Bleeding the brakes of a car is a simple, but very important and necessary procedure. It can be done with a helper or by one person. To achieve a positive result, it is only necessary to follow a certain procedure for bleeding the brakes. If you act at random or not according to the scheme, you can make it even worse than it was. From this material you will learn: what is the essence of the procedure; in what cases it is necessary; according to what scheme is performed; how to act with a helper and alone.
The essence of the procedure
The brake system of a car is a sealed hydraulic system, the principle of operation of which is based on the property of a fluid not to compress and not decrease in volume with increasing pressure. When the driver presses the pedal, overpressure builds up in the circuits. Brake fluid "presses" on the pistons in the calipers, and they "push" the pads, pressing them against the discs. The pedal begins to resist almost at the very beginning of its stroke and it is impossible to press it to the floor.
The brake system of a car works on the condition that it is sealed and filled only with liquid. Otherwise, the pressure in the circuits cannot increase and the brakes fail. Pressure can be released in different places of the node. Then there is a loss of brake fluid, its volume decreases and pressure is not created.
Brakes cannot work effectively if there is air in the system. Air refers to gases, and even at low pressure they begin to compress and significantly decrease in volume. In the brake system, it is in the form of numerous small bubbles. When you press the pedal, each of these bubbles is compressed, "making room" for the brake fluid. It fills them, which is why the pressure in the circuits does not increase.
The more air, the deeper the pedal "falls through". But most importantly, the brakes become ineffective. If there is too much air, there is a feeling that there are almost none. The car slows down, but it is impossible to stop it quickly. Blame for this air, which is much easier to compress and reduce in volume than liquid.
The essence of pumping the brakes is to remove air from the system. An excess pressure is created in the system, and the brake fluid, together with air bubbles, is squeezed out of all four circuits through the calipers. Fittings are provided in their design for this. The squeezed out, mixture of fluid and air is replenished with fresh brake fluid. The brakes are pumped until liquid without air flows through the caliper fittings, and the pedal begins to normally resist the foot.
When is it necessary to bleed the brakes?
Bleeding the brakes is a mandatory step in any system repair if it has been depressurized. After replacing the pads, when the caliper is not disconnected from its circuit, bleeding may not be required. The same goes for minor repairs and tuning like replacing brackets, painting calipers, turning discs. However, if after that the pedal suddenly “failed”, then it is necessary to bleed the system.
Sometimes the pedal "fails" little by little, suddenly, and without interfering with the brake system. In such cases, pumping is also needed. But you don't have to start with that. If the pedal began to “fail” for no apparent reason, then this is a sign of depressurization of the system and partial loss of brake fluid. First you need to find the problem, fix it, and only then proceed to bleeding the brakes.
Be sure to pump the entire brake system after:
- brake fluid replacement;
- repair of the main brake cylinder;
- replacement of any of the nozzles or hoses of the system;
- caliper repair (piston replacement or repair kit installation).
The first sign that there is air in the system is always a brake pedal that "falls through".
Scheme of pumping car brakes
The brake bleed schedule is a circuit maintenance sequence that varies by configuration. You need to start with the wheel, which is farther from the main brake cylinder than the other three. Since in cars the contours are connected in pairs in the form of the letter “X”, the second wheel is always served, which is opposite the farthest, if viewed diagonally from the body. The third is the remaining back side, and then the corresponding front side.
What is the configuration of the brake circuits on your machine? You can look in the instruction manual, and look for a diagram there. But it's easier to see which side the brake master cylinder is located on. Don't know what he looks like? It is installed in close proximity to the brake fluid expansion tank. This is done so that the brake system has the smallest possible extent and requires a minimum of energy to operate.
For the same reason, the master brake cylinder is located closer to the driver - on the side where the steering wheel and pedal block are. If you have a classic left-hand drive car, then the brake master cylinder is on the left. The wheel farthest from it is the rear right. The longest line goes to it. You have to download it first.
Why is a schema needed? Many people cannot understand this, and pump the brakes randomly. It's faster, more convenient. But wrong. If you do not start with the longest contour, then the result in most cases will not be the best. The pedal may become "hard", but the car will brake badly. To understand why this happens, you need to dive deeper into the structure of the brake system, as well as refresh your knowledge of hydraulics.
