One of the important normal use car fluids – brake. About what this fluid is needed for, how often it requires replacement, and which brake fluids to use for optimal performance brake system cars - in our article today.
The role of brake fluid in the “organism” of a car
The brake system, which is responsible for stopping the car in a timely manner and therefore plays important role for the safety of car passengers, it cannot work without brake fluid (BF). She is the one who does main function brake system - transmits through hydraulic drive the force from pressing the brake pedal to the wheel braking mechanisms - pads and discs, as a result of which the car stops. Therefore, even in driving schools, novice motorists are strongly recommended to periodically check the levels of four service fluids: , glass cleaner and brake fluid, on which depends optimal operation cars.
Composition and properties of brake fluids
The basis of the chemical composition of most brake fluids is polyglycol (up to 98%), less often manufacturers use silicone (up to 93%). In brake fluids that have been used on Soviet cars, the base was mineral (castor oil with alcohol in a 1:1 ratio). Use such liquids in modern cars not recommended due to their increased kinetic viscosity (thickens at -20°) and low boiling point (at least 150°).
The remaining percentages in polyglycol and silicone TZ are represented by various additives that improve the characteristics of the brake fluid base and perform a number of useful functions such as protecting the surfaces of the working mechanisms of the brake system or preventing the oxidation of technical components as a result of exposure to high temperatures.
It is not for nothing that we dwelled in detail on the chemical composition of brake fluids used in cars, since many car enthusiasts are interested in the question - “is it possible to mix TK with different chemical bases?” We answer: It is strictly not recommended to mix mineral fluids for the brake system with polyglycol and silicone fluids. From the interaction of the mineral and synthetic bases of these fluids, clots of castor oil can form, which clog the brake system lines, and this is fraught with malfunctions of the brake system. If you mix mineral and polyglycol TZ, then this “hellish mixture” will be absorbed into the surface of the rubber cuffs of the hydraulic brake parts, which will lead to their swelling and loss of sealing.
Polyglycol TK, although they have similar chemical composition, and can be interchangeable, but mixing them in one brake system is still not recommended. The fact is that each technical specification manufacturer can change the composition of additives at its own discretion, and mixing them can lead to a deterioration in the basic performance characteristics working fluid– viscosity, boiling point, hygroscopicity (ability to absorb water) or lubricating properties.
Silicone brake fluids prohibited from mixing with mineral and polyglycolic ones, since as a result the working environment becomes clogged with precipitated chemicals, which will lead to clogging of the brake system lines and failure of the brake cylinder components.
Classification of brake fluids
Today, most countries in the world have uniform standards for brake fluids, known as DOT (named after the agency that developed them - the Department of Transportation - the United States Department of Transportation) - such markings can often be found on packages of brake fluids. It means that the product is manufactured in accordance with the regulatory Federal Motor Vehicle Safety Standards FMVSS No. 116 and can be used in the brake systems of passenger cars and trucks depending on the technical characteristics these vehicles. In addition to the American standard, brake fluids are labeled in accordance with standards adopted in a number of European and Asian countries (ISO 4925, SAE J 1703 and others).
But they all classify brake fluids according to two parameters - their kinematic viscosity and boiling point. The first is responsible for the ability of the working fluid to circulate in the brake system line (hydraulic drive, pipes) at extreme operating temperatures: from -40 to +100 degrees Celsius. The second is for preventing the formation of a vapor lock, which forms at high temperatures and can lead to the brake pedal not working in right moment. When classifying TZ by boiling point, two of its states are distinguished - the boiling point of a liquid without water impurities (“dry” TZ) and the boiling point of a liquid containing up to 3.5% water (“wet” TZ). The “dry” boiling point of the brake fluid is determined by the new, just filled working fluid, which has not had time to “acquire” water and therefore has high performance characteristics. The “moistened” boiling point of TK refers to the working fluid, which has been in use for 2-3 years and contains a certain amount of moisture. Read more about this in the section “Service Life of Brake Fluids”. Depending on these parameters, all brake fluids are divided into four classes.
DOT 3. The “dry” boiling point of this brake fluid is at least 205°, and the “wet” boiling point is at least 140°. Kinematic viscosity such TZ at +100° is no more than 1.5 mm²/s, and at -40 – no less than 1500 mm²/s. The color of this brake fluid is light yellow. Application: intended for use in cars, maximum speed whose movement is no more than 160 km/h, the braking system of which uses disc (on the front axle) and drum (on the front axle) rear axle) brakes.
DOT-3
DOT 4. The “dry” boiling point of this brake fluid is at least 230°, and the “wet” boiling point is at least 155°. The kinematic viscosity of such a TZ at +100° is no more than 1.5 mm²/s, and at -40 – no less than 1800 mm²/s. The color of this brake fluid is yellow. Application: intended for use in vehicles, the maximum speed of which is up to 220 km/h. The braking system of such cars has disc (ventilated) brakes.
DOT 5. The “dry” boiling point of this brake fluid is at least 260°, and the “wet” boiling point is at least 180°. The kinematic viscosity of such a TZ at +100° is no more than 1.5 mm²/s, and at -40 – no less than 900 mm²/s. The color of this brake fluid is dark red. In contrast to the above-mentioned TK, DOT 5 is based on silicone, not polyglycol. Application: intended for use on special vehicles operating in conditions of extreme temperatures for brake systems, and therefore on normal passenger cars not used.
The “dry” boiling point of this brake fluid is at least 270°, and the “wet” boiling point is at least 190°. The kinematic viscosity of such a TZ at +100° is no more than 1.5 mm²/s, and at -40 – no less than 900 mm²/s. The color of this brake fluid is light brown. Application: intended for use in sports brake systems racing cars, in which the temperatures of working fluids reach critical values.
Pros and cons of brake fluids
All of the above brake fluids have their advantages and disadvantages. For convenience, we indicate them in the table below:
| TK class | Advantages | Flaws |
| DOT 3 |
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| DOT 4 |
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| DOT 5 |
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| DOT 5.1 |
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When to change brake fluid?
The service life of brake fluid directly depends on its chemical composition.
Mineral technical specifications due to their chemical characteristics(low hygroscopicity, good lubricating properties) has a fairly long service life (up to 10 years). But when water gets into the liquid, for example, in the event of depressurization of the brake system, its properties change (the boiling point drops, the viscosity increases), and it can no longer perform its functions, which can lead to brake failure. It is recommended to periodically inspect (once a year) the brake system and the condition of the fluid, which can be determined in the laboratory.
Polyglycol TZ has a medium or high degree of hygroscopicity, and therefore its condition should be checked twice a year. You can assess the condition of polyglycol TZ visually: if the liquid has darkened or there are noticeable sediments in it, then you need to check complete replacement. In a year, such a TZ is capable of absorbing up to 3% moisture. If this figure exceeds 8%, then the boiling point of the brake fluid may drop to 100°, which will lead to boiling of the brake fluid and failure of the entire brake system. Automotive manufacturers It is recommended to change polyglycol-based brake fluid every 40 thousand kilometers or every 2-3 years. Typically, such brake fluid is completely changed during the installation of new external brake mechanisms(pads and discs).
Silicone TZ is characterized by long service life, since its chemical composition is more resistant to external influences (moisture). As a rule, silicone brake fluids are replaced after 10-15 years from the moment they were poured into the brake system.
Bicycle brakes different manufacturers may have significant design differences, but one principle unites them unconditionally: brake fluid must be replaced once a year, regardless of how well or poorly the brake system works.
If a cyclist spends a long time in the saddle and rides in areas where frequent, strong or sudden braking is required, then it is possible that the brake fluid will need to be replaced even more often: once every six months.
It is not difficult to visually determine the need to replace the fluid: by placing the brake lever parallel to the ground and unscrewing the cap of the expansion tank, the cyclist can assess whether there are foreign impurities in the brake fluid, whether its color has changed, or whether it has become cloudy. All of the above factors indicate the need for an oil change.
Preliminary preparation for self-replacement
To avoid contamination oily liquid brake pads, it is recommended to remove them from the bicycle before changing the oil. For the same reason, it is advisable to cover the wheels with something.
