brake fluid. Mercedes-Benz E-Class

REPAIR MAINTENANCE OPERATION OF MOTOR VEHICLES
Mercedes-Benz E-Class

general info. full specifications. diagnostics. hints. tips. tricks

Brake fluid - light yellow, poisonous, aggressive to paintwork, neutral to metal and rubber parts. Retains liquid even at -40 ?� C and has a very high boiling temperature - about +260 ?� C.

Lack of brake fluid - its absorbability. Water can penetrate into the brake fluid, such as moist air, - through a tank or a microscopic hole in the brake hoses and rubber sleeve. The content of water in the brake fluid not only causes corrosion of metal parts in the system, but also greatly affects the boiling point reduction. Even at 2.5% concentration of water boiling temperature is reduced to +150 ?� C. When a heavy load on the brakes this can be dangerous because the brakes are very hot. Near the heated brake fluid in the steam bubbles may be formed, which reduce the pressure in the system and can lead to the fact that when pressing the brake pedal is to "fall". In such cases, a few times quickly to press the brake pedal to increase the pressure in the hydraulic system.

A particularly dangerous effect of vaporization when the vehicle is parked after a sharp deceleration. In the absence of cooling ram air brake system working units heated even further, the maximum temperature is maintained for 15 minutes after the stop, and only after thirty minutes brake fluid cools down to normal temperature.

Driving the individual elements of the ABS system

Fig. 8.1. Driving the individual elements of the ABS: 1 - control; 2 - Front wheel brake with engine speed sensor; 3 - the hydraulic unit; 4 - brake master cylinder with an amplifier; 5 - parking brake mechanism; 6 - Brake rear wheel speed sensor with RPM

The plan provides for routine maintenance replacement of brake fluid every two years (the minimum requirement of the specification DOT 4). It should only use brake fluid recommended by the manufacturer for your model car.

Fig. 8.2. Installing the speed sensor on the front wheels 1 - a brake disk; 2 - the hub of the front wheel; 3 - the shield; 4 - a bolt with hexagon 25 Nm; 5 - speed sensor; 6 - knuckle

Fig. 8.3. Measuring wheel speed: 1 - speed sensor; 2 - coil; 3 - a magnetic core; 4 - toothed rotor; 5 - coaxial cable

Technical Dictionary

Anti-lock braking system (ABS)

The control unit ABS (Fig. 8.1).

Constantly processing information from the wheel speed sensors, and compares it with the programmed values. If the difference value indicates the danger of locking under braking one or more wheels, the control unit activates the hydraulic unit, which reduces the operating pressure of the brake on the wheel as long as it does not receive the free course and is again braked. Depending on the state of the road during one cycle inhibition passes within a few milliseconds.

The hydraulic unit.

This is the basic unit of ABS, installed in the front left of the engine compartment. It includes electric pump and valve unit with solenoid valves. When you press the brake pedal brake master cylinder pressure supplies brake fluid through the valve assembly to the wheels. This valve block controls the pressure in each of a hydraulic system, and integrating the front wheel located on a diagonal rear wheel. When the ABS control unit sends a command to an electrical signal, "reduce the fