General information
Brake fluid is an important component of the braking system. Its main purpose is to transfer force from the master brake cylinder to the wheel cylinders.
Since most liquids are practically incompressible, the pressure will be transmitted through the liquid, and after a negligible time will be the same in the entire volume occupied by this liquid. That is, a liquid conducts pressure in much the same way that wires conduct electricity. And since the wires are not made from the first material that comes across, but from the one that is suitable, so the liquid must have certain properties in order to be a good conductor of pressure.
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, so:
1) it must remain a liquid, that is, under operating conditions, it must not boil or freeze;
2) it must retain properties for a long time.
During braking, the brake fluid in the working cylinders heats up to relatively high temperatures. If the temperature reaches the boiling point of the brake fluid, then vapor locks may form in it. At the same time, the brake drive becomes pliable (the pedal fails) and the efficiency of the brakes decreases sharply. This is of particular importance for disc brakes and fast cars.
The main drawback of the currently used brake fluids is hygroscopicity. It has been established that during the year the fluid in the brake system "gains" 2-3% of the water that it takes from the air over time, as a result of which the boiling point drops by 30-50ºC. Therefore, car companies recommend that you change the brake fluid every 2 years, regardless of mileage. The exception is DOT 5.1, it needs to be changed every year, as it is more hygroscopic than the rest.
The main parameter of the brake fluid is its boiling point - the higher it is, the better for the brake system. Boiled brake fluid bubbles and the efficiency of the brake system is reduced - gas bubbles are highly susceptible to compression, so they cannot transfer the braking force to the brake caliper cylinders well.
The brake fluid 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 - 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.
| Standard | Boiling point (fresh / dry) |
Boiling point (old / wet) |
Viscosity at 40 0 Celsius |
Color | The basis |
| SAE J1703 | 205 C | 140 C | 1800 | colorless or amber | ? |
| ISO 4925 | 205 C | 140 C | 1500 | colorless or amber | ? |
| DOT 3 | 205 C | 140 C | 1500 | colorless or amber | polyalkylene glycol |
| DOT 4 | 230 C | 155 C | 1800 | colorless or amber | boric acid / glycol |
| DOT 4+ | 260 C | 180 C | 1200 -1500 | colorless or amber | boric acid / glycol |
| DOT 5.1 | 260 C | 180 C | 900 | colorless or amber | boric acid / glycol |
| DOT 5 | 260 C | 180 C | 900 | purple | silicone |
| Racing Formula DOT 6??? |
310C | 220C | ? | ? | ? |
Basic properties
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.
The operating temperature of the brake fluid ranges from - 50 (on a stationary car in severe frost) to + 150 when driving on mountain roads.
So what happens when the brake fluid boils?
Steam bubbles force some of it into the GTZ expansion tank. The liquid remains in the system, mixed with vapor bubbles. But if the liquid itself is incompressible, then microscopic bubbles just compress well. And now the transmitted pressure will primarily go to compress the bubbles in the entire volume. How it will look for the driver: the brake pedal will become soft, will fail, but there is no braking.
The boiling point of a brake fluid is directly dependent on the water content in it, and decreases with an increase in its concentration. Therefore, the brake fluid must have minimal hygroscopicity (moisture absorption). In addition, moisture in the system contributes to the corrosion of cylinders, and in cold weather - to the formation of ice plugs.
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.
The figure shows the dependence of the boiling point of the brake fluid on the volumetric concentration of water in it.
VISCOSITY
It characterizes the ability of a liquid to be pumped 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.
And what happens if the liquid does not have sufficient frost resistance, that is, it changes its properties dramatically with a decrease in temperature or simply freezes?
In this case, the viscosity becomes the most critical parameter - if it increases, then the brake response time will noticeably increase.
The standard developed by the International Association of Transport Engineers (SAE) explicitly states that the viscosity of brake fluid at -40C should not exceed 1800 cSt (mm 2 / s).
EFFECT 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.
LUBRICANT 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.
The instructions for the car of any manufacturer always indicate that it is compatible with this machine. Of great importance is the composition of the brake fluid. The chemical components of the fluid can affect the brake system in different ways. Incorrectly selected brake fluid can deform the parts of the system and disrupt its operation, up to brake failure.
What is the composition of the brake fluid?
High-quality brake fluid is the key to the perfect operation of the brake system. The main parameters by which quality is determined are:
Boiling temperature. Brake fluid should not boil at relatively low temperatures, because a lot of heat energy is generated during the operation of the brake system. If the liquid boils easily, the resulting vapor bubbles are compressed and interfere with the braking force. And this means that the brakes may stop working.
