Brake fluid is a very important component of any car. From the name it is clear that it is poured into the brake system and directly contributes to braking, that is, the system works on the hydraulic principle. But pour into the system, do not understand that it is impossible! There are many reasons for this; special compounds with certain properties are used here. Today I want to tell you - what they consist of and why they definitely need to be changed ...
By the way, I received such questions on my blog - “Tell me, is it possible to fill ordinary water into the brake system? And that will be?" It can be seen a young inquisitive mind, as they say - comprehends the world! Read on and you'll understand.
A few words about the brake system
I just want to remind you how it works. In any car there is a brake pedal, if you "roughly exaggerate" it is connected with the brake working cylinder. After you press this pedal, pressure is created in the brake system, it presses on special pistons in the brake calipers (or rear cylinders) that compress (in the case of front-wheel drive) or spread (in the case of rear-wheel drive) brake pads. And already they, in turn, squeeze the brake disc or stop the drum from the inside, I advise you to read -.
I think everyone knows the principle of operation of this system, in our article it is necessary for the next understanding of the material.
System warm-up
When braking, the discs or drums get very hot. Actually, this is a law of physics, friction occurs - brake pads rub against a metal surface, there is a large release of heat. The pads are made of a special “thermo” and “wear-resistant” material, so they can walk for a very long time, this material does not heat up as much as compared to discs or drums.
But their heating can be simply catastrophic (especially near the front axle) there are a lot of videos on the Internet where they heat up to “red”.
And what happens - parts of the brake system, namely pistons, cylinders, and experience huge temperature loads. At high speeds, temperatures can reach up to 150 degrees Celsius. Do you understand what I mean? Actually now we will start talking about the compositions.
What can and cannot be uploaded
Now I want to answer the reader - let's take a look at ordinary water. Why is it STRICTLY IMPOSSIBLE to FILL. YES, actually, everything is simple - even if you don’t dig deep, water boils and evaporates at high temperatures, and at low temperatures it freezes already at -1 degree. You come in this winter, start the car, but there are no brakes! The system is frozen! Also imagine - the system boils when braking, steam pours out of the system tank, the efficiency is at zero. However, even if freezing and boiling are hypothetically defeated, then water has ONE BIG DEFECT - it oxidizes and provokes rust, after a short period of time, the pistons in the calipers will simply rust, the seals that are designed to walk on a smooth and clean surface will break and water will flow out.
Alcohols (in pure form) are also not suitable, because they boil, and even ignite.
Transmission oils, motor oils - oils may be suitable, but again, not all.
They have really low evaporation, they also resist high temperatures very well (especially motor ones), but at low temperatures they can thicken (this negatively affects fluidity), and they can also negatively affect the rubber of the oil seals! That is, calipers or cylinders can leak.
Different formulations of brake fluid
So what did we understand - that the brake fluid must have high fluidity, lubricate, protect against corrosion, not freeze, withstand temperatures in the range of 150 - 170 degrees Celsius, not boil! THAT is such - "super liquid".
Probably, I won’t surprise anyone by saying that “brakes” are still evolving - WELL, NOW THERE IS NO IDEAL COMPOSITION WHICH WOULD 100% MEETING ALL REQUIREMENTS.
Mineral compositions - it all started with them, I will say that they were used on old cars that did not even have front disc brakes, only drums. YES, and speeds at that time rarely exceeded 60 km / h.
Their composition has long been known - castor oil with the addition of butyl or ethyl alcohol, this is a kind of base, but many manufacturers mixed other minerals and petroleum products of various degrees of purification into the composition. It is difficult to call such a composition ideal, but there are still positive points:
- They lubricate well.
- They practically do not absorb moisture, that is, if we say “scientifically”, they have low hygroscopicity
However, there are more cons:
- At temperatures of 110 - 130 degrees boil
- At -20 degrees they begin to thicken
- In addition, castor oil adversely affects parts made of brass, aluminum, copper
- Also, for a long time they could not find a formula that, over time, would not decompose rubber products - oil seals, cuffs, etc.
For a very long time they fought over the formula with castor oil, added all kinds of additives and other substances, but its time has already passed.
Glycol brake fluids - are now used quite widely, you can know under the abbreviations (DOT3, DOT4, DOT 5.1). They contain polyethylene glycols and polyesters of boric acid, comply with all international standards, and have also passed the Russian GOST certification.
This composition is almost perfect, boils at + 150, + 200 degrees, perfectly lubricates, protects against rust, is almost neutral to rubber elements.