We will not do this here. Let's just take it as a rule - you need to pump the brakes according to the scheme:
- The side farthest from the brake master cylinder.
- Front, diagonal.
- Remaining rear.
It is also impossible to make a mistake when, due to laziness (or haste), only one side, the "front" brakes, or the "rear" ones, is pumped. The logic is this: depressurization often happens along one line, and it cannot get into the rest (in theory) air. In practice, this logic often does not work. Half pumped brakes work inefficiently.
Don't rush and don't be lazy! These are the brakes on which the safety of property, health, and life depend. Yours, your passengers, other road users. Always pump the brakes fully. Even if it seems that a “quick” pumping will be enough.
How to bleed the brakes with an assistant
Bleeding the brake system is much easier with an assistant. His role can be performed by a person who has never been behind the wheel. The main requirement is that there should be enough strength and height to press the rather tight pedal to the stop. If you decide to introduce a son of 7...12 years old, then he may not succeed. On some machines, pressing the pedal with sufficient force can be very difficult. If you don't have a strong enough helper, skip ahead to the section on how to bleed the brakes for one person.
To perform the pumping, you will need:
- New brake fluid. recommended by your vehicle manufacturer. You can mix different liquids. But it is better to add what is already in the system. Do not fill the level in the tank with liquid that is squeezed out of the system with air bubbles. At the very least, let it rest.
- Wrench for unscrewing the fitting. There is a possibility that the fittings are rusty. You can't take them with a wrench. Pre-treat all fittings with WD-40 penetrating grease, or make a key with a slot from a box. A socket wrench or ring wrench cannot be used.
- Device for pumping. Pick up the handset. It should be transparent, elastic, and fit snugly over the fluid drain fittings. The second element is a transparent bottle. Volume 0.5...1.5 liters. Plastic or glass.
Unscrew and tighten the fittings for the test so that they do not delay you during work.
The procedure for bleeding the brakes with an assistant:
- Stop the engine.
- Add brake fluid to the expansion tank.
- Prepare the desired side for pumping according to the scheme.
- Connect the fixture to the fitting.
- Give the assistant a signal to download
- Bleed fluid from the system with air.
- Tighten the fitting at the signal of the assistant.
- Check the fluid level in the tank.
- Repeat steps 5-6-7-8.
- Pump over all the remaining contours according to this algorithm.
Start the engine and several times (standing still) press the brake pedal. If it resists almost at the very beginning, then the bleeding of the brake system was successful. Be careful to check the operation of the brakes on the road.
Note! When processing the fittings with penetrating lubricant, it could get on the discs and pads. The first braking can be extremely inefficient. After a few attempts, the parts will dry out, and everything will work. We emphasize that all this must be done carefully, where there are no other road users, there is room “just in case”.
How to bleed the brakes for one person?
Now consider the question of how to pump the brakes yourself if there is no assistant. This can be done in several ways. But they are not equally effective, fast and convenient, and also require different devices. Therefore, consider only the best of the best.
For pumping, excess pressure is created in the expansion tank. Liquid with air bubbles is bled through the fittings on the calipers. The pumping scheme is determined according to the same principle as when working with an assistant.
To create pressure in the expansion tank, you will need either a purchased or home-made device. The simplest can be made in a garage. It consists of four parts:
- A cap that is tightly screwed onto the neck of the expansion tank.
- Fitting for spool nipple.
- Car camera.
Attach one end of the hose to the cap, and fasten the fitting on the other. Inflate the chamber with a pump or compressor.
How to bleed the brakes alone:
- Add brake fluid to the reservoir.
- Put on the cap with hose and fitting.
- Prepare the desired circuit for pumping - remove the wheel, connect a tube with a bottle to bleed the fluid with air.
- Connect the inflated chamber to the device on the tank - the pressure in the system will increase.
- Bleed liquid with air bubbles through the fitting.
- Continue until clear, air-free fluid flows from the caliper.
- Repeat the procedure for all circuits according to the scheme.
You can create pressure in the expansion tank in other ways. For example, a large syringe with brake fluid, hermetically attached to the spare cap. Recall that for this method of pumping, you can buy a ready-made device in a car shop.
Video: car brake bleeder
Do not forget! After bleeding the brakes, always carefully check their performance.