Replacing the brake fluid on a car with abs. Brake Fluid Replacement

24.09.2019

Salon

Reading 6 min. Views 1.6k. Posted on October 30, 2015

In this article we will tell you how to properly bleed the brakes with ABS.

Signs you need to bleed your ABS brakes

Air also enters the anti-lock braking system. Since the circuit of such a brake system is hydraulic, air significantly impairs its performance. Determining the accumulation of air in the circuit of the brake system is quite easy. If the kickback of the brake pedal becomes softer when pressed, it means that air has appeared in the brake system.

Air can enter the ABS brake system in the following cases:

— When repairing the hydraulic drive of the brake system;

- When replacing a caliper on one of the wheel hubs;

— In case of a long idle time of the car;

- In the case of ongoing repairs of various components of the vehicle's brake system;

- When replacing the entire volume of brake fluid in the circuit.

A modern anti-lock braking system consists of the following main components:

- hydraulic accumulator,

Good day, dear motorists! Among us, most likely, there is no driver who at least once did not experience a feeling of helplessness at the moment of braking. When the car continues its movement, and not at all in the direction in which the driver wants. Skid.

Fortunately, engineering thought does not stand still. The modern driver is armed with a system such as ABS. Let's take a closer look at the system and see if it is possible to bleed the brakes with ABS with your own hands.

What is car ABS

ABS (Anti-lock Braking System) is an anti-lock braking system that prevents the wheels from locking during emergency braking.

The main task of the ABS is to regulate the speed of rotation of all wheels. This is done by changing the pressure in the vehicle's brake system. The process occurs with the help of signals (impulses) from each wheel sensor, which enter the ABS control unit.

The principle of operation of the anti-lock braking system
The contact patch of the wheels of the car is in relative immobility to the roadway. According to physics, the wheels are affected by the so-called. static friction force.

Taking into account the fact that the static friction force is greater than the sliding friction force, with the help of ABS, the rotation of the wheels is effectively slowed down at a speed that corresponds to the speed of the car at the time of braking.

At the moment of the beginning of braking, the anti-lock braking system begins to constantly and accurately determine the speed of rotation of each wheel, and synchronizes it.

Anti-lock system device
Here are the main components of ABS:

sensors installed on the wheel hubs of the car: speed, acceleration or deceleration;
control valves installed in the line of the main brake system. They are also components of the pressure modulator;
ABS electronic control unit. Its task is to receive a signal from sensors and control the operation of valves.

Bleeding brakes with ABS, taking into account the features of the system

Bleeding the ABS brake system will require you to have certain technical skills. In addition, it will not be superfluous to study the manual for the installation and maintenance of the brake system of your car.

Features of pumping brakes with ABS

in cars that have in one node: a hydraulic valve block, a hydraulic accumulator and a pump, changing the brake fluid and bleeding the brake system with an anti-lock braking system is done in the same way, you need to turn off the system by removing the fuse. Bleeding of the circuits is carried out with the brake pedal depressed, the RTC bleeder must be unscrewed. The ignition is turned on and the pump expels air from the circuit. The bleeder screw is tightened and the brake pedal is released. An extinguished malfunction lamp is evidence of the correctness of your actions.
Bleeding of the brake system with ABS, in which the hydraulic module with valves and the hydraulic accumulator are separated into separate units, is carried out using a diagnostic scanner to read information from the ABS computer. You probably don't have it. Therefore, bleeding brakes with ABS of this type, most likely, should be done by you at the service station.
Bleeding the brake system with ABS and with electronic activation systems (ESP or SBC) is carried out only under service conditions.

How to bleed ABS brakes

It is important! It should be remembered that the pressure in the brake system reaches 180 atm. Therefore, in order to prevent the release of brake fluid, before disconnecting the brake lines for any system with ABS, it is necessary to discharge the pressure accumulator. To do this, with the ignition off, press the brake pedal 20 times.

Technology of pumping the brake system with ABS

Bleeding brakes with ABS, like bleeding a conventional brake system, is performed with an assistant. Turn off the ignition (position "0"). Disconnect the connectors on the brake fluid reservoir.

Front wheel brakes:

put the hose on the bleeder fitting;
open the fitting for a turn;
the brake pedal is pressed to the stop and held in the depressed position;
we observe the exit of the "airy" mixture;
turn the screw on and release the pedal.

