Currently, several brands of brake fluids are produced, which are divided into liquids for mass and special purposes. The first include BSK, Neva, Tom and Rosa, the second - GTZh-22M.
BSK liquid (TU 6-10-1533–75) is a mixture of butyl alcohol, refined castor oil and a red organic dye. It has good lubricating properties, but low viscosity-temperature characteristics, since at -20 ºС castor oil precipitates, which can lead to breakdown of the brake system. In addition, it is corrosive and aggressive to copper and brass. Due to the low boiling point of the BSC liquid (117 ° C), during the summer period of operation, “vapor locks” can form in the hydraulic brake drive, so it can only be used on older car models and agricultural machinery, i.e. those in brake systems which used elements of non-oil resistant rubber.
Liquid "Neva" (TU 6-01-1163-78) - the main components are glycol ether (ethyl carbitol) and polyester (polyoxyl propylene glycol); contains anti-corrosion additives. The liquid is efficient at temperatures up to -40 ºС. Designed for hydraulic brakes and clutches of trucks and cars that operate in a temperate climate zone. When moistened, it has a low boiling point and is corrosive to metals.
Fluid "Tom" (TU 6-01-1276-82) was developed to replace the fluid "Neva". The main components are concentrated glycol ether (ethyl carbitol), polyester, borates (to improve performance) with the addition of thickeners; contains anti-corrosion additives. It has better performance properties than "Neva", a higher boiling point (200 ºС). Compatible with the "Neva" when mixed in any ratio.
Rosa liquid (TU 6-05-221-569-87) was developed for new models of cars and trucks. The main component is boron-containing polyester; contains anti-corrosion and antioxidant additives. The liquid has a high boiling point (260 ºС) and a "wetted" liquid boiling point (165 ºС). This ensures reliable operation of the brake system under severe operating conditions and allows you to increase the service life of the fluid. Rosa brake fluid is compatible with Tom and Neva fluids.
Liquid GTZh-22M (TU 6-01-787-75) consists of a mixture of glycols (diethylene glycol and ethyl cellosolve), water and anti-corrosion additives. Painted green. In terms of performance, it is close to the Neva, but has worse anti-corrosion and viscosity-temperature properties (at 50 ºС, the viscosity ranges from 7.9 to 8.3 mm 2 / s. It loses mobility at -50 ºС). It is recommended for use in all climatic zones, except for the Far North all seasons.
Liquids "Neva", "Tom", "Rosa" are compatible, their mixing with each other is possible in any ratio. Mixing these liquids with BSC is unacceptable, as it will lead to separation of the mixture and loss of the necessary performance properties.
Abroad, a number of regulatory documents apply to brake fluids, namely: SAE J 1703 standards (developed by the International Association of Transport Engineers), FMVSS 116 (developed by the US Federal Motor Vehicle Safety Society), ISO 4925. Among them, the most widely used standards are DOT ( Department of Transportation), which are presented in Table 3.7.
Table 3.7 – Characteristics of brake fluids
For passenger cars, depending on the design, technical characteristics and year of manufacture, fluids that meet the requirements of DOT-3, DOT-4 and DOT-5 are used. DOT-5 standards are met by the most modern fluids designed for high-speed and sports cars.
Table 3.8 shows the performance of the main brands of fluids for vehicle brake systems.
In addition to standard glycol fluids, mineral oil based fluids (ISO 7308) and silicone fluids (SAE J 1705) are available.
The use of liquids based on mineral oils makes it possible not to lower the boiling point, since they are not hygroscopic. Special additives are added to the brake fluid to ensure that the temperature dependence of viscosity is as low as possible.
Silicone fluids also do not absorb moisture, but their disadvantage is high compressibility and poor lubricity, which limits their use. An undesirable consequence of the use of silicone fluids and mineral oils is the accumulation of free water, which evaporates when the fluid is heated above 100 ºС and freezes when it is cooled below 0 ºС, with the subsequent formation of bubbles that prevent the normal operation of the brake system.
Table 3.8 – Characteristics of the main brands of brake fluids
| Index | BSC | ""Neva"" | "Tom" | ""Dew"" |
| Appearance | Transparent homogeneous liquid | |||
| red color without sediment and mechanical impurities | from light yellow to dark yellow without sediment, slight opalescence is allowed | from light yellow to light brown without sediment | ||
| Kinematic viscosity, mm 2 /s: -40 ºС, not more than 50 ºС, not less than 100 ºС, not less | 2500 * (130 (0 ºС)) 9.4–13 5.5 (70 ºС) | |||
| Boiling point, ºС, not lower | ||||
| Boiling point of "moistened" liquid, ºС, not lower | – | 138 * | 165 * | |
| Stability at high temperature, ºС, no more | – | |||
| Change in the volume of rubber after aging in the brake fluid,%: 51-1524 7-2462 | – 5–10 | 2–10 2–10 | 2–10 2–10 | 3–12 2–8 |
| Change in the weight of the plates, mg/cm 2 , not more than: tinplate steel aluminum alloy cast iron brass, copper | 0,2 0,2 0,1 0,2 0,4 | 0,2 0,2 0,1 0,2 0,5 | 0,1 0,1 0,1 0,1 0,4 | 0,2 0,2 0,1 0,2 0,4 |
| Pour point, ºС (loss of mobility) | –20 | -60 (does not lose) | -60 (does not lose) | –60 |
| Hydrogen ion concentration pH | 6,0 | 7,0–11,5 | 7,0–11,5 | 7,0–11,5 |
| * Factual data. |
Foreign analogues of liquids "Tom" and "Neva" are liquids corresponding to the international classification DOT-3, which have a boiling point of more than 205 ºС, and for liquid "Rosa" - liquids DOT-4 with a boiling point of more than 230 ºС.
Brake fluid "NEVA" TU 6-01-34-93
Brake fluid "NEVA" is the first domestic brake fluid developed by JSC "Plant named after Shaumyan" more than 25 years ago in accordance with the international classification (class DOT-3), for use in vehicles mastered under license from AvtoVAZ (Togliatti) .
Brake fluid "NEVA" consists of a multi-component mixture containing a base in the form of ethyl carbitol and several anti-corrosion additives. The composition is protected by copyright N364228.
brake fluid "NEVA" is efficient up to a temperature of minus 40-45? It has high anti-corrosion properties and good compatibility with rubber products. Brake fluid "NEVA" is used in the hydraulic drive of brakes and clutches of cars and trucks of all brands except for GAZ - 24 release until 1985. Brake fluid "NEVA" is fully compatible with the brake fluid of a later development: "Tom" and "Rosa". Depending on the operating conditions, the service life of the brake fluid "NEVA" is 1-2 years.
Brake fluid analogues "NEVA": Shell Donax B, Castrol Brake Fleud HD, etc. fluids belonging to the DOT-3 class of the international classification of brake fluids.
Specifications:Appearance and color transparent, homogeneous liquid from light to dark yellow without sediment. Opalescence allowed
Kinematic viscosity mm/s
at 100°C, not less
at a temperature of 50°C, not less than
at minus 40°C less
Boiling point, °C not lower than 195
Boiling point of "humidified liquid", °C, not lower than 138
Stability at high temperature, °C, no more than 5
brake fluids produced on the basis of castor oil or on the basis of glycols. A good petroleum-based brake fluid, GTN fluid, has been developed and tested. However, this fluid has not yet found application, since the rubber parts of automotive brake systems are made from ordinary non-oil resistant rubber. Such parts, upon contact with the oil liquid, quickly swell and become unsuitable for further operation.
Good performance properties were shown by castor-based brake fluids. Castor oil has high lubricating properties and does not cause swelling or softening of natural rubber and brake system seals made from it.
When mixing 60% isopentanol and 40% castor oil, ASA brake fluid is obtained, when 50% butanol and 50% castor oil are mixed, BSC brake fluid is obtained, when 40% ethanol and 60% castor oil are mixed, ESC brake fluid is obtained. ESC fluid has a number of disadvantages and is produced and used in limited quantities. Ethanol boils at 78 degrees. C and at high temperatures can produce vapor locks in the brake system.
