bicycle brakes different manufacturers may have significant design differences, but one principle unites them unconditionally: the replacement of the brake fluid must be carried out once a year, regardless of how well or poorly the braking system works.
If a cyclist spends a lot of time in the saddle and rides in areas where frequent, strong or sharp braking is required, then it is possible that the replacement of the brake fluid will be required even more often: once every six months.
Visually determining the need to replace the fluid is not difficult: by setting the brake lever parallel to the ground and unscrewing the cap of the expansion tank, the cyclist can assess whether there are impurities in the brake fluid, whether its color has changed, whether it has become cloudy. All of the above factors indicate the need for an oil change.
Preliminary preparation for self-replacement
To avoid pollution oily liquid brake pads, it is recommended to remove them from the bike before changing the oil. For the same reason, it is desirable to cover the wheels with something.
Choosing liquid for brake system your bike, it is important to follow the manufacturer's recommendations. Replace original oil analogues for car brake systems are not worth it: automotive oil may not match the viscosity parameters, contain additives that are not suitable for bicycles.
Besides, automotive fluids can corrode rubber seals which will damage the entire brake system of the bike.
Tools for changing brake fluid
Before proceeding to 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 tubing and a medical syringe (optional, but a very convenient device for filling oil).
Brake Fluid Replacement
To drain the waste liquid, it is necessary to put a piece of pipe 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 used 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 out expansion tank to the very edges, and press the brake lever several times. The liquid will begin to go into the hydraulic line, squeezing out air bubbles. As the level of liquid in the tank decreases, 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 will pour 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: soft and sluggish pressing indicates the presence of air. In this case, the valve must be opened again and the brake fluid must be added by pressing the brake handle until a hard pressure is felt.
Tightly closing the brake caliper valve, and removing the tube, you need to add liquid to the expansion tank to the very top, after which the tank cap can be screwed on.
brakes- this is one of essential elements bike. They can be mechanical - this is when a cable is used to transfer energy from the handle to the braking mechanism, as well as hydraulic, in this version brake fluid. ()
Basically, each manufacturer recommends its own hydraulic brake fluids, produces special mineral oil and does not recommend using anything else. Hope recommends using an automotive brake DOT liquid 4 or DOT 5.1.
Liquids are subject to high requirements:
1) The liquid should not cause corrosion of metals, as well as destroy oil seals and seals;
2) Fluids must be resistant to low temperatures, should not thicken and freeze;
3) It should also be resistant to high temperatures, should not expand and boil when heated;
4) Must be able to chemically bind the water that enters it (water in the hydraulic brake system not only causes corrosion, but can also boil when the caliper is heated).
Some of the existing brake fluids:
There are two fundamental different types liquids that are poured into the brakes are mineral oils (Magura, Shimano) and DOT3 / 4/5 brake fluid (Haes, Hope, Formula).
Since these liquids have different bases, they should never be mixed or replaced. Brake fluid has a more aggressive effect on metals and seals, therefore, in brakes designed for mineral oil, “brake fluid” cannot be filled in!
Automotive brake fluids.
1. DOT3- glycol base
boiling point - + 205C
<1500
viscosity stability at +100С — >1.5
ultra-high hygroscopicity, service life - 10-12 months
2. DOT4- glycol base
boiling point - + 230C (actually - about 260)
viscosity stability at -40С —<1800
viscosity stability at +100С — >1.5
high hygroscopicity, service life - 24 months
3. DOT5- silicone base
boiling point - + 260C (actually - up to 300)
viscosity stability at -40С —<900
viscosity stability at +100С — >1.5
almost zero hygroscopicity, high lubricating properties, while the complete absence of anti-corrosion properties; service life - up to 15 years
4. DOT5.1- glycol base
boiling point - + 250C (actually - about 280)
viscosity stability at -40С —<900
viscosity stability at +100С — >1.5
highest fluidity, low hygroscopicity, service life - up to 5 years
slurry properties are provided by synthetic additives
mineral oils for hydraulic brakes:
1. Branded oils Shimano and Magura.
2.Motorex Hydraulic Fluid 75
3. Citroen Hydraulic.
4. Any mineral oil from an auto shop with the least amount of any additives.
One of the important for normal operation car fluids - brake. About why this fluid is needed, how often it needs to be replaced, and which brake fluids to use for optimal operation of the brake system of the car - in our today's article.
The role of brake fluid in the "organism" of the car
The braking system responsible for the timely stop of the car and therefore playing important role for the safety of the passengers of the car, it cannot work without brake fluid (TK). It is she who performs main function brake system - transmits through hydraulic drive the force from pressing the brake pedal to the brake mechanisms of the wheels - pads and discs, as a result of which the car stops. Therefore, even in driving schools, novice motorists are strongly advised to periodically check the levels of four service fluids: , glass cleaner and brake fluid, on which the 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 used on Soviet cars, the base was mineral (castor oil with alcohol in a ratio of 1: 1). Use these liquids for modern cars not recommended due to their increased kinetic viscosity (thickens at -20°C) and low boiling point (at least 150°C).
The remaining percentages in polyglycol and silicone TK are represented by various additives that improve the characteristics of the brake fluid base and perform a number of useful features such as protecting the surfaces of the working mechanisms of the brake system or preventing the oxidation of TK as a result of exposure to high temperatures.
It was not in vain that we dwelled in detail on the chemical composition of brake fluids used in cars, since many motorists are interested in the question - “is it possible to mix TK with different chemical bases?”. We answer: mineral liquids for the brake system, it is strongly not recommended to mix with polyglycol and silicone. From the interaction of the mineral and synthetic bases of these fluids, castor oil clots can form, which clog the lines of the brake system, and this is fraught with malfunctions of the brake system. If you mix mineral and polyglycol TK, 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 a similar chemical composition, and can be interchanged with and, but mixing them in one brake system is still not recommended. The fact is that each manufacturer of technical specifications can change the composition of additives at its discretion, and mixing them can lead to a deterioration in the main performance characteristics. working fluid- viscosity, boiling point, hygroscopicity (ability to absorb water) or lubricating properties.
Silicone brake fluids it is forbidden to mix with mineral and polyglycol, since as a result the working environment is clogged with precipitated chemicals, which will lead to clogging of the brake lines and failure of the brake cylinder units.
Classification of brake fluids
Today, in most countries of the world, there are uniform standards for brake fluids, known as DOT (after the name of the department that developed them - the Department of Transportation - the United States Department of Transportation) - this marking can often be found on brake fluid packages. It means that the product is manufactured in accordance with FMVSS No. trucks depending on the specifications these vehicles. In addition to the American standard, brake fluids are labeled in accordance with the 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 line of the brake system (hydraulic drive, tubes) at extreme operating temperatures: from -40 to +100 degrees Celsius. The second - for preventing the formation of a steam "plug", which is formed during high temperatures and may cause the brake pedal to not operate in right moment. When classifying HP by boiling point, two of its states are distinguished - the boiling point of a liquid without water impurities (“dry” HP) and the boiling point of a liquid containing up to 3.5% water (“wetted” HP). The "dry" boiling point of the brake fluid is determined by the new, freshly filled working fluid, which did not have time to "collect" water and therefore has high operational characteristics. The “moistened” boiling point of TK refers to a working fluid that has been in operation for 2-3 years and contains a certain amount of moisture in its composition. Read more about this in the Brake Fluid Lifespan section. 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 “moist” one is at least 140 °. Kinematic viscosity such TK at +100° - no more than 1.5 mm² / s, and at -40 - at least 1500 mm² / s. The color of this brake fluid is light yellow. Application: designed for use in cars, maximum speed movement of which is not more than 160 km / h, in the brake system of which disc (on the front axle) and drum (on rear axle) brakes.
DOT-3
DOT 4. The "dry" boiling point of this brake fluid is at least 230°, and the "wetted" one is at least 155°. The kinematic viscosity of such a TK at +100° is no more than 1.5 mm² / s, and at -40 - at least 1800 mm² / s. The color of this brake fluid is yellow. Application: Designed for use in vehicles, the maximum speed of which is up to 220 km / h. In the braking system of such cars, disc (ventilated) brakes are installed.