Rear right wheel brake:

put the hose on the bleeder fitting, unscrew it one turn;
press the brake pedal to the stop, turn the ignition key to position "2". In this case, the brake pedal is held in the depressed position;
a running pump will force air out of the system. That is, as soon as the brake fluid begins to come out without air bubbles, close the fitting and release the brake.

Rear left wheel brake

the hose is put on the fitting and unscrew it 1 turn;
DO NOT press the brake pedal;
a working pump pushes out the “airy” mixture;
press the brake pedal halfway and tighten the fitting;
release the pedal and wait for the pump to stop completely.

In the reverse order: turn the ignition key to "0", connect the connectors to the brake fluid reservoir, carry out a leak test of the brake system (see ABS fault indicator).

Good luck with bleeding your ABS brakes.

At the factory, the entire brake system is completely empty, but its design is such that the fluid reservoir is located on the master brake cylinder in the engine compartment, at the very top. A little lower is usually the ABS unit (who has it), and then the brake pipes go to the front and rear wheels. There, in wheel brake mechanisms, cylinders of different versions can be used. But one feature unites all of them: at the very top of the cylinder there is always a bleeder. It is also sometimes referred to as an air release valve.

Elements of the working brake system of a car with ABS: 1 - front wheel brake mechanism; 2 - tube brake mechanism of the front wheel; 3 - ABS block; 4 - hydraulic drive tank; 5 - main brake cylinder; 6 - vacuum amplifier; 7 - brake pedal; 8 - tube of the brake mechanism of the rear wheel; 9 - rear wheel brake cylinder; 10 - rear wheel brake hose; 11 - front wheel brake hose

At the factory, a special fitting is put on the neck of the tank, through which brake fluid fills the system under pressure. The worker, located below, opens the bleed fittings on the wheel cylinders in turn. Air is forced out of them first, and then brake fluid comes. All. The fitting can be turned. By repeating this operation with all the wheels of the car, we get a fully charged and efficient brake system. It remains to disconnect the filling fitting from the neck of the reservoir mounted on the main brake cylinder, and wrap the cap of the reservoir.

The question arises, can an ordinary car owner use the same method? If you've been repairing a brake system with hydraulic components replaced, or are bleeding the system because you suspect it has air in it, I usually recommend a classic pump-and-hold bleed. More intensive passage of fluid in the tubes and cavities of the cylinders is guaranteed to displace air bubbles.

Don't try this at home?

But what if we were going to, in accordance with the maintenance schedule for our car, just change the fluid? Someone every two years, someone - every three. And here the method of pouring the system with new brake fluid comes to the rescue. We use the fact that the liquid tank is located high, and the liquid simply drains down to the working cylinders under the influence of gravity. The main advantage of the proposed method is that it does not require an assistant.

Brake fluid should be purchased with a margin (at least 1 liter). It is interesting, by the way, that almost all cars, regardless of their size, cross-country ability, availability of systems and other differences, have a brake system capacity of about half a liter. Please note that the replacement takes place by mixing, so you need to spill a slightly larger amount of liquid through the system. Stock up on 1 liter of brake fluid from any manufacturer (they are all compatible). DOT-4 is the most common brake fluid used in the vast majority of vehicles. It has to be replaced due to its high hygroscopicity - the ability to absorb moisture from the air and lose its performance because of this.

So, an independent replacement of the brake fluid will require you to install the car on an inspection ditch or overpass and provide a free passage between the place where you can replenish the brake fluid reservoir in the engine compartment and the brake cylinders of all four wheels.

We work in stages

We pump out the brake fluid from the tank with a rubber bulb or syringe. Add new fluid to the top edge. To speed up the process (in order to release liquid from all cylinders at once), it is advisable to pick up four pieces of tubes that fit tightly on the bleed fittings of all cylinders. We lower the free ends of the tubes into transparent bottles of a small capacity.

We turn off the fittings of all brake cylinders. We make sure that the liquid has flowed through all four tubes. We control the decrease in fluid from the tank located on the brake cylinder, and immediately replenish the tank. We observe an increase in the level of liquid in bottles located near the wheel brake cylinders.

It is necessary several times to change the role of the observer for draining the fluid from the fittings of the brake cylinders to the role of the controller, replenishing the fluid level in the reservoir on the brake cylinder in order to prevent it from draining.