When choosing brake fluid for your bike, it is important to follow the manufacturer's recommendations. Replace original oil analogues for car brake systems are not worth: car oil may not have the same viscosity parameters and may contain additives that are not suitable for bicycles.
Besides, automotive fluids can corrode rubber seals, which will damage the entire brake system of the bicycle.
Tools for changing brake fluid
Before you start self-replacement bicycle brake fluid, you need to take care of a set of tools. You will need a few of them: a Phillips screwdriver, a No. 7 wrench, a set of hex keys, a container for draining used oil, a piece of plastic tube and a medical syringe (an optional, but very convenient device for pouring oil).
Replacing brake fluid
To drain the waste liquid, you need to put a piece of tube on the valve brake caliper(caliper) and use a wrench to open it, directing the free end of the tube into the drain container.
Pressing the brake lever helps drain the waste fluid. After making sure that the liquid has drained completely, you can proceed to filling hydraulic system fresh oil.
To do this, using a medical syringe or manually, you need to fill expansion tank to the very edges, and press the brake handle several times. The liquid will begin to flow into the hydraulic line, squeezing out air bubbles. As the fluid level in the tank drops, it must be added little by little so that the tank does not remain completely empty.
When the hydraulic line is filled to capacity and excess liquid pours out of the tube into the supplied drain container, the caliper valve can be closed.
The system should not contain air - this is checked by pressing the brake: a soft and sluggish press indicates the presence of air. In this case, the valve must be opened again and the brake fluid must be added, pressing the brake handle until a hard pressing sensation appears.
After tightly closing the brake caliper valve and removing the tube, you need to add fluid to the expansion tank to the very top, after which the tank cap can be screwed on.
Hydraulic brakes are used primarily on those bicycles where high precision, responsiveness and reliability are needed. First of all, these are heavy, massive mountain bikes designed to overcome steep slopes and rises. Hydraulics have also become an integral part of high-speed bicycles, as they allow very precise and accurate as soon as possible Slow.
Principle of operation hydraulic brakes very similar to a mechanical brake, where the brake pads are actuated by a cable. The only difference is that hydraulics use brake fluid instead of cables, and cylinder-piston groups replace levers and eccentrics. Thanks to this approach, the friction forces in the system are significantly reduced, and this increases its service life.
Despite this, hydraulics also have disadvantages, primarily the difficulty of repairing in the event of a breakdown. For example, if there is a breakdown in the hydraulic line, the brakes cannot be repaired in field conditions. The maximum that is possible, if you have the tools, is to bleed the hydraulic brakes.
Hydraulic brake device
Any hydraulic brake consists of at least two cylinders with pistons connected by a line, or more simply put, by a hose that can withstand high pressure. When the cyclist presses the brake handle, the piston forces brake fluid from the master cylinder and transfers it to the slave cylinder located in the car. Here, under the influence of pressure, the pistons begin to extend and put pressure on the brake pads. And due to the friction of the pads on the rotor (brake disc), braking occurs.
Hydraulic system diagram
The cylinders in the brake machine are always used bigger size than in the brake handle. Thanks to this, in accordance with the law of hydraulics, the working brake pistons press on the pads several times more force than a cyclist does when pressing the handle. Also, this law works here due to the fact that two cylinders are installed on the brake machine, or even all 4, 2 on each side.
Symptoms of a Hydraulic Brake Problem
The first sign of a malfunction of such bicycle brakes is that it begins to slow down on its own. This can be explained by air getting into the brake system. This could happen due to the bicycle falling, low level brake fluid in the reservoir, or when the hydraulic circuit opens.
Since air tends to compress, unlike liquids, when it enters the system it acts like a gas spring. That is, the air creates brake fluid pressure, which activates the brakes.
Also, the brake system can engage in similar amateur activities if the working piston jams. The reason for this is water getting into the hydraulic system.
And, of course, the brakes urgently need to be repaired if the brake lever is not as elastic as before, or the hydraulics no longer respond at all to the cyclist’s command to stop the vehicle.