DOT 5. The “dry” boiling point of this brake fluid is at least 260 °, and the “wetted” one is at least 180 °. The kinematic viscosity of such a TZ at +100° is no more than 1.5 mm² / s, and at -40 - at least 900 mm² / s. The color of this brake fluid is dark red. Unlike the technical specifications mentioned above, DOT 5 is based on silicone, not polyglycol. Application: designed for use on special vehicles operating in conditions of extreme temperatures for brake systems, and therefore on normal cars not used.
The "dry" boiling point of this brake fluid is at least 270°, and the "wetted" 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 - at least 900 mm² / s. The color of this brake fluid is light brown. Application: intended for use in braking systems of sports 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 list them in the table below:
| TK class | Advantages | Flaws |
| DOT 3 |
|
|
| DOT 4 |
|
|
| DOT 5 |
|
|
| DOT 5.1 |
|
|
When to change brake fluid?
The life of the brake fluid directly depends on its chemical composition.
Mineral TK by virtue of its chemical characteristics(low hygroscopicity, good lubricating properties) has a fairly long service life (up to 10 years). But when water enters the liquid, for example, in the event of depressurization of the brake system, its properties change (the boiling point drops, the viscosity rises), and it can no longer perform its functions, which can lead to brake failure. Periodic inspection (once a year) of the brake system and the condition of the fluid, which can be determined in the laboratory, is recommended.
Polyglycol TK has a medium or high degree of hygroscopicity, and therefore its condition should be checked twice a year. It is possible to assess the condition of polyglycol TK visually: if the liquid has darkened or precipitation is noticeable in it, then it is necessary to conduct it complete replacement. In a year, such a TZ is able to absorb up to 3% moisture. If this indicator exceeds 8%, then the boiling point of the brake fluid may drop to 100 °, which will lead to boiling of the fuel oil and failure of the entire brake system. Automotive manufacturers It is recommended to change the brake fluid based on polyglycols every 40 thousand kilometers or every 2-3 years. Usually such a brake fluid is completely changed during the installation of new external brake mechanisms(pads and discs).
Silicone TK is distinguished by its durability of operation, since its chemical composition is more resistant to external influences (moisture ingress). As a rule, the replacement of silicone brake fluids is carried out after 10-15 years from the date of filling into the brake system.
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Today I will tell you how to bleed the Shimano Deor 615 hydraulic brake, which is installed on the Merida Kalahari bike, without a special kit. Everything that will be described below will work for any other Szyman brakes!
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Choosing mineral oil for hydraulic brakes
The most important thing we need to bleed the brakes is mineral oil and the necessary tool.
Note that there are two types of hydraulic brakes, one using mineral oil and the other DOT-4. These fluids are not compatible. If you mix them up, you'll ruin your brakes and you'll have to throw them away. Be careful!
Brake manufacturer Shimano recommends buying their special mineral oil for servicing. This oil now in stores it costs 1200-1300 rubles per liter. But you can save money and buy mineral water as good as Shimano. This oil is called "LHM +" and costs around 400 rubles per liter. Agree, the difference in price is 3 times! Most bike shops and cyclists use it.
Liter can of Febi Bilstein mineral oil 06162 When I went to the store for LHM+, it was out of stock. The seller offered to buy an analogue - mineral oil Febi Bilstein 06162 (for power steering) for 600 rubles. I decided to take it. At home I have already read on various forums that Febi oil is also great for bicycle hydraulics and even slightly outperforms LHM +.
With tools, as well as with oil, you can also save decently. Shimano offers to buy a special funnel (Shimano SM-DISC Oil Stopper) for bleeding the brakes, which costs from 250 to 350 rubles. You will also need a small bottle of oil and a tube (SM-DB-OIL), which are connected to the brake caliper and cost about 500 rubles.
Shimano brake bleeder and tube
All these original instruments can be replaced with 3 syringes of 20 cubes (even two can be used) and a dropper from any pharmacy and meet less than 100 rubles.
- The first syringe will be filled with mineral oil and will be connected via a dropper to the caliper.
- The second syringe will be stuck into the hole on the brake lever where the funnel is installed (pictured above). The syringe will be used without a plunger.
- The third syringe is needed in order to pump out excess oil from the second syringe so as not to stain the bike.
Preparatory work before pumping
- When bleeding the system, it is necessary to protect the brake discs and pads from oil as much as possible. If it gets on the discs, they can be degreased, and the pads will most likely have to be thrown away. Therefore, they should be covered with rags or removed from the bike during this procedure. In order not to stain the discs, it is enough to remove the wheels, and the pads will need to be pulled out of the brake calipers.
I usually set wheel from another bike, which does not have brake disc, this allows you to work comfortably without a special stand and there is no danger of contaminating the disc.
Don't press the brake lever after the pads have been removed, otherwise the pistons will have to be bred! To prevent this from happening, you need to use the plastic plugs that usually come with new brakes. I didn't have these plugs with me when I bled, so I used a wheel mount and a small rag to keep the mount tight.
If suddenly you still pressed the brake and brought the pistons together, separate them using a pry bar or something safe (plastic), since pistons can be ceramic and a screwdriver can crack.
- Before you start bleeding the brakes, you need to loosen the clamp of the brake lever of the brake that you will pump and install it parallel to the ground, then (in point 2) you will understand why this was necessary.
Shimano Brake Bleeding Process
1. We collect brake fluid in the first syringe. We cut off a small piece from the dropper and connect it to the syringe. We fill the tube with mineral oil and attach it to the fitting on the brake caliper. (Try to avoid air bubbles in the syringe and tubing)
Syringe with mineral oil before connecting to the brake calliper. I then squeezed out the air at the tip of the tube, filling it with oil. 2. Next, use the second syringe, which is inserted into the pen. We remove the piston from it. It is necessary to take the tip with the needle and remove (cut off) the needle (I did it with pliers). This tip must be put on the syringe and screwed in instead of the cork, the plastic from the needle should be tightly screwed into the threaded hole and not leak. Next, we need to pour some oil into this syringe.
I start screwing the syringe into the brake lever. The syringe should wrap well along the thread and sit tight. 
This is what happened after screwing in the syringe. 3. Now we need to unscrew the inlet nipple on the brake machine so that the liquid from the first syringe goes into the hydraulic system. We press on the piston and drive the liquid through the hydraulic line into the syringe at the top.
The photo shows the border between Szyman's oil (red) and my Febi oil (green). This means that there is a new mineral water in the entire hydraulic line. 
I recommend securing the syringe with a tie in the position shown in the photo so that the air that is in the system comes out to the top and does not get back into the hydraulic line when the piston is pressed. We press until a little oil remains in the first syringe - this means that you have definitely squeezed out all the air from the system.
Since I got a full syringe of mineral oil, I still have 1/3 left. We twist the inlet nipple to which the dropper was connected, and remove the syringe in place.
4. In this step, we need to make sure that there are no bubbles left in the system. We begin to actively press on the handle and see if air comes out of our syringe installed in the brake lever. I also recommend taking a hexagon and changing the position of the handle (put it a little higher and work with the brake, then a little lower and work with the brake). After making sure that no more bubbles come out, you can proceed to step 5.
5. Now insert the plunger into the second syringe and carefully unscrew it from the handle (this is necessary in order not to spill everything on the bike and the floor). Next, at a fast pace, we twist the cork and put the brake lever in a comfortable position.
Congratulations! Your brakes are pumped! It remains now to test them in combat conditions! Good luck!
Video with the process of bleeding Shimano brakes using a special tool:
Shimano brakes that can be bled this way: Acera M395, Alivio M4050, M355, M365, M315, M396, MT500, M596, M6000, M425, M445, M447, M505, M506, M575, Saint M820, SLX M675, SLX M7000, XT M8000, XT T785, XTR M9000, XTR M9020, XTR M985, XTR M987, XTR M988, ZEE M640.
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Hydraulic brakes on a bike provide predictable responsiveness, absolute precision, and they are much more powerful than mechanical brakes, so they are mainly installed for extreme and high-speed riding.
The mechanism of action of hydraulics is similar to mechanical: the brakes begin to work as a result of the tension of the cables, but in the hydraulic system brake fluid works instead of cables, and the lever and eccentric are replaced by a cylinder-piston group.
Therefore, hydraulic brakes are much easier to brake, because less effort is expended during braking than mechanical ones.
But, unlike mechanics, hydraulic brakes are much more difficult to repair; if a hydraulic line breaks down, it is impossible to repair the system in field conditions, the only thing that can be done without professional equipment is to bleed the brake system.
You can read about what bicycle brakes are.
The structure of hydraulics
A hydraulic brake consists of a "tank" with fluid on the brake lever, the hydraulic line itself and a caliper consisting of a cylinder and a piston.
The brake reaction is initiated by pressing the brake lever, which drives the piston, which in turn squeezes the fluid out of the main reservoir and directs it through the hydraulic line to the work area.
In the cylinder, under the pressure of the fluid, the pistons move and act on the pads, as a result of friction, braking occurs.
Cylindrical mechanism in brake machine always larger than in the control lever, so the pressure on brake pads produced in a reinforced size, much higher than the pressure on the lever.
Bicycles, scooters, components
Also, the load is increased when installing several brake cylinders.
mechanism breakdown
The main symptom of a hydraulic failure is the "failure" of the brake lever during braking.
This is due to the appearance of air bubbles in the hydraulic system, due to a drop, a drop in the liquid level, or a break in the connected circuit inside the hydraulics.
When air enters, it compresses, creates pressure, sets the pistons in motion and starts the mechanism.
To find out the cause of the failure, it is necessary to exclude ordinary pollution, for this the pads are removed, the brake machine is cleaned.
After that, the pistons are pressed in with a special tool: the brake lever is pressed until both pistons are fully extended, if they are jammed, the cylindrical system is worn out, in this case the pistons and special O-rings, the oil in the system is changed.
Also, independent operation of the brakes can occur as a result of jamming of the brake piston after water has entered.
Hydraulics need to be repaired even with minor failures.
Except mechanical damage shells, over time, brake fluid or hydraulic oil changes its consistency and begins to absorb air and moisture through microscopic gaps.
As a result, the fluid changes its color, the brake lever fails, and the efficiency of the system decreases.
Air infiltration is also possible due to the expansion of the tank, this happens when you pull the lever on an upside down bike.
To resume normal operation, you must Maintenance hydraulic brakes on a bicycle: bleed the hydraulic system completely.
Hydraulic purge
Hydraulic fluid varies from manufacturer to manufacturer.
In the hydraulic system of Shimanu, Tektru, Maguru bicycles - mineral or semi-synthetic oils, all other firms use DOT brake fluid.
It should also be taken into account that Avit and Formulu hydraulics do not have connecting pipes for pumping, so you will need a syringe kit with an M5 / 0.8 sleeve.
The main difference between liquids: DOT brake fluid is hygroscopic, i.e. over time it absorbs moisture and may lose its properties, it should be changed every 2 years, regardless of mileage, oils do not absorb moisture, but over time it darkens, and if water will get in into a liquid, then when mixed it becomes "whitish".
In addition, mineral oils are not chemically aggressive and do not harm plastics or paintwork bike.
Maintenance methods
There are two ways to maintain a bicycle's hydraulic brakes:
Direct pumping
With direct bleeding of the hydraulic system, oil is poured directly into the expansion tank and, after clamping the lever, is directed down the hydraulic system.
During operation, it is necessary to constantly monitor the oil level indicator and add a new portion of liquid to prevent the tank from emptying, while tapping the tank and hydraulic lines with a wrench or screwdriver to expel air from the system.
During the passage of the liquid, the hose is blocked, after which the lever is lowered to the limit several times and the valve opens. Under the influence of pressure, air passes into the pipe, the brake lever is held and the valve is closed.
Liquid is poured into the expansion tank and this continues until an oil of a homogeneous consistency and without air bubbles appears.
At the end of the operation, brake fluid is added and the tank is closed.
Reverse pumping
- A 200 ml syringe is inserted through a short tube onto the caliper valve;
- The lever is closed and air is sucked in from the caliper and hydraulic cord;
- The caliper valve is closed, the hose with the syringe is disconnected, air bubbles are squeezed out;
- The syringe is inserted into place and the procedure is repeated until the hydraulics are completely free of air;
- The next step is to completely fill the hydraulic system with brake fluid.
In this way, it is convenient to pump fluid into the brakes if it is not possible to squeeze all the air out of the system during direct bleeding. And pumping the first way requires more time.
Also, in this way air is pumped out of the opposite half of the caliper without its own valve.
Detailed video guide for hydraulic brake maintenance:
