Turns fall when you press the brake: possible causes, solutions and recommendations

A car is a multifunctional system where the coordinated and synchronized operation of all mechanisms and each node is important. Various malfunctions and breakdowns of at least one of the details may lead to violations of a clear algorithm for the operation of other systems. It is not uncommon to encounter a situation where the revolutions fall when the brake is pressed. With this trouble often turn to auto mechanics. If during the braking suddenly started to swim the speed, do not wait until the car gets up. Soon after this, the engine will begin to vibrate strongly and stall. By the way, the problem is actual only on gasoline engines.

Possible reason

Turns fall when the brake is pressed due to various malfunctions in the vacuum brake booster. To find out the reason more precisely, it is necessary to know how the given node is arranged. Knowing how this amplifier works, and encountering such breakdowns, it will be easier to solve the problem.

Vacuum amplifier

If the engine speed drops when the brake is pressed, the vacuum amplifier or its component parts is the cause. Often, this problem happens because of the design features of this mechanism and the principle of its operation. This mechanism is in a round closed case. It is located under the hood, near the brake pedal. The master cylinder is connected to the body. The main task of this unit is to reduce the pressure on the pedal when the speed is reduced. At the heart of the amplifier is the diaphragm.

Diaphragm

This part is quite elastic and strong at the same time. It is made of modern polymer materials on a polyurethane basis. In the central part of the diaphragm there is a piece of steel in the form of a circle, in which two stems on opposite sides rest. One of these elements is connected to the pedal. The second is with the main brake cylinder. The diaphragm divides the body into two parts. One of these parts is vacuum. It is located on the side of the master cylinder. The second is the atmospheric half and is on the other side. The vacuum brake booster is sealed. Its body with a diaphragm inside zavaltsovan. The two halves are connected to each other by means of a working valve. The brake pedal is used as a drive for this valve.

Principle of operation

The main task of the amplifier is to maintain the vacuum in the two communicating chambers at the moment when the valve is open and do not press the brake. If you press the pedal, the element closes. In this case, in the part responsible for vacuum, there will be a powerful rarefaction. In order to obtain this rarefaction, a pipeline leading to the intake manifold of the power unit is fed to the choke of the chamber. Also in the design of the mechanism is a return spring. It returns the diaphragm to its normal position. When the driver first presses the pedal, the valve closes. If you continue to press, an air hole will appear in the atmospheric chamber and air will enter there. The pressure inside the chamber is 760 mm Hg. Art. Due to rarefaction, the pressure on the master cylinder rod will increase, and therefore the braking efficiency will increase. This principle of the amplifier is relevant only for gasoline engines. On diesel it is impossible to get a vacuum in this way. Therefore, automakers equip the amplifiers for diesel units with special pumps.

Crankshaft and braking force feedback

As already noted above, the vacuum amplifier is in direct connection with the intake manifold. Therefore, any violation of the integrity of the reservoir will adversely affect the quality of the air-fuel mixture that enters the engine cylinders. A mixture of air and fuel, where there is not enough oxygen, will not burn completely. Therefore, the power unit loses power and efficiency. That's why when you press the brake pedal, the rpm falls.

Methods of diagnosis

If you experience similar problems while using your vehicle, you should immediately find out what the malfunctions are. The fact is that the situation when when you press the brake, the rpm falls, very unpleasant. If in the beginning only slightly falls speed, then after a while the engine just stalls with light touch of the brake pedal. This can happen at the most inopportune time. Let's notice, what even in completely serviceable car turns fall at pressing a brake, but this falling insignificant. This happens because of the design of the amplifier.

Hose

When the drop in the speed is quite significant, then it is necessary to visually inspect the hose connecting the amplifier and the intake manifold to the engine. If the tube has visible damage, and this can be various cracks or tears, then the integrity of the reservoir is impaired. What in the end? The process of the normal preparation of the fuel mixture is changing, which is why the stable operation of the engine is disturbed. That's why when you press the brake pedal, the speed falls and the engine stalls. If there is damage on the hose, it is recommended to replace it. And then the problem will be solved. If the tube is ideal, you should look for air sucking in the manifolds and in the vacuum amplifier itself. If this does not help to solve the problem, then the reason is worth searching in the amplifier itself. But it must be remembered that it will not be possible to repair the vacuum mechanism of the braking force. It is non-repairable, and therefore the issue can only be solved by a complete replacement.

Typical vacuum amplifier faults

Before talking about the malfunctions of this system, it should be noted that the failure of the mechanism does not completely disable the system. The brakes will work, but to drive a car with a faulty amplifier, you will have to apply more effort to reduce the speed. In this case, when the brake is pressed, the speed falls. One of the most popular breakages is the rupture of the hose. From under the hood, you will hear a characteristic hiss. What to do in this case, has already been mentioned above. Also, breakdowns inside the amplifier mechanism are possible. The valve may be damaged. During operation, it hardens, and due to the wear of rubber, the diaphragm and the elastic partition can collapse.

Diagnosis of the vacuum amplifier

So, if you notice a drop in speed when you press the brake, then first thing is to check the amplifier for serviceability. Of course, you can go to a specialist in carburettors. But the problem of falling turnover is unlikely to solve. If there is a depressurization, this will result in air entering the intake manifold. As a result, the turns fall when the brake is pressed. The fuel-air mixture is sharply impoverished. There is also another way to diagnose. The brake pedal is pressed up to six times on the muffled engine. Then the pedal is fixed in the middle position and the motor is turned on. When the pedal falls through the startup process, then the amplifier is OK. If it remains in the same position, you should pay special attention to the element. At visual inspection it is necessary to search for stains on the case and the reason for streaks.

Replacement of the vacuum amplifier

The replacement of this mechanism is simple enough with the necessary tools. In various cars, it may be necessary to dismantle the expansion tanks. During the operation, remove the brake cylinder, and then the amplifier itself. In terms of time it takes about three hours.

Summary

A vacuum amplifier is an important thing to do in any car. He makes the process of braking easy and at ease. That's why when you press the brake, the revolutions fall. The reason is in a faulty amplifier or system failure.