of castor oil clots are possible.
Glycolic brake fluids consisting of an alcohol-glycol mixture, multifunctional additives and a small amount of water. 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). 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 brake fluid "Neva" has a boiling point of at least +195 degrees and is painted light yellow.
Hydrobrake fluids "Tom" and "Rosa" similar in properties and color to "Neva", but have higher boiling points. For the Tom liquid, this temperature is +207 degrees, and for the Rosa liquid, it is +260 degrees. Taking into account hygroscopicity at a moisture content of 3.5%, the actual boiling points for these liquids are +151 and +193 degrees, respectively, which exceeds the same indicator (+145) for the Neva liquid.
In Russia, there is no single state or industry standard that regulates the quality indicators of brake fluids. All domestic manufacturers of TJ work according to their own specifications, focusing on the standards adopted in the United States and Western Europe. (Standards SAE J1703 (SAE - Society of Automotive Engineers (USA), ISO (DIN) 4925 (ISO (DIN) - International Organization for Standardization and FMVSS No. 116 (FMVSS - US Federal Motor Vehicle Safety Standard).
The most popular at the moment are domestic and imported glycol fluids, classified by boiling point and viscosity in accordance with DOT - Department of Transportation (Department of Transportation, USA).
Distinguish between the boiling point of a "dry" liquid (containing no water) and humidified (with a water content of 3.5%). Viscosity is determined at two temperatures: +100°C and -40°C.
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▪ 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.
*Mixing glycol-based brake fluids is possible, but is not recommended as it may degrade fluid performance.
* On vehicles more than twenty years old, the seal rubber may not be compatible with glycol fluids - only mineral brake fluids should be used.
Silicone are 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. But their use is 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").
DOT 5 class fluids are practically not used in conventional vehicles.
In addition to the main indicators - in terms of boiling point and viscosity, brake fluids must meet other requirements.
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.
Impact on metals. 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.
Lubricating properties. The lubricating properties of the brake fluid determine the wear of the working surfaces of brake cylinders, pistons and lip seals.
thermal stability 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.
Hygroscopicity The tendency of polyglycol-based brake fluids to absorb water from the environment. The more water dissolved in TF, the lower its boiling point, TF boils earlier, thickens more at low temperatures, lubricates parts worse, and the metals in it corrode faster.
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. The replacement interval is indicated in the car's operating instructions and usually ranges from 1 to 3 years or 30-40 thousand km.
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. Adding fresh brake fluid when bleeding the system after repair work does little to improve the situation, since a significant part of its volume does not change.
The fluid in the hydraulic system must be completely replaced.
It is necessary to 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 absorb moisture and does not evaporate, in this case the fluid is stored for up to 5 years.