Viscosity. At low temperatures, the properties of the brake fluid are also very important. It should circulate well through the system. Frozen liquid blocks work, too viscous slows it down, and excessive liquid increases the possibility of leakage;
The main characteristics of the brake fluid are the boiling point, viscosity and hygroscopicity.
Hygroscopicity. The less moisture the brake fluid can absorb, the better. After all, excess moisture is a rapid boiling of a liquid, thickening at low temperatures and another change in its properties. A liquid with changed properties no longer performs its functions and needs to be replaced.
In addition to these characteristics, the anti-corrosion and lubricating properties of the fluid are important - they provide a long life for pistons, cuffs and cylinders. Also, the liquid should not deform the rubber parts of the system.
Can you mix?
It is possible to mix with each other or fill in a new liquid without first cleaning the system in only one case - when glycolic liquids simply belong to different classes (DOT 3, DOT 4 and DOT 5.1). But still, manufacturers recommend mixing liquids of the same class, and even better - of the same brand.
Mineral and glycol fluids do not combine with each other; if they are mixed, the rubber cuffs of the hydraulic drive are deformed. Liquids in which silicone is present are categorically incompatible with any other. Chemical reactions in the case of mixing such fluids with others are aggressive to the details of the system and completely change the properties of the brake fluid.
Reliable operation of the brake system is certainly important for the safety of driving a car, therefore, special requirements are placed on the quality and suitability of the brake fluid. But even if it is of high quality and is chosen correctly, over time its properties will deteriorate during operation, so it is imperative to follow the correct replacement frequency provided by the manufacturer.
When the brake pedal is depressed, the force is transferred hydraulically to the wheel brakes, which slow the vehicle down due to frictional forces. If at the same time the brake fluid can heat up above the permissible limit, boil and form vapor locks. The mixture of liquid and vapor will compress, so the brake pedal may “fall through” and braking will be unreliable, failures may occur. To eliminate this phenomenon in hydraulic drives, special fluids are used for hydraulic drives of the brake system. They are classified by boiling point and viscosity according to DOT (Department of Transportation) standards adopted by the US Department of Transportation. This takes into account the boiling point of a liquid without impurities of moisture (dry), and containing up to 3.5% water. Viscosities - two indicators at a temperature of +100°C and -40°C. See the table below for these figures (according to the US Federal Standard). Similar requirements are imposed by other international and national standards - ISO 4925, SAE J1703 and others. In Russia, there is no single standard regulating the quality indicators of brake fluids, so manufacturers work according to their own specifications.
Application of different classes of brake fluids:
DOT 3 - on relatively low-speed vehicles with drum-type brakes or front disc brakes;
- DOT 4 - on modern high-speed vehicles with disc brakes on all wheels;
- DOT 5.1 - on sports cars, with higher thermal loads. Liquids of this class are practically not used on ordinary cars.
PERFORMANCE REQUIREMENTS
In addition to the main indicators, the boiling point and viscosity, other equally important requirements are imposed on brake fluids.
The liquid must not harm the rubber parts of the car.
Between the pistons of the hydraulic drive of the brakes and the cylinders there are rubber cuffs, the tightness of which increases under the influence of brake fluid. At the same time, rubber compounds increase in volume, expansion up to 10% is allowed. They should not swell too much, shrink, lose elasticity and strength.
Brake fluid must protect metals from corrosion.
Metal components of the hydraulic brake drive can be subjected to electrochemical corrosion. To prevent this process, corrosion inhibitors must be added to the brake fluid, designed to protect steel, cast iron, aluminum, brass and copper parts.
Lubrication of moving parts.
Brake fluid must have lubricating properties to reduce wear on the working surfaces of brake cylinders, pistons and lip seals.
Stability at low and high temperatures.
Brake fluids work in the temperature range from -40 to +100°C. Within these temperature limits, the liquid must retain the properties provided by the manufacturer, with some degree of fluctuation, resist oxidative processes, delamination, the formation of deposits and deposits.
TYPES AND COMPATIBILITY OF BRAKE FLUIDS
Brake fluids are mineral, glycol and silicone based (about 93-98%), with various additives, additives, dyes.
Mineral base is a 1:1 mixture of alcohol, such as butyl, and castor oil. Such a liquid has good lubricating and protective properties, is non-hygroscopic, and does not damage the paintwork. But it has significant shortcomings that do not allow it to meet international standards. Mineral-based brake fluid has a low boiling point, should not be used on vehicles with disc brakes, and a too high viscosity already at -20°C.
Do not mix mineral and glycol fluids. This can lead to excessive swelling of the hydraulic rubber seals and the formation of castor oil clots.
Glycol brake fluids- based on polyglycols and their esters - a group of chemical compounds of polyhydric alcohols. They have a high boiling point, good viscosity and good lubricating properties. The main disadvantage is hygroscopicity, i.e. the ability to take moisture from the air through the compensation hole in the reservoir cap of the main brake cylinder. Moisture saturation reduces the boiling point of the glycol fluid, increases viscosity at low temperatures, reduces lubricity and corrosion resistance. All glycol fluids, both imported and domestic, DOT 3, DOT 4 and DOT 5.1 classes are interchangeable, they can be mixed, but this is not recommended. This can lead to deterioration of their basic properties.
On fairly old vehicles, over 20 years old, the rubber seals may not be compatible with glycol. Only mineral brake fluids can be used here, otherwise it will lead to the destruction of the cuffs.
Silicone brake fluids are made on the basis of silicon-organic polymeric products. Main advantages: viscosity practically does not depend on temperature, is inert to various materials, is efficient in the temperature range from -100 to +350°С, moisture is not taken from the air. But with all the pluses, such liquids have weak lubricating properties, which limits their use. Silicone fluids do not mix with others.
DOT 5 silicone based fluids should be distinguished from DOT 5.1 polyglycol fluids, similar names can lead to confusion. Usually on the packaging they additionally indicate:
DOT 5 - SBBF ("silicon based brake fluids" - silicone brake fluid).
DOT 5.1 - NSBBF ("non silicon based brake fluids" - non-silicon).
CHECK AND REPLACE
Most modern vehicles use glycol brake fluids, which have a number of advantages. But, unfortunately, in a year, glycol will take up to 2-3% of moisture from the air, and the fluid has to be changed periodically, and in advance, while it began to pose a danger to the reliable operation of the brake system. (see pic). Replacement periods are usually indicated in the car's operating instructions, which range from 1 to 3 years.
It is possible to give an objective assessment of the properties of the brake fluid only in laboratory conditions, therefore, to save time, the condition of the brake fluid is assessed visually. Its transparency, uniformity, absence of sediment are evaluated. There are also devices for determining the boiling point of the brake fluid and the degree of its moisture.
Since the liquid does not circulate in the system, its condition in the tank (test point) may differ from that in the wheel cylinders. In the tank, it can pick up moisture from the air, but not in the brake mechanisms. But there the liquid heats up more strongly, sometimes excessively, and its properties may deteriorate.
If you simply add new brake fluid when pumping the system after repair work, then this will practically not fix the situation, a significant part of the volume will not change.
The fluid needs to be completely changed. The sequence and features of replacing the brake fluid, for example, when pumping with the engine running, depends on the design of the brake system (type of booster, availability of anti-lock devices, etc.). This information can be found in the vehicle's owner's manual.
On domestically produced vehicles, brake fluid is replaced as follows:
Method 1. The old fluid is completely drained by opening all valves (fittings) for releasing air from the hydraulic brake drive. Then the tank is filled with new fluid and, pressing the brake pedal, it is pumped into the system. In this case, the valves must be sequentially closed when liquid appears from them. Then you need to remove air from each hydraulic circuit (“bleeding” the brakes). When using this method, the new liquid does not mix with the old. Part of the new fluid released during pumping can be used again, after allowing it to settle and filtering.
Note. Before replacement, a drain hose is put on each valve, the other end of which is lowered into a suitable container. In this way, it is possible to prevent damage to tires and paintwork on suspension parts, brakes by leaking brake fluid.
Method 2. Constantly topping up the tank of the main cylinder with fresh liquid, each circuit is pumped in turn, thus displacing the old liquid and preventing the system as a whole from draining. This is done until new fluid appears from the valve. The advantage of this method is that air does not enter the hydraulic drive, which makes control pumping unnecessary. But at the same time, it is not excluded that part of the old liquid will remain in the system. In addition, a larger amount of fresh fluid will be required than with the first method, since most of it removed from the hydraulic drive mixes with the old one and becomes unsuitable for further use.
