Hydraulic brakes on a bicycle provide the predicted response rate, absolute accuracy, and they are much more powerful mechanical, therefore are installed mainly for the extreme and high-speed type of riding.
The mechanism of action of hydraulics is similar to mechanical: brakes begin to work as a result of tension of cables, but in hydraulic system Instead of cables, brake fluid works, and the lever and eccentric are replaced by the cylindrophone group.
Therefore, hydraulic brakes are much easier to slow down, because when braking less effort is spent than in mechanical.
But, unlike the mechanics, hydraulic brakes It is much more difficult to repair, with a test of hydrolynas, the repair of the system in hiking conditions is impossible, the only thing that can be taken without professional equipment- pump the brake system.
About what bicycle brakes are, you can read.
Structure of hydraulics
The hydraulic brake consists of a "tank" with a liquid on the brake handle, the hydrolynya and caliper, consisting of a cylinder and piston.
The braking reaction begins as a result of pressing the brake lever, which leads to a movement of the piston, and in turn it squeezes the liquid from the main reservoir and directs it to the hydraulic line to the workspace.
In the cylinder under the pressure of the liquid, the piston movements come in the movement and affect the blocks, the braking occurs as a result of friction.
Cylindrical mechanism B. brake machine always larger in size than in the control lever, so pressure on brake pads It is performed in a reinforced amount, much greater than the pressure on the lever.
Bicycles, scooters, components
Also, the load is enhanced by setting several brake cylinders.
Breakdown mechanism
The main sign of the hydraulic breakdown is "falling out" brake handle when braking.
This is due to the appearance of air bubbles in the hydraulic system, due to the fall, lowering the level of fluid or the rupture of the connected circuit inside the hydraulics.
The air is compressed when the air is compressed, creates pressure, leads to the movement of the pistons and starts the mechanism.
To clarify the cause of the failure, it is necessary to eliminate the usual contamination, and the pads are removed for this, the brake machine is cleaned.
After that, the pistons are pressed by specialness: it is pressed on the brake lever to the full extension of both pistons, if they are jammed - the cylindrical system is worn, in this case the pistons and special sealing rings are changing, oil is replaced in the system.
Also, independent triggering of the brakes can occur as a result of jamming the brake piston after water from entering.
Hydraulics must be repaired even with minor failures.
In addition to mechanical damage to the shell, 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, the efficiency of the system is reduced.
Air penetration is also possible due to the expansion of the tank, this happens if you pull the lever on the inverted bike.
For renewal normal work must be spent maintenance Hydraulic brakes on a bicycle: completely pump hydraulic system.
Through hydraulics
The hydraulic fluid differs from different manufacturers.
In the hydraulic system of bicycles, the company Shimanu, Tektru, Maguru - Mineral or semi-synthetic oilsAll other firms use dot brake fluid.
It should also be borne in mind that in AVIT and Formulu hydraulics there are no connecting tubes for pumping, so the syringe kit with a sleeve M5 / 0.8 will be needed.
The main difference between liquids: the brake fluid dot is hygroscopic, that is, over time, it absorbs moisture and can lose its properties, it should be changed every 2 years, regardless of the mileage, but oil does not absorb moisture, but over time it darkens, and if all the water It will fall into the fluid, then when mixed, it becomes "whites".
In addition, mineral oils are chemically not aggressive and does not harm the plastic or paint and varnish bike coating.
Methods of service
There are two ways to maintain hydraulic bike brakes:
Direct pumping
With direct pumping hydraulic oil, the oil is poured directly in expansion tank And after clamping the lever heads down the hydraulic system.
In the process of work, it is necessary to constantly trace the oil level indicator and pour a new portion of the liquid to prevent the tank emptying, while tapping the key or screwdriver over the tank and hydrolynium to drive out the air from the system.
During the passage of fluid, the hose overlaps, after that he drops several times to the limit of the lever and the valve opens. Under the influence of pressure, the air passes into the pipe, holds the brake lever and the valve overlaps.
In the expansion tank, the fluid is hung and it continues until the oil of a homogeneous consistency and without air bubbles appears.
At the end of the operation, brake fluid is added, and the tank closes.
Reverse pumping
- 200 ml syringe is introduced through a short tube on the caliper valve;
- The lever overlaps and air from the caliper and the hydraulic cord is absorbed;
- Caliper's valve overlaps, the hose with a syringe is disconnected, air bubbles are squeezed;
- The syringe is inserted into place and the procedures are repeated until the air purification of hydraulics is completely cleansing;
- The next step is to complete the hydraulic system of the brake fluid.
This method is convenient to pump fluid in brakes, if you cannot squeeze all air from the system with direct pumping. And pumping in the first way requires more time.
Also, in this way the air is reaping from the opposite half of the caliper without its own valve.