The minus here is one and quite large - high hygroscopicity, they absorb moisture very strongly, so it is MANDATORY to change it every 2-3 years! Otherwise, the calipers begin to turn sour and rust.
Silicone brake fluids (DOT5 and special version DOT-5.1/ABS). The composition here is completely different from the counterparts, based on organosilicon polymers. There are enough pluses - it does not absorb moisture, it is absolutely neutral to rubber and metals, it is always fluid (it does not depend on temperature).
There are also disadvantages, and where without them - the lubricating properties are at a low level, so there is more wear on the seals (when compared with counterparts). Such compositions are rarely used on production versions of cars; as a rule, they are poured into sports or racing cars, where the heating of the calipers is much higher.
In the proposed article, we will tell you why a car is so important, what properties it has and when it needs to be replaced.
Brake fluid actuates the hydraulic drive. Namely, pressure is transferred from the main brake cylinder, which obeys the brake pedal, to the wheel brake cylinders. The latter, thanks to the brake pads, slow down the movement. Now imagine what the consequences could be if this whole process does not take place efficiently, and the car stops moving later than necessary?
Brake Fluid Requirements:
- firstly, it must perform its functions at any temperature: be it minus 30 or plus 150 (the temperature in the brake cylinders at the time of intense braking);
- secondly, it must react well with both metals and rubber sealing parts of the hydraulic system;
- thirdly, the brake fluid must have high lubricating properties. This condition is very important for brake cylinders, namely for their internal surfaces;
- fourthly, the properties of the brake fluid should not depend on the operating conditions.
Based on the above requirements, it is created, which includes 92-98% of the base and special additives.
Types of brake fluid.
Depending on what is included in the basis, there are such types of brake fluid:
Mineral. It has low cost, high lubricating properties. Its aggressiveness to rubber is very low. Main disadvantages:
- at temperatures below minus 20 it is quite viscous;
- boiling point is quite low.
Used this type of brake fluid only in older cars because it is neutral to rubber seals.
Glycolic. It contains ethers and polyglycols. This base is very popular due to its high performance properties. Increased hygroscopicity is its main disadvantage.
Silicone. The most modern and completely non-hygroscopic. It is used very rarely because:
- incompatible with other types of bases;
- poorly compatible with rubber parts;
- has increased requirements for the quality of pumping;
- pretty expensive.
The main properties of the brake fluid.
Boiling temperature. When a liquid boils, vapor is released, which is compressed. This process leads to the fact that the pedal "fails" and there is no braking. Often such a problem is observed when they often slow down. It is in this situation that the heat from friction is not removed in time from the brake system, and the overall temperature increases.
Viscosity at various temperatures. Critical cases: thickening at low temperatures or increased fluidity at high temperatures.
How often is the brake fluid changed?
Experts recommend making brake fluid replacement every two to three years. Because due to the difference in operating temperatures, the brake fluid easily absorbs moisture from the air and even when condensed. This ability results in low lubrication in the warm season and thickening in the cold season. And the most terrible thing is that it is enough to dissolve only 3% of water in the brake fluid in order to reduce the boiling point by 70 degrees. This fact is the main reason for the replacement.
Change brake fluid you can do it earlier if you find impurities, or notice that the transparency has decreased. However, it is quite difficult to objectively assess the state of the liquid, because it does not mix in the system. Consequently, different properties of the brake fluid are observed in the reservoir and in the working cylinders.
What brake fluid should be filled in?
The most important condition is to follow the manufacturer's requirements, since the braking system is designed for certain parameters. brake fluid. Do not forget that quite often the manual prescribes how often it needs to be replaced.
To mix brake fluid or not to mix?
Mixing is strictly prohibited. brake fluids different classes! Since there is a possibility of additive incompatibility, it is also not advised to mix fluids from different manufacturers, even if they are within the same class. Use only the brake fluid specified by the manufacturer.
How to add "brake" correctly?
Everything is very simple here, the main thing is to remember which one was previously filled in the car. Buy the same and add to the brake reservoir. Be sure to keep it at the "max" mark. As practice shows, with a working brake system, it has to be topped up once a year.
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 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.
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.
In brake systems with a hydraulic drive, the following brake fluids are mainly used: BSK, Neva, Tom, Rosa - in domestic cars, SAE J 1703ISO 4925, DOTZ, DOT4, BOT4 +, DOT5.1, DOT5, Racing Formula DOT 6 - in foreign cars.
Basic properties of brake fluid
1.BOILING POINT
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 effectiveness of the brake system is reduced.
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.
