If the brake pedal moves "softer" (fail), and its working stroke has increased, then there is air in the system. This affects braking performance. Bleeding the brakes is a must. Otherwise, the creation of emergency situations is guaranteed.
Bleeding the brake system is also required after any, even minor, repair (if there was an intervention in it). Each specialist has his own "keys" and "chips." We will cover the basics. Pumping the brakes will require the participation of an assistant.
The actions described below cannot be performed on vehicles equipped with ABS (auto-locking system), since other, special tools are needed to pump the brake system of these vehicles. In this case, it is better to entrust the work to specialists.
There are several types of brake systems. There are diagonal, there are parallel. Pumping of brakes begins from the farthest highway so that there is no air left in the system.
Parallel pumping system: rear right and rear left, then front right, then front left. In the diagonal, the pumping of the brakes takes place in a slightly different way: rear right, front left and rear left, front right (since they are in separate contours of the brake master cylinder). If you have a fluid leak on one of the circuits, then the second circuit will help stop the car. In this case, the braking efficiency will drop significantly, however, when the alarms are turned on, you can get to the nearest service station, eliminate the malfunction and pump the brakes.
The first one. In the event that air enters the system due to a drop in the liquid level in the feed tank or when the brake pipes are separated from the main cylinder, brake units must be pumped (all four).
The second one . When the brake tube is separated only at the wheel, then it is necessary to pump only this caliper or the brake working cylinder.
The third. If the brake pipe is separated somewhere between the main cylinder and one of the brakes, the part of the system serviced by the disconnected pipe should be pumped.
Well, now - the course of work, the purpose of which is to dump the residual air (brake booster unit) by repeatedly pressing the brake pedal. The engine, of course, must be turned off.
Remove the cap from the tank of the master cylinder and fill it with brake fluid. Replace the cover. Do not save on liquids! Buy only high quality!
We are preparing a vessel (transparent, clean), a piece of tube (made of plastic or rubber), suitable for the pumping fitting in diameter (it must be tightly tightened), brake fluid, wrench.
We start with the rear right wheel. We slightly loosen the bleeder valve and clamp it in a position that will allow it to quickly loosen.
We connect one end to the bleeder fitting (we fit it), the second - we immerse it in a prepared transparent container with brake fluid.
Now the assistant enters the work. He should press the brake pedal slowly several times to create pressure in the system and hold the pedal in the lower position.
Now open the pumping nozzle and wait for the beginning of the fluid outlet. You need to monitor the air bubbles coming out of the tube, immersed in a container. When the fluid flow slows down in this tube, we hold the fitting in and ask the assistant to release the pedal.
We repeat the manipulations until the brake fluid flows clean, without air. Then we clamp the fitting and go alternately to the front left wheel, to the left rear and to the front right. The procedure is repeated every time. Constantly check the fluid level in the master cylinder tank.
At the end, fill the tank of the main cylinder with liquid. Check the operation of the brakes. If there are failures, the pumping of the brakes is repeated. The pedal must be resilient.
Important: brake fluid is not reused!