Detailed video equipment for maintenance of hydraulic brakes:
Why to choose brake fluid Need to relate as serious as possible? The fact is that the uninterrupted operation of the brake system and, accordingly, the safety of the car largely depends on it. When the driver presses the pedal, the brake fluid, which is in the pressure system, transmits an effort to the piston of the caliper, and the piston on the pads. The brakes are triggered, and the car stops. But due to the resulting friction, fluid heating occurs. If it boils, it will lose its important property - incompressible. In this case, the system will almost cease to respond to the press of pedals and stop will be very, very difficult, since the force of the brake pads is not transmitted.
Basic properties of brake fluid
Brake fluids have a number of characteristics, from which their operational qualities directly depend. It:
- hygroscopic;
- frozen temperature;
- aggressiveness.
From the level of hygroscopicity, the ability of the liquid to absorb moisture. The lower this indicator, the better. This is due to the fact that the moisture, falling into the brake fluid, worsens its properties, in particular, lowers the booster temperature.
The aggressiveness of the brake fluid determines the extent to which it has a negative impact on the gaskets and other elements of the system made of rubber or plastic.
Frozen temperature - Extremely important parameter. In severe frost, the brake fluid can become extremely thick, it ceases to circulate in the system. In this case, the driver is difficult to press the brake pedal, and it may have serious problems With driving safety. In Russia, which is famous for the whole world with its cold winter, it is necessary to use the 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 that is developed by the US Department of Transport (USDOT). According to it, all products related to this category are divided into several classes, from DOT-1 to DOT-5. The most important thing you need to know about them:
- dOT-1 and DOT-2 fluids are practically not used today;
- DOT-3 - Glycol-based brake fluid, relatively aggressive with respect to paint coatings and rubber products with a high level of hygroscopicity, with a booster point of 205 degrees Celsius (provided moisture in it);
- DOT-4 - This category includes brake fluids on a glycal basis that corrupt paint, but do not have a negative impact on rubber products; They have less hygroscopic compared to DOT-3 products and boil at 230 degrees Celsius (provided that they did not absorb water);
- DOT-5 is a more modern variety of brake fluid, in which silicone with a package of additives is used as the basis, so that it practically does not absorb water, safe for paint coatings and rubber parts, boils at 250 degrees Celsius;
- DOT-5.1 is a brake fluid on a glycol-based basis with a relatively high level of hygroscopicity, aggressive with respect to paint coatings, but safe for rubber parts, boiling at 275 degrees Celsius (provided that it did not absorb water).
Inside each category there may be products with improved characteristics, although the official classification does not provide them. For example, in addition to the DOT-4 brake fluid, you can find DOT-4.5 and DOT-4 Super. Also, each type, except 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 relating to different classes, as a rule, have different colour. This allows the driver to visually determine, with which product it deals, avoid mistakes or random mixing:
- DOT-3, DOT-4, DOT1 - Yellow (from light yellow to light brown);
- Dot-5 - red or pink color.
Since the brake fluids DOT-3, DOT-4 and DOT-5.1 are manufactured on a glycal basis, they can, in principle, can be mixed. but different manufacturers can use different additive packages; Therefore, according to experts, combined products created by one manufacturer. For example, you can mix brake fluid Liqui Moly. With other similar products of the same company. Accordingly, DOT-5 products made on silicone basis are not compatible with DOT-3, DOT-4 and DOT-5.1.
The most versatile and accessible in terms of cost today is the brake fluid DOT-3. Most often it is used in passenger and trucks Early releases that are not exploited too intensively.
DOT-4 - universal, but somewhat more expensive product. It suits almost for any car with disk brakes, and thanks to 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 fairly expensive product that is well suited for vehicles with low mileage and cars that are operated in conditions of increased and even extreme humidity.
When choosing a brake fluid, you must be guided by the following parameters:
- recommendations of the manufacturer's company;
- mileage, status of the brake system,
- type, mass, power characteristics of your vehicle.
Beginner cyclists who do not understand all the intricacies of the work of the bicycle and care for it, probably faced with questions on the operation of the brake system. A handle was sold, new blocks are badly slowed down when changing the brake fluid - we will try to answer our article to the main questions.
Running in new brakes
All new disc brakes, brakes after overhaul, or partial replacement of components need running time. In this case, it does not matter - mechanical or hydraulic. During the period of running, the efficiency of the brakes is reduced, so jumping "from the room in the quarry" and use the brakes to the entire coil is not desirable. Special attention You should turn to new brakes when the brake disc is not tied at the same time, and the pads. Do not forget about running and when replacing brake pads - in this case The duration of the runoff is reduced.
During the running period occurs 2 important moments. First - smooth surface New brake pads should be rough. Second - The brake pad material should get into the surface of the brake disc. Due to the running, the brake work improves - braking becomes more smooth, the efficiency of the entire system increases, vibration disappears and foreign sounds.