The fastest filling, as a rule, occurs in the case of a bottle into which a hose is lowered, coming from the brake cylinder of the front left wheel. As soon as there is about 200 ml of liquid in the bottle of the front left wheel, we wrap and tighten the fitting of the local cylinder. Repeat the same with the front right wheel. We complete the process on the rear axle - here 200–250 ml of liquid must pass through each fitting.

That's it, the brake fluid change is complete. It remains only to make sure that all fittings are tight. We put on protective caps, specify the fluid level in the reservoir of the main brake cylinder - and go.

How to change the brake fluid in a car with ABS?

The procedure for replacing brake fluid (TF) on cars with an anti-lock braking system (ABS) of different designs is different, so it is better to entrust the work to the service station masters (preferably branded). To replace the brake fluid, experts use equipment that pumps TJ into the system under pressure. This reduces the risk of “airing” the brake system and the ABS unit.

It is permissible to replace it yourself only as a last resort, if you have certain technical skills, and only on cars with ABS 1980 - 90 onwards, following the instructions for servicing this car.

In cars with ABS, in which the pump, hydraulic accumulator and hydraulic valve block are located in the same unit, the fluid in the brake lines is replaced in the same way as in a conventional car without ABS (see "AC" No. 11 "2006). To do this, it is enough to first switch off the system by removing the appropriate fuse.

To fill the ABS unit with fluid when replacing it, the ABS power is restored and the ignition is turned on. At the same time, the accumulator pump starts to work. As soon as the unit is full (the sound of the pump should change from a high tone to a low one), the ignition must be turned off (the pump without a “brake” can operate for no more than 2 minutes).

After replacing the TJ, it is necessary to bleed (bleed) the brake lines and the ABS unit itself. The pumping of the first is carried out, as in a conventional car. Pumping circuits connected to the pump has its own characteristics. It is performed with the brake pedal depressed and the bleeder valve of the working cylinder turned away. When the ignition is turned on, the pump expels the “airy” liquid from the circuit through the fitting. Then the fitting is twisted and the pedal is released. If the TJ replacement is done correctly, after sealing the brake lines, the “ABS Fault” light on the instrument panel will go out.

In a car with ABS, where the pump with a hydraulic accumulator and the hydraulic module with a valve system are made as separate units, the algorithm for replacing the TJ and bleeding the system is somewhat different. In the hydraulic module, the sequence of opening its valves is important, therefore, these operations can only be carried out using a diagnostic scanner that allows you to remove information from the ABS computer (such equipment is usually not available to motorists).

It is even more difficult to replace the TJ on cars with electronic security systems that activate the brakes (for example, ESP and / or SBC) - in this case, the procedure is carried out using a special technology specified by the automaker. For its implementation, special equipment (including computer equipment) is required, which is available only at branded service stations.

It should be remembered that before disconnecting the brake lines of vehicles with ABS of any design, it is necessary to discharge the pressure accumulator by pressing the brake pedal at least 20 times with the ignition off. Without this, liquid can be ejected (the system maintains a pressure of about 180 atm). For the same reason, care is needed when turning on the ignition with a depressurized hydraulic system - in this case, the accumulator pump will start working.

Prepared by Yuri Datsyk, Alexander Landar, Vladimir Kornitsky
Photo from the editorial archive

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How to change the brake liquid on vehicles with anti-lock braking system?

Into the floor The units of the anti-lock braking system in the form of a hydraulic unit are integrated into the standard brake circuit. In addition to them, wheel speed sensors are installed and By analyzing the wheel speed, the system maintains the best pressure in the circuit, preventing it from blocking.

Analysis of types of existing systems

At 1st glance replacement brake water with Abs is an obvious procedure. But the modern auto industry forces us to reckon with safety trends: in fact, in all cars, the anti-lock circuit is combined with the EBD brake force distribution system and the ASC traction control method. In general, these nodes are often controlled by ESP - the exchange rate stability system.

With similar high-tech packages, the function should only be carried out by authorized service centers. The reason is the need to connect a diagnostic scanner to the computer. For the same reason, it is unrealistic to carry out a replacement on cars without the help of others, where the pump with a hydraulic accumulator and the valve system are made as separate assembly units.

Servicing the system on your own can only be done on a car with such an assembly: a hydraulic accumulator and a valve block are connected in one unit.

Preparing to replace the brake fluid of a car with ABS: conditions and necessary tools

In the process of servicing the deceleration system of a car, open access to the working cylinders of each wheel is needed. Therefore, a more suitable place for work is a viewing ditch or overpass.

When performing the procedure, an assistant and a set of devices are useful:

a set of open-end wrenches;
a honey syringe of huge volume and a hose corresponding to the diameter of the tip, about 10-15 cm long (candidate - pear);
containers for extracted brake water;
tube 20-30 cm long; diameter - slightly less than the diameter of the fitting on the brake cylinders (to ensure tightness).

Technology for changing brake fluid on vehicles with a combined hydraulic accumulator and valve block

The operation of changing the brake water in the system with Abs is carried out in several steps:

draining the existing composition from the tank;
pumping highways;
pumping the Abs module.

The task of draining the working fluid from the expansion tank located in the engine compartment is solved as follows:

pump out liquid from the tank with a syringe;
fill in the new composition to the highest mark (MAX, High);
close the container.

bay and disconnecting the power blocks on the tank cover, you should proceed to pumping the hydraulic system. The traditional purge cycle looks like this:

Replacement brake fluid on their own

In this issue of the "Technical Environment", its presenter Gennady Emelkin will talk about how to change without the help of others.

How to bleed brakes with ABS Audi A4, A6, Passat B5

How to upgrade brakes With ABS You can contribute materially to the channel.

unscrew the fitting with an open-end wrench by 1 turn;

3-5 times to push the brake pedal and hold down (does a partner);

after the end of the water flow screw the fitting and release the pedal.

the aspect of stopping the repetition of the cycle is the absence of air bubbles and a visually clean liquid, indicating the removal of an old working fluid;
since in the system under consideration the rear brake line is under the highest pressure, only the front brakes can be pumped by the traditional method (first left, then right).

The bleeding of the rear circuits connected to the ABS equipment is carried out together with the bleeding of the anti-blocking module. Acts with the right rear cylinder:

connect the drain hose and open the fitting;
press the brake pedal;
turn on the ignition;
after the exit of air bubbles has stopped and a new composition has appeared, close the fitting;
release the pedal;
turn off the ignition.

Alternative solution to the issue

vakuumnik The presence of a drain fitting in the design of the anti-lock module may be discussed in the owner's manual of a car with ABS. To service a similar system, a compressor or a home-made installation in the form of a pear and a converted brake water reservoir cap may be useful. The development of a substitution in this case looks much simpler:

remove the used liquid from the container and fill in the new one;
bleed all four brake cylinders in the traditional way according to the scheme discussed by the manufacturer;
install a special adapter for a compressor or a home-made installation instead of the “brake reservoir” cover;
connect a hose to the drain fitting of the anti-blocking module and unscrew it by 1 turn;
make the pressure about 1 BAR;
identify the end of the exit of old water and bubbles;
release pressure.

In the process of replacing the used brake water with the latest in the system with Abs, the following points should be taken into account:

you need constant control over the water level in the tank: lowering below the low mark (MIN, Low) is not allowed;
admissible operating time of the hydraulic pump - 2 minutes, in case of exceeding - turn off the ignition and let it cool down for 5-10 minutes.
before draining the water, you need to “discharge” the system by pressing the brake pedal more than 20 times;
it is strictly forbidden to pour the used liquid or the composition that has stood in an open container for a long time;
when the ignition is turned on and the drain fitting is open, you should be prepared for a sharp release of water.

Summary

Read also

Without the help of others, it is possible to change the water only on cars with a hydraulic accumulator and valves combined into one unit. List of required equipment:

syringe with extension tube or pear;
transparent container;
transparent tube 20-30 cm long;
open-end wrenches on "8" or "10".

Briefly about the procedure brake replacement water in a car with Abs on its own:

change the composition in the newest tank;
bleed the left and right front brake cylinders;
pump the rear right cylinder with the brake pedal depressed and the pump turned on;
bleed the rear left cylinder with the brake pedal released and the hydraulic pump turned on;
check the system for tightness.

If there is a drain fitting on the ABS module, you should bleed all 4 brake cylinders according to the scheme discussed by the factory in the traditional way, and then “drive out” the ABS unit with excess pressure supplied from the outside.