All castor brake fluids are prepared by mixing only with concentrated alcohols. The ingress of water into the liquid leads to a decrease in the concentration of alcohol, which causes stratification of the liquid. Alcohol-castor mixtures have a rather low pour point, however, already at a temperature of minus 20 degrees. With intensive crystallization of the components of castor oil. Therefore, castor brake fluids at temperatures below minus 20 degrees. Not recommended for use.
In recent years, various mixtures of glycols and their derivatives have been increasingly used as brake fluids. A mixture of glycols with a complex of anti-corrosion and anti-wear additives is produced and used under the brand name GTZh-22M hydraulic brake fluid.
Formulas have been developed and industrial production of brake fluids "Neva" and "Tom" has been organized, which are compositions based on ethyl carbitol with various thickeners and anti-corrosion additives.
Liquids based on glycols and ethyl carbitol are superior in many properties to alcohol-castor mixtures. They have good low temperature properties (do not freeze at minus 60 degrees C), low volatility and high flash point. All of these fluids are neutral with respect to rubber non-oil resistant parts, so they can be poured into the brake system of cars with conventional rubber seals. Unlike the previously used GTZh-22 fluid, when using GTZh-22M, Neva and Tom fluids, it is not necessary to pre-lubricate the rubbing parts of the brake system with castor oil or alcohol-castor liquid BSK when preparing cars for the spring-summer and autumn-winter operation. These liquids should not be mixed with castor alcohol liquids, as separation and loss of castor oil occurs. The use of liquids based on glycols and ethylcarbitol ensures the operation of the hydraulic brake drive at ambient temperatures from + 50 to - 50 degrees. C. All of these fluids are toxic, so care must be taken when handling.
Classification of car braking techniques
Distinguish service, emergency and emergency braking.
Service braking (with a deceleration rate of less than 3 m/s2) is not associated with a shortage of time to slow down or stop the vehicle, and under normal driving conditions is the most acceptable, as it is carried out in a comfortable zone of negative accelerations.
Emergency braking is used in critical situations associated with a shortage of time and distance. It implements the most intense deceleration, taking into account the braking properties of the car, as well as the driver's ability to apply traditional or non-traditional methods, depending on the tire grip coefficient and other external conditions.
Emergency braking is used in case of failure or failure of the service brake system and in all other cases when this system does not achieve the desired effect.
Impulse vehicle braking
Impulse braking includes two methods - intermittent and stepped.
Intermittent braking - periodically depressing the brake pedal and releasing it completely. The main reason for temporarily stopping the action of the brake mechanisms is the blocking of the wheels. This method is used on rough roads and where sections with different coefficients of adhesion alternate, for example, asphalt with ice, snow and mud. Before hitting a bump or slippery area, fully release the brake.
The effectiveness of the intermittent method during emergency braking is insufficient, since the temporary cessation of the brakes affects the increase in the braking distance of the car.
For emergency braking, a stepwise method is characteristic, which outwardly resembles intermittent, but, unlike intermittent braking, does not have a passive phase associated with the complete cessation of the braking mechanisms. It is characterized by a consistent increase in each subsequent effort on the brake pedal, as well as the time of its application. The first pressing on the pedal should be extremely short and weak. Overbraking in one of the stepped braking pulses requires its own compensation, which manifests itself in an increase in the time to unlock the wheels. In addition, braking with repeatedly repeated short-term blocking of the wheels requires additional compensation for vehicle stability using steering.
Emergency vehicle braking
The advent of ABS, ESP and other driver assistance systems during braking is changing our understanding of what to do during emergency braking. However, for owners of cars not equipped with ABS, the old recipes are still true.
The intensity of emergency braking is limited by the capabilities of the driver (mastery of technical techniques and the ability to maintain stability and controllability of the car), the car (the effectiveness of braking systems, the quality of tires) and external conditions (coefficient of adhesion of tires to the road, terrain). In addition to reducing speed, emergency braking also has actions that allow you to control the stability and controllability of the car.