When running brakes, you can make a set of events:
- Make 3-4 stops slightly stronger than normal braking. It will warm up the rotors so that when the running does not happen the temperature blow.
- Make 8-10 strong braking without stopping, for example, from 35 km / h to 5 km / h.
- In the process of braking, you can feel that the brakes have become "wadded" - this is the norm, because They have greatly heated. After braking, ride 5-10 minutes so that the rotors can cool from the incident air flow.
Mineral oil or dot?
In hydraulic disc brakes, a special braking fluid is used to transmit efforts from the brake knob to brake pistons. In the process of the evolution of bicycle brake systems, manufacturers came to two standards "TORROSUCHU" - DOT and mineral oil.
- DOT (US DEPARTMENT OF Transportation) - became the common name of the working brake fluid in vehicles (not only in bicycles). Key feature of dot'a is a high boiling point of the liquid. At the same time, the boiling point decreases when dot begins to absorb water, so ideally change dot every 12-18 months.
- Mineral oil - produced from oil and is a mixture of hydrocarbons separated from gasoline. It is used in different industries (including cosmetology), including used as brake fluid. Liquid compression levels and boiling point are approximately similar to dot.
All other things being equal, the boiling point of mineral oil and dot is approximately the same, but "mineral water" has one an important nuance - She does not absorb moisture, but accumulates it in the hydraulic system. If the accumulated water reduces the efficiency of the brakes, then in the "mineral unit" at high temperatures of the brakes the water evaporates and leads to the failure of the system failure. Similarly, the brakes on the "mineral milk" are not recommended to be used in the cold season, since the water accumulated in the system during freezing is expanding and the gums of the pistons in a caliper or the brake knob may simply be simply squeezed. Treaty and starting to slow down, it can be found that there are no brakes, so when using the bicycle year-round use, it is recommended to use a brakes onto dot or change to mechanical analogs.
Another very important nuance - brake fluids Not interchangeable! Systems designed to work on "mineral milk" will not work on dot and vice versa. Such systems like Avid / Sram, Formula, Hayes and Hope Use dot 4 or 5.1. Systems Magura, Shimano.and Tektro. Use "mineral water".
Brake pads - organic or metal?
Organic brake pads are made from a mixture of fibers and connecting them resin. Due to the softer structure, it is believed that they are much quieter of their metal analogues. However, silence has back side Medals - they quickly overheat and with long-term braking begin to lose their properties. In addition, in conditions of dampness, their wear is significantly increased, there were examples when the pads were fully rated with a short trip to the rain.
Metallized pads have much greater reliability, because In their composition, metal fibers compressable at high temperatures. They are better tolerant dirt and dampness, they are not so wear out when moisture gets into key difference From the organic matter is that they do not lose their properties and retain efficiency with long-term braking. The main minus is noise when working and overheated by hydraulic fluid.
I still brake perfectly, is it necessary to serve?
It is the opinion that the maintenance of brakes includes only timely replacement Pad. As we found out above, the replacements require not only the pads, but also the brake fluid, preferably - once a year or two, depending on the intensity of use.
The first plan comes out of air and fluid in the brake system. Over time, the brake handle begins to fall to the infraces, the braking efficiency is reduced and the brake pumping is required. As the brakes can be used service maintenance Handles and Caliper - either full busting system or a bulkhead with partial replacement Rubber and seals.
Four brake care councils:
- Try not to pollute the brake system. Be careful with the lubricant chain - it is desirable not to use a spray smear and a chain cleaner in the form of a spray, since the oil or cleaning agents on a fatty-based basis are out of construction. When you wash a bicycle, try not to knock down the dirt from the bike and chains towards the rotor.
- Remove the rotor cleaning agent for brakes. Special means On the basis of the solvent, pollution and oil particles are removed from pads and rotors, which increases the efficiency of brakes.
- Check the tightening of the bolts or fastening the center-lock rotors. With a poorly tightening, the rotor begins to "walk", causing vibrations and reducing the efficiency of the brakes, which can lead to an accident.
- Inspection hydrolynes and mechanisms for the presence of leaks. Wear no one excluded - it is quite likely that with the time of the gum can be crying, come into disrepair and the hydraulic fluid will flow. Early diagnosis allows you to solve the problem with the smallest losses, while riding with a flow can fail the pistons and other details.
Hydraulic brakes are used primarily on those bicycles where high accuracy, reaction speed and reliability are needed. First of all, it is heavy, massive mountain bikes designed to overcome steep slopes and lifts. Also, the hydraulics has become an integral part of high-speed bicycles, as it allows it very accurately and in as soon as possible Slow.
The principle of operation of hydraulic brakes is very similar to mechanical, where the brake pads are driven by a cable. The difference is only that in hydraulics instead of cables, the brake fluid is used, and the levers and eccentrics replace the cylindropional groups. Thanks to this approach, friction force in the system is significantly reduced, and this increases its service life.
Despite this, the hydraulics also has the disadvantages, first of all it is difficulty in repair during breakage. For example, when the brake hydraulic highway test does not come out in the field. Maximum, which is possible in the presence of tools, it is pumping hydraulic brakes.
Device hydraulic brakes
Any hydraulic brake consists of at least two cylinders with pistons connected by a highway, or simply speaking, a hose withstanding high pressure. When a cyclist presses the brake knob, the piston displaces the brake fluid from the main cylinder and transmits it to the working cylinder, located in a typewriter. Here, under the influence of pressure, the pistons begin to extend and press on the brake pads. And already due to the friction of the blocks about the rotor (brake disc) and braking comes.
Diagram of the hydraulic system
The cylinders in the brake type are always used greater than in the brake handle. Thanks to this, in accordance with the law of hydraulics, working brake pistons are put on the pads several times with more power than the cyclist makes it pressing on the handle. It also works this law due to the fact that two cylinders are installed on the brake type, and then all 4, 2 on each side.
Signs of hydraulic brake malfunction
The first sign of the malfunction of such bicycle brakes is that it independently starts to slow down. This can be explained by the fact that air hit the brake system. This could happen due to the fall of the bike, low level Brake fluid in a tank, or when operating a hydraulic chain.
Since the air has the property to shrink, unlike liquids, it is triggered as a gas spring when entering the system. That is, the air creates the pressure of the brake fluid, which activates the brakes.
Also, the brake system can be engaged in similar amateur in case, in the case of a crossing of the working piston. And the cause of this is the fall in the hydraulics system.
Well, of course, the brakes urgently need to be repaired if the brake handle has not become such an elastic, as before, or the hydraulics is already not reacting at all to the cyclist command to stop transport.
Diagnostics of faults and repair
To understand what exactly happened to brake system Your faithful two-wheeled friend, you need to first do some experiments. First of all, you need to remove the wheel where this problem appeared. Next, you need to clean the brake machine, it is easier to do this with a toothbrush. Well, the main goal is to remove the pads.
When access to the working pistons appears, you need to press them with a screwdriver, and then smoothly click on the brake handle. Both pistons must be advanced. If one of them jammed, you need to apply Repair Kit to eliminate the fault. Also piston system It is necessary to carefully examine on the subject of the flow, if they are present, it means that the cylindropional group is worn. As a rule, in this case there are pistons or special sealing rings on them.
In conclusion, you need to carefully inspect the entire hydraulic line. It should not be beggars, dents and other damage. If they are present, hydrolynia must be changed.
Pumping - Final Stage Repair
When the whole system has already been completely moved and assembled, it remains only to pour the brake fluid and properly pump the hydraulics. Pouring the system in order to drive out of all tubes and cylinders air bubbles that interfere with the hydraulics work correctly.
Ways, how to pump hydraulic bike brakes, there is plenty. Make it can each at home, if at least a little knows how to handle the tools. Someone applies syringes, and someone uses old and proven ways. Consider the easiest and time-tested option.
For pumping brakes, you will need such components:
- transparent tube suitable for the diameter to the bolt of pumping;
- brake fluid or oil, depending on the specific system;
- the necessary keys;
- bank or bottle;
- a piece of clean fabric to maintain purity.
At first, you need to wear a transparent hose to the bolt for pumping, and the other end of its end to the jar, where there should be a little brake fluid. Next, you need to open a tank with brake fluid on the handle and make sure that it is at the maximum level. If necessary, liquid needs to be addressed.
Attention! The brake fluid for each model of the bike is unique and they cannot be mixed or replaced.
After that, you can start pumping disc brakes by bike. By pressing the brake knob several times, you need to fix it down and at the same time unscrew the screw for pumping on the brake type. At the same time, it is possible to move like air bubbles will go from the tube. After that, the screw must be spinning immediately, and only then you can go to the handle and download again.
This procedure must be done several times until the entire system is working as it is necessary. This can be felt on the stiffness of the brake lever.
Video, clearly showing the pumping procedure:
And one more way to pump hydrolynes for lazy:
Precautions for repair
When repairing hydraulics on a bike is unacceptable to hit the brake fluid on the pads or rotor. If this happened, the items must be cleaned immediately with shallow sandpaper. Otherwise, the brake pads will not work effectively and quickly fail.
It is also important to know that the brake fluid is poisonous and can harm the health, so it is not recommended that it falls on the skin. Especially need to avoid eye entrances.
In addition, it is a good solvent - easily eats the bulk of paintwork.