Fault diagnosis and repair
To understand what exactly happened to the braking system of your faithful two-wheeled friend, you first need to do some experiments. The first step is to remove the wheel where this problem appeared. Next, you need to thoroughly clean the brake machine; the easiest way to do this is with a toothbrush. Well, the main goal is to remove the pads.
When access to the working pistons opens, you need to press them in with a screwdriver, and then gently press the brake lever. Both pistons should move forward. If one of them is jammed, you need to use a repair kit to fix the problem. Also piston system you need to carefully inspect for leaks; if they are present, it means the cylinder-piston group is worn out. As a rule, in this case the pistons or special O-rings on them.
Finally, you need to carefully inspect the entire hydraulic line. There should be no kinks, dents or other damage on it. If they are present, the hydraulic line needs to be changed.
Bleeding is the final stage of repair
When the entire system has already been completely rebuilt and assembled, all that remains is to fill in the brake fluid and properly bleed the hydraulics. The system is pumped in order to expel air bubbles from all tubes and cylinders, which prevent the hydraulics from working correctly.
There are many ways to bleed the hydraulic brakes of a bicycle. Anyone can do this at home if they know how to use tools at least a little. Some people use syringes, while others use old and proven methods. Let's consider the simplest and time-tested option.
To bleed the brakes you will need the following components:
- a transparent tube matching the diameter of the bleeder bolt;
- brake fluid or oil, depending on the specific system;
- necessary keys;
- jar or bottle;
- a piece of clean cloth to keep clean.
First you need to put a transparent hose on the bleeder bolt, and lower its other end into a jar that should contain some brake fluid. Next, you need to open the brake fluid reservoir on the handle and make sure that it is on maximum level. If necessary, liquid must be added.
Attention! The brake fluid for each bicycle model is unique and cannot be mixed or replaced.
After this, you can start bleeding the disc brakes on your bike. After pressing the brake handle several times, you need to lock it in the pressed state and at the same time unscrew the bleeder screw on the brake machine. In this case, you can observe how air bubbles come out of the tube. After this, you need to tighten the screw immediately, and only then you can release the handle and pump it again.
This procedure must be done several times until the entire system works as it should. This can be felt by the stiffness of the brake lever.
Video clearly showing the pumping procedure:
And one more way to pump a hydraulic line for the lazy:
Precautions for repairs
When repairing hydraulics on a bicycle, it is unacceptable to get brake fluid on the pads or rotor. If this happens, the elements must be cleaned immediately using fine sandpaper. Otherwise, the brake pads will not work effectively and will quickly fail.
It is also important to know that brake fluid is poisonous and can cause harm to health, so it is not recommended that it come into contact with the skin. Especially avoid contact with eyes.
In addition, it is a good solvent - it easily corrodes the bulk of paint and varnish coatings.
Brakes various manufacturers They are structurally very different from each other, so the recommendations for using brake fluid are also very different.
Before servicing your bike's brakes, be sure to read the manufacturer's instructions!
In particular, the differences relate to the recommended brake fluid. For example, Shimano produces a special mineral oil for its brakes, and only this oil can be used in all models of hydraulic brakes from this company. And Hope recommends using a car brake liquid DOT 4 or DOT 5.1.
Brake fluid is subject to fairly stringent requirements:
- It should not cause corrosion of the metals from which the brake parts are made, and also should not destroy oil seals and seals.
- It should not thicken in the cold.
- It should not expand much when heated (and the disc brake caliper can heat up to very high temperatures during prolonged braking).
- It should not boil when heated (brake failure on long descents is most often associated with heating of the brake parts and subsequent boiling of the brake fluid)
- It must be able to chemically bind water that gets into it (water in the brake hydraulic system not only causes corrosion, but can also boil when the caliper heats up).
Water will still penetrate into the hydraulic system sooner or later, and the brake fluid’s ability to bind this water is limited. Therefore, the brake fluid must be replaced periodically. Usually this does not have to be done often - once every few years.
Replacing brake fluid is described using Shimano 525 brakes as an example.
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Mineral oil SHIMANO has a bright red color, which fades and becomes discolored over time. The brake fluid should be changed when it loses color and turns pale pink. |
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Checking the condition of the brake fluid 1. Loosen the screws securing the brake lever to the steering tube. |
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3. Unscrew the two screws and remove the cap from the expansion tank. |
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Let's see what color the liquid is in the expansion tank. If it’s red (as in the photo), then close the expansion tank and put the brake lever in place. If the liquid in the tank is colorless or has a pale pink color, then it is time to change it. |
Replacing brake fluid
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To replace, you will need, in addition to screwdrivers and keys, a piece of vinyl chloride tube 30-40 cm long (preferably translucent or transparent) and a basin for waste liquid. It is convenient to pour brake fluid into the expansion tank from a medical syringe. To change the brake fluid, it is best to remove the caliper from the bike. In this case, there is no need to worry about brake fluid getting on the disc and pads. In addition, it is easier to bleed the brakes if the hydraulic line is located vertically. Between brake pads you should lay some kind of solid spacer (a piece of cardboard or plastic the same thickness as the brake disc) |
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| Drain the old brake fluid.
1. We put a tube on the valve located on the caliper, and direct the other end of the tube into the basin. 2. Open the valve with the key. |
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3. Press the brake lever several times and watch as the old brake fluid pours out of the tube into the basin. 4. When old fluid stops pouring out, we proceed to filling the hydraulic system. |
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Fill in new brake fluid and bleed the brakes. Let's check that |
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| 1. Pour brake fluid into the expansion tank to the brim. (You can use a medical syringe) 2. Press the brake handle several times. At the same time, air bubbles rise into the expansion tank, and the level of brake fluid in the reservoir decreases - it passes into the hydraulic line. As the fluid level in the reservoir drops, new brake fluid must be added without allowing the reservoir to become completely empty. To make air bubbles rise up to the expansion tank, you can periodically lightly tap the caliper and hydraulic line with your fingers. |  |
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3. At the same time, we look at the tube extending from the caliper. When the hydraulic line and caliper are filled, brake fluid will begin to pour out of this tube into the basin. (The caliper and expansion tank are communicating vessels) 4. Close the valve on the caliper with the key. |
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Let's check that there are no air bubbles left in the hydraulic line.. | ||
Brake fluids
Brake fluid is one of the most important operating fluids in a car, the quality of which determines the reliability of the braking system and safety. Its main function is to transfer energy from the main brake to the wheel cylinders, which press brake linings To brake discs or drums. Brake fluids consist of a base (its share is 93–98%) and various additives, additives, and sometimes dyes (the remaining 7–2%). According to their composition, they are divided into mineral (castor), glycol and silicone.
Mineral (castor)– representing various mixtures castor oil and alcohol, for example butyl (BSK) or amyl alcohol (ASA) have relatively low viscosity-temperature properties, since they solidify at a temperature of -30...-40 degrees and boil at a temperature of +115 degrees.
Such liquids have good lubricating and protective properties, non-hygroscopic, not aggressive to paint and varnish coatings.
But they don't match international standards, have a low boiling point (they cannot be used on machines with disc brakes) and become too viscous already at minus 20°C.
Mineral fluids cannot be mixed with fluids on another basis, as swelling of rubber cuffs, components, hydraulic drives and the formation of castor oil clots is possible.
Glycolic brake fluids consisting of an alcohol-glycol mixture, multifunctional additives and a small amount of water. They have a high boiling point, good viscosity and satisfactory lubricating properties.
The main disadvantage of glycol fluids is hygroscopicity (the tendency to absorb water from the atmosphere). The more water dissolved in the brake fluid, the lower its boiling point, the higher the viscosity at low temperatures, worse lubrication of parts and stronger corrosion of metals.
Domestic brake fluid "Neva" has a boiling point of at least +195 degrees and is colored light yellow.
Hydraulic brake fluids "Tom" and "Rosa" similar in properties and color to "Neva", but have more high temperatures boiling. For Tom liquid, this temperature is +207 degrees, and for Rosa liquid, +260 degrees. Taking into account hygroscopicity at a moisture content of 3.5%, the actual boiling points for these liquids are +151 and +193 degrees, respectively, which exceeds the same indicator (+145) for the Neva liquid.
In Russia there is no single state or industry standard regulating the quality indicators of brake fluids. All domestic producers TZ work according to their own specifications, focusing on the standards adopted in the USA and other countries Western Europe. (SAE standards J1703 (SAE - Society of Automotive Engineers (USA), ISO (DIN) 4925 (ISO (DIN) - International Organization for Standardization and FMVSS No. 116 (FMVSS - US Federal Motor Vehicle Safety Standard).
The most popular at the moment are domestic and imported glycol fluids, classified by boiling point and viscosity in accordance with DOT - Department of Transportation (Department of Transportation, USA) standards.
There is a distinction between the boiling point of a “dry” liquid (containing no water) and a moistened one (with a water content of 3.5%). Viscosity is determined at two temperatures: +100°C and –40°C.
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▪ DOT 3 – for relatively low-speed vehicles with drum brakes or front disc 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 significantly higher.
*It is possible to mix glycol-based brake fluids, but it is not recommended as it may cause deterioration operational properties liquids.
* On vehicles manufactured more than twenty years ago, the cuff rubber may not be compatible with glycol fluids - only mineral brake fluids must be used for them.
Silicone are made on the basis of silicon-organic polymer products. Their viscosity depends little on temperature, they are inert to various materials, are operational in the temperature range from –100 to +350°C and do not adsorb moisture. But their use is limited by insufficient lubricating properties.
Silicone-based fluids are not compatible with others.
DOT 5 silicone fluids should be distinguished from DOT 5.1 polyglycol fluids, as the similarity of names can lead to confusion.
For this purpose, the packaging additionally indicates:
▪ DOT 5 – SBBF (“silicon based brake fluids” - brake fluid based on silicone).
▪ DOT 5.1 – NSBBF (“non silicone based brake fluids” - brake fluid not based on silicone).
DOT 5 fluids are practically not used in conventional vehicles.
In addition to the basic indicators - boiling point and viscosity value, brake fluids must meet other requirements.
Impact on rubber parts. Rubber cuffs are installed between the cylinders and pistons of the hydraulic brake drive. The tightness of these connections increases if, under the influence of brake fluid, the rubber increases in volume (for imported materials, expansion of no more than 10% is allowed). During operation, seals should not swell excessively, shrink, or lose elasticity and strength.
Impact on metals. Hydraulic brake drive units are made of various metals connected to each other, which creates conditions for the development of electrochemical corrosion. To prevent it, corrosion inhibitors are added to brake fluids to protect parts made of steel, cast iron, aluminum, brass and copper.
Lubricating properties. The lubricating properties of brake fluid determine the wear of the working surfaces of brake cylinders, pistons and lip seals.
Thermal stability Brake fluids in the temperature range from minus 40 to plus 100°C must retain their original properties (within certain limits), resist oxidation, delamination, as well as the formation of sediments and deposits.
Hygroscopicity The tendency of polyglycol-based brake fluids to absorb water from environment. The more water is dissolved in the fluid, the lower its boiling point, the fluid boils earlier, thickens more at low temperatures, lubricates parts less well, and the metals in it corrode faster.
On modern cars, due to a number of advantages, glycol brake fluids are mainly used. Unfortunately, over a year they can “absorb” up to 2-3% of moisture and need to be replaced periodically, without waiting until the condition approaches a dangerous limit. The replacement frequency is indicated in the vehicle's operating instructions and usually ranges from 1 to 3 years or 30-40 thousand km.
The properties of brake fluid can only be objectively assessed through laboratory research. In practice, the condition of the brake fluid is assessed visually - by appearance. It should be transparent, homogeneous, without sediment. There are instruments for determining the condition of brake fluid by its boiling point or degree of moisture. Adding fresh brake fluid when bleeding the system after repair work practically does not improve the situation, since a significant part of its volume does not change.
The fluid in the hydraulic system must be completely replaced.
Any brake fluid should be stored only in a hermetically sealed container so that it does not come into contact with air, does not oxidize, does not collect moisture or evaporate; in this case, the fluid is stored for up to 5 years.