Control over the implementation of braking on the verge of blocking the wheels is carried out using the so-called "muscle feeling". Different drivers have significant differences in the ability to adjust muscle efforts during emergency braking. Another complicating factor is the "fear mechanism" that can inhibit even automated motor skills and impair motor coordination. The most pronounced manifestation of the "mechanism of fear" is braking in a critical situation with completely locked wheels. It is necessary to suppress this manifestation of reflex activity in the form of dosing efforts depending on the speed of the vehicle, the coefficient of adhesion, road surface, and motion geometry.
In most cases, the use of emergency braking is associated with the effect of complete or partial short-term blocking of the wheels. Most often, blocking occurs on the rear wheels of the car, since when braking, the load in the car is redistributed along the axles: the front wheels are loaded, and the rear wheels are unloaded. Therefore, many cars have special brake force regulators that weaken the effect of the rear brakes on an unloaded car.
An unconventional way of braking is side slipping, which can be implemented with the rear axle skidding, with the drift of all axles or with the rotation of the car. To transfer the car into a critical skid of the rear axle, momentary switching on / off of the parking brake on the turning arc or shock switching on a downshift is used. In this case, the front wheels are controlled (static friction), while the rear wheels are not (sliding friction, or "skid"). For stable braking in a skid, the driver uses compensatory steering and variable throttling.
The "gas-brake" technique is extremely effective on vehicles with front-wheel drive and allows you to maintain controllability of the front wheels with intensive braking with a service brake, avoid blocking the steered wheels, and increase the braking force. Braking is performed with the left foot, during braking the right foot continues throttling - open throttle.
Engine braking and gear shifting
Engine braking does not provide much of a deceleration effect in its purest form and is therefore often ignored by drivers. However, its significance is essential when driving a car in conditions of a low friction coefficient and allows you to increase the stability and controllability of the car, its stability during emergency maneuvers.
Safe driving requires that any braking technique be performed in a combined way, i.e. with the transmission on. Braking in neutral under normal conditions should be regarded as a frivolous act, and under difficult conditions as a dangerous one. Some novice drivers have developed a reflex: when starting to slow down, be sure to turn off the clutch. At the heart of this habit is the student's fear of turning off the engine. But the engine stalls at a shaft speed of less than 500-700 rpm. This mode in direct gear corresponds to a speed of 13-15 km / h, so you should turn off the clutch almost before the car stops.
Reception "regassing" is performed to equalize the circumferential speeds of rotation of the gears involved. This technique helps to avoid a jerk of the car and not to provoke a skid on a slippery road, and, in addition, reduces the wear of the synchronizers and increases the life of the gearbox. At the same time, the right foot of the driver performs active braking by the service brake, therefore, in order to perform gas retraction, it is necessary to temporarily stop active braking or re-gas it with the toe (heel) of the right foot without interrupting braking.
Regassing during service braking is performed in three cycles: disabling the overdrive; pause in the neutral position and regassing; downshifting.
Emergency braking requires successive downshifts from direct to 2nd gear. First gear can be engaged in emergency mode if the service brake system fails. In this case, it is desirable to reduce the time for regassing and change the structure of the reception. Increasing the engine speed is achieved not by a separate press on the fuel control pedal, but by slow disengagement of the clutch at open throttle.
Selectivity is very harmful: on a dry road, brake only with a service brake, on a slippery road - also with a motor. It is much safer to have a developed skill of mixed braking and apply it in any conditions than to create a stereotype of "summer" braking for yourself and use it on ice or snow due to the existing automatism.
Emergency braking of the car
Emergency braking can be carried out by a parking brake, as well as by non-traditional methods, including the contact method using natural and artificial obstacles.
In an emergency, when all the possibilities of making an emergency maneuver have been exhausted and / or the brake system has failed, most drivers stop driving due to inability and stress. However, the passive safety of the design of a modern car can significantly reduce the severity of the consequences of an accident due to the deformation of collapsible parts of the body, such as fenders, bumpers, trunk.
In this case, it is important to choose the direction of contact in order to avoid a head-on impact, since of all the power elements of the body, the side members have the maximum longitudinal rigidity, departure into the oncoming traffic lane and overturning. Both the driver and passengers need to be able to quickly assume a safe posture to reduce the effects of an impact.
The main task of the brake fluid is to transfer energy along the route "brake master cylinder - wheel cylinders", thanks to which the brake linings tightly wrap around the discs (drums).
The pressure in the hydraulic drive of the brakes can be 10 MPa, and the temperature level of the brake fluid in the disc brakes reaches 150-190 °C. As a result of permanent temperature fluctuations, water enters the brake system through rubber seals. This leads to the fact that the "tormozuha" is saturated with water, which reduces its boiling point.
It is very dangerous if during operation the boiling point of the brake fluid drops below 150 ° C - in this case, at high speed and sudden braking, there is a danger of the liquid "boiling", bubbles (gas, steam) appear in it, vapor locks form, and this is fraught with failure brakes at the right time.
The boiling point of the brake fluid is an indicator of the maximum operating temperature of the hydraulic brake actuator.
During operation, due to the action of water, the boiling point of the brake fluid decreases successively, so that two parameters are set: the boiling point of the "dry" brake fluid, as well as the boiling point of the "watered" fluid (the presence of water -3.5%).
What will the boiling point of a "watered" liquid give us? The approximate temperature of the "boiling" of the liquid after 2 years of its operation in the hydraulic brake drive.
The trend of recent years is to improve the quality of brake fluid by increasing the boiling point.
This can be seen in the table.
Boiling point of brake fluids
Brake fluids must have high viscosity-temperature properties, protect against corrosion, lubricate and be well compatible with seals, maintain their qualities at high / low temperatures.
Today's brake fluids are the result of blending esters with low molecular weight polymers and anti-corrosion and antioxidant additives.
Brake fluid "Neva"- based on ethyl carbitol, in its composition it contains a thickening and anti-corrosion additive. Operating temperature level -40...+45 °С. Used in the hydraulic drive of brakes and transmissions of old cars (until 1985 onwards). Service life - 1 year.
Brake fluid "Tom" made as a replacement for the "Neva". A mixture based on ethyl carbitol and boron-containing polyester, has a thickening and anti-corrosion additive in its composition. Possesses more perfect, in comparison with "Neva" working properties, the increased boiling point. Perfectly compatible with the "Neva".
Operating temperature from -40 to +45 °С. Used in the hydraulic drive of brakes and transmissions of all models of trucks and cars, except for cars with front-wheel drive. The working period of the liquid "Tom" is 2 years.
Brake fluids "Rosa DOT-4", "Rosa" and "Rosa-3"- high-temperature compositions based on boron-containing polyester, contain antioxidant and anti-corrosion additives.
Quite rarely, there are liquids "Rosa" and "Rosa-3", which have plasticizers in their composition. These liquids have a high boiling temperature level (+260 °C) and a boiling point of the "watered" liquid (+165 °C). They operate at an air temperature of -40 to +45 °С. They are used in brake systems of trucks and cars.
Good compatibility with brake fluids "Tom" and "Neva". Operable for 3 years.
Brake fluid BSK- the result of mixing castor oil and butanol. Thanks to an organic dye, it has an orange-red color. Operating temperature range -20 to +30 °С. They are used in the hydraulic drive of brakes and transmissions of old cars.
Characteristics of brake fluids
|
Indicators |
Rosa, Rosa-3, Rosa DOT-4 |
|||
|---|---|---|---|---|
| Appearance | Transparent homogeneous liquid from light yellow to dark yellow without sediment. Slight opalescence allowed | Transparent homogeneous liquid of orange-red color | ||
| Kinematic viscosity, mm 2 / s, at a temperature: 50 °С, not less |
5,0 | 5,0 | 5,0 | 9,0 |
| 100 °С, not less | 2,0 | 2,0 | 2,0 | - |
| -40 °С, no more | 1500 | 1500 | 1450 | 2500 |
| Low temperature properties: appearance after exposure (6 h, -50 °С) |
Clear liquid without segregation and sediment | |||
| Travel time air bubble through layer liquids at overturning vessel, with no more |
35 | 35 | 8 | - |
| Boiling temperature, °С, not lower |
195 | 220 | 260 | 115 |
| Boiling temperature "moisturized" liquid, at least |
138 | 155 | 165 | 110 |
| Content mechanical impurities, % |
Absence | |||
| pH | 7,0-11,5 | 7,0-11,5 | 7,5-9,0 | >=6 |
| Interaction with metals: change plate weights, mg/cm 2 , no more tinplate |
0,1 | 0,1 | 0,1 | 0,2 |
| steel 10 | 0,1 | 0,1 | 0,1 | 0,2 |
| aluminum alloy D-16 |
0,1 | 0,1 | 0,1 | 0,1 |
| cast iron SCH 18 | 0,1 | 0,08 | 0,1 | 0,2 |
| brass L62 | 0,4 | 0,1 | 0,2 | 0,4 |
| copper M1 | 0,4 | 0,2 | 0,2 | 0,4 |
| Impact on rubber, %: change rubber volume brand 7-2462 at 70 °С |
2-10 | 2-10 | 2-10 | 5-10 |
| the same, brands 51-1524 at 120 °C |
2-8 | 2-10 | 2-10 | - |
| limit change strength rubber brand 51-1524, %, no more |
20 | 18 | 25 | - |
| Note. Liquids "Neva", "Tom", "Rosa" and its modifications are compatible, their mixing with each other is possible in any ratio. Mixing of these liquids with BSC is unacceptable. | ||||
As for vehicles operating in the northern regions, a liquid with a kinematic viscosity of at least 1500 mm 2 / s (at -55 ° C) is required. But there are no such liquids on the domestic market, so the Neva and Tom liquids are diluted with 18-20% ethyl alcohol. This mixture can work down to -60 °C, but its boiling point is low. So they dilute the liquid with alcohol forcibly, and this mixture must be replaced before winter.
Foreign analogues of "Neva" and "Tom" are DOT-3 liquids (boiling point over 205 °C), and analogues of Rosa liquid are DOT-4 liquids (boiling point over +230 °C).
shock absorber fluids
Automotive shock absorbers are needed to reduce body vibrations on elastic suspension elements. Thanks to them, the ride of the car remains smooth even while driving on bad roads. Where do shock absorbers work? In hydraulic shock absorbers of lever-cam and telescopic type and in telescopic racks.
The main criterion for shock absorber fluids is kinematic viscosity. Say, at -20 °C, the viscosity should not be more than 800 mm 2 / s. If the viscosity increases, then the work of the shock absorbers becomes more difficult, which causes the suspension to lock up.
The main qualities of shock absorber fluids are: lubricity and low foaming.
If these conditions are met, shock absorber wear is minimized. Other important qualities of shock absorber fluids will be oxidation resistance, volatility, compatibility with rubber seals.
By their composition, shock absorber fluids are a low-viscosity petroleum base, which includes the following additives - viscous, depressant, antioxidant, anti-wear, dispersant and anti-foam.
AZH-12T, GRZH-12 and MGP-12
Shock-absorbing liquid АЖ-12Т It is produced by mixing petroleum oil and polyethylsiloxane fluid containing anti-wear and antioxidant additives. It is used in shock absorbers of trucks and special equipment.
Shock-absorbing liquid MGP-12 created instead of liquid MGP-10. Low-viscosity low-pour oil base, containing additives: depressant, dispersant, anti-wear, antioxidant and anti-foam.
Used in telescopic struts and shock absorbers of trucks and cars.
Shock-absorbing liquid GRG-12- a product of mixing purified transformer and spindle distillates + a package of additives - depressant, antioxidant, antiwear and antifoam.
It is used in shock absorbers and telescopic struts of cars.
Characteristics of shock absorber fluids
|
Indicators |
|||
|---|---|---|---|
|
Kinematic |
|||
|
50 °С, not less |
|||
|
100 °С, not less |
|||
|
20 °С, no more |
|||
|
40 °С, no more |
|||
|
Temperature, °C: |
|||
|
solidification, |
|||
|
Density at |
|||
|
Stability |
Absence |
||
|
acid number |
|||
|
Absence |
|||
|
Test for |
Withstands |
||
Brake fluid with different bases are incompatible with each other, they separate, sometimes sediment 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 Ros DOT, Neva, Tom, as well as other domestic and imported polyglycol fluids DOT3, 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 dark 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 transparent and there is no sediment, TFs are compatible. It should be remembered that mixing liquids of different classes and manufacturers is not recommended, since their properties may change. Do not mix glycol fluids with castor fluids.
5.3 Marketing retreat
DOT 3, DOT 4 and DOT 5.1 fluids are hygroscopic, which means that they absorb moisture from the air. The presence of moisture in the fluid reduces its boiling point, the operating temperature of the brake disc and pads usually exceeds it. That is why the boiling points of dry liquids and liquids containing moisture are indicated. The boiling point of a wet liquid is measured at a moisture content of 3.5% in it. Hygroscopicity is the reason for replacing the brake fluid at least once every two years. The friction material on the brake pad serves to insulate the caliper from the heat generated by the disc, which is a very heavy warp to replace the pads long before they wear out. DOT5 fluid is not hygroscopic and is not miscible with water. When water enters the system, it sinks down and is located near the hottest area of the system. This means that it will boil very easily and quickly, forming gas bubbles that compress easily, which in turn gives the brakes a springy feel. Another problem with DOT 5 is that the liquid itself becomes compressible as it approaches boiling point; this leads to a feeling of elasticity of the brakes with frequent and prolonged use.
Today in our market you can find a lot of imported brake fluids (Brake Fluid). If such a liquid is recommended by the manufacturer for any cars and is labeled DOT-3 or DOT-4, then it can be used equally in foreign cars and in domestic cars. It can also be argued that the composition of this product includes various esters, and low molecular weight polymers and targeted additives. As for performance (including temperature properties), when compared in the appropriate class (DOT-3 or DOT-4), imported liquids are approximately identical to our Tom or Rose and do not have any special differences from them.
Imported drugs are widely represented on the market. When choosing, the main criterion is compliance with the requirements of the DOT class recommended for a particular vehicle (for the Niva DOT-4).
In my opinion, the use of imported liquids in Niva makes little sense. Corrosion of the brake system is more active outside, and the rest of the properties are identical to Rosa.
And finally, for the most inquisitive, some car companies use brake fluids based on mineral oil. They are not hygroscopic, do not provoke corrosion and will last longer than counterparts with glycol starter. They are very rare and expensive.
When fluid does not leak in the hydraulic brake drive, it would seem that no attention should be paid to it. However, the efficiency of braking and the stability of the system depends on its condition. If, for example, bad antifreeze or engine oil only shortens the life of the engine, then poor quality brake fluid can lead to an accident.
General information
Brake fluid (TF) consists of a base (its share is 93-98%) and various additives (the remaining 7-2%).
Outdated 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 during strong heating, while others protect the metal parts of hydraulic systems from corrosion.
Basic properties of any brake fluid depend on the combination of its components.
- Boiling temperature. The higher it is, the less likely it is that a vapor lock will form in the system. When the car brakes, the working cylinders and the fluid in them heat up. If the temperature exceeds the allowable temperature, the TJ will boil and vapor bubbles will form. The incompressible fluid will become “soft”, the pedal will “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.
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.
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).
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.
In Russia, there is no single state or industry standard that regulates the quality indicators of brake fluids. Domestic manufacturers work according to their own specifications, focusing on the standards adopted in the USA and Western Europe (standards 3 J1703, ISO (DIN) 4925 and FM VSS No. 116). Liquids are classified according to their boiling point and viscosity ( see table), their other properties are close.
Which TJ should be used in a car is decided by its manufacturer. As a rule, DOT 3 class fluids are designed for relatively slow-moving cars with all drum or disc brakes in front. TJ with improved performance characteristics that meet the requirements of DOT 4 are designed for modern cars with improved dynamic qualities. Such machines allow frequent hard accelerations and intense decelerations, and they have predominantly disc brakes on all wheels. DOT 5 class fluids are rarely used, mainly on road sports cars. The thermal loads on the TJ are commensurate with those arising in the hydraulic systems of special racing cars.
Liquids "BSK" and "Neva" (grades A and B) do not meet modern requirements for boiling points, and "BSK" also does not meet low-temperature properties. It freezes already at minus 20°C.
Features of the operation of brake fluids
The absorption of water from the atmosphere is characteristic of polyglycol-based TF. At the same time, their boiling point decreases. FM VSS normalizes it only for “dry” liquids that have not yet collected moisture, and moistened liquids containing 3.5% water - i.e. limits only limit values. The intensity of the absorption process is not regulated. TJ can be saturated with moisture at first actively, and then more slowly. Or vice versa. But even if the boiling point values of “dry” liquids of different classes are made close, for example, to DOT 5, when they are moistened, this parameter will return to the level characteristic of each class. However, in laboratory testing, TF manufacturers usually plot boiling point curves. For each liquid they are different (see figure).
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. 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 4 . Therefore, the FM VSS 116 standard requires that "silicone" liquids be colored deep red. The rest of modern TJs are usually yellow (shades from light yellow to light brown).
For additional verification, you can mix the liquids in a 1:1 ratio in a glass container. If the mixture is clear and there is no sediment, the TAs are compatible.
Replacement. The addition of fresh fluid when pumping the system after repair does not restore the properties of the TJ, since almost half of it remains practically unchanged. Therefore, within the time limits established by the car factory, the fluid in the hydraulic system must be completely replaced. The sequence and features of this operation, for example, pumping with the engine running, depend on the design of the system (type of amplifier, anti-lock devices, etc.) and are known to service station specialists. This information is often found in the vehicle owner's manual.
On domestic cars, the fluid is replaced in one of the following two ways.
- The old TJ is completely drained by opening all the air release valves (fittings) and draining the system. Then fill the tank with fresh liquid and pump it in by pressing the pedal. The valves are sequentially closed when TJ appears from them. Then air is removed from each circuit (branch) of the hydraulic drive.
The disadvantage of this technique is the need for a final (control) pumping of the system. In addition, a drain hose must be put on each valve, lowering its other end into a suitable capacity 5 - leaking TJ can damage tires and paint on suspension parts, brakes, wheels. On the other hand, the new liquid is guaranteed not to mix with the old one, and part of the fresh TJ that came out during pumping, allowing it to settle to remove air and filtering, can be reused.
- The replaceable TJ is replaced with fresh one, constantly topping it up in the master cylinder reservoir and preventing the system from draining. To do this, each circuit is pumped in turn until fresh fluid appears from the valve.
In this case, air does not enter the hydraulic actuator, but it is possible that part of the old TJ will remain in it, since it is difficult for an inexperienced person to distinguish it from a new one. In addition, more fluid is needed than when pumping in the previous way. Part of it released from the system is mixed with the old and unusable.
- It is necessary to store any liquid only in a hermetically sealed container so that it does not come into contact with air, does not oxidize and does not absorb moisture from it or evaporate.
WARNING
In hydraulic systems, rubber seals based on natural and synthetic rubber are used. The latter can withstand high temperatures well, but such rubber is destroyed by mineral oils, gasoline and kerosene. Therefore, when repairing system components, it is necessary to wash or lubricate the cuffs, and even metal parts, only with fresh, clean brake fluid.
- Brake fluids "Neva", "Tom" and RosDOT are flammable, and "BSK" is flammable. Smoking while working with them is prohibited.
- TJ is poisonous - even 100 cm 3 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.
1 Polyglycols and their esters are a group of chemical compounds based on polyhydric alcohols. They have a high boiling point and good low temperature properties.
2 Silicon-organic polymer products. Their viscosity depends little on temperature, they are inert to various materials, and are efficient in the temperature range from minus 100 to 350°C.
3 SAE - Society of Automotive Engineers (USA), ISO (DIN) - International Organization for Standardization, FM VSS - Safety Measures Act (USA).
4 Silicone-free DOT 5.1 fluids are sometimes referred to as DOT 5.1 NSBBF, and silicone DOT 5 as DOT 5 SBBF. The abbreviation NSBBF stands for "non silicon based brake fluids" and SBBF stands for "silicon based brake fluids".
5 The same must be done when removing air from the system or its circuit. In addition to damage to parts, splashes of pressurized fluid from the valve can enter the eyes.