SAFETY PRECAUTIONS FOR HANDLING BRAKE FLUID
Any brake fluid, regardless of type, is stored only in sealed containers, without contact with air, to prevent its oxidation, moisture accumulation and evaporation.
Remember that brake fluid is usually flammable or flammable. It is strictly forbidden to smoke while working with it. It is poisonous, if ingested, even 100 ml, can be fatal. Brake fluid usually smells like alcohol and can easily be confused with an alcoholic beverage. If you accidentally swallow liquids, for example when pumping out of the reservoir of the master cylinder, you should immediately flush the stomach. In case of contact with eyes, rinse with plenty of water. In any case, in such situations, you should consult a doctor.
GENERAL INFORMATION
When you press the brake pedal, the force is transferred by means of a hydraulic drive to the wheel (working) brake mechanisms, which 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 manufacturers work according to various technical conditions.
Brake fluids of various classes are mainly used:
- 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 the main indicators - they have a low boiling point (they cannot be used on machines with disc brakes) and become too viscous even 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 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. 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 - leaking brake fluid can damage tires and paintwork 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.
Brake fluid is exactly the substance thanks to which we are safe while driving. This is the reason for the high demands on the quality of the brake fluid.
Can you mix brake fluid?
Indeed, in addition to affecting the main components and mechanisms of the brake system, the brake fluid must: not destroy this very system (metal and rubber-plastic products) and remain effective in its main parameters for a sufficient time.
Before we consider the composition and the various requirements for it, we will answer a question that always worries motorists, especially beginners.
Basically, you can. But! Only if the liquids are on the same basis. This information is located on the label. If there is no such information, then there is no need to take risks. In this case, be sure to familiarize yourself with such a parameter as the operating temperature of the TJ. If it’s already “impatient”, then at first it is recommended to make a trial mixing of different TJs, outside the capacity of the brake system. Mix and then, only to get to the service.
In general, it’s better not to take risks and always fill the brake reservoir of your car with exactly the same TJ recommended by the manufacturer. Today this is no problem. TJ for every taste and every budget.
Information for thought. Silicone TJs cannot be combined with TJs on a different basis. Mineral TA cannot be combined with glycolic. Imported and domestic glycol TA DOT3;4;5,1 are interchangeable, but mixing them is still not recommended.
What is brake fluid for?
Therefore, modern brake fluids are classified by boiling point and viscosity according to DOT standards. In addition to DOT, there are also generally accepted standards: ISO 4925, SAE J 1703, etc.
Classes of brake fluids according to traditional use:
- DOT3 - for standard classic cars with front disc brakes and rear drum brakes.
- DOT4 - for modern cars with disc brakes on both axles.
- DOT5.1 - on sports cars where the temperature loads on the brakes are very high.
Requirements for brake fluids in production
In addition to a certain operating temperature, TJ must comply with many indicators. These performance requirements are checked either in the laboratory or at the service using equipment - a refractometer (brake fluid tester). They check the density of the brake fluid in terms of the presence of moisture in the composition of the brake fluid.
In addition, the TJ must meet the following parameters:
- The impact on the rubber parts of the brake system should be kept to a minimum. In the process of contact of rubber cuffs and TJ, excessive swelling or shrinkage of rubber goods should not occur (tolerance no more than 10%).
- Anti-corrosion properties of TJ. After all, the brake system contains parts made of various metallic materials. A “golden” mean must be found in the TJ in order to prevent corrosion of any of them. As a rule, brake fluid is considered to be of high quality, which includes corrosion inhibitors, for simultaneous protection of: steel, copper, brass, cast iron, aluminum.
- The lubricating properties of TJ directly affect the wear of the working surfaces of pistons and brake cylinders.
- TJ stability at low and high temperatures. An important quality when operating in climatic zones with different temperature conditions. TJ at - 40 and at +100 should retain its original performance properties.
Composition of brake fluids
Glycolic brake fluids. Based on polyglycols and their esters. It is a TF with a high operating boiling point and good viscosity. The disadvantage of glycol brake fluids is hygroscopicity - they tend to absorb moisture from the atmosphere.
Silicone brake fluids. They are based on organosilicon polymers. Positive qualities: wide temperature range - 100 + 350°C, inertness to various materials, low hygroscopicity. But, they have insufficiently high lubricating properties.
The order and frequency of replacing the brake fluid, as a rule, is indicated in the vehicle's operating manual. On average, this figure ranges from 1 to 3 years.
Good luck choosing the right brake fluid for your vehicle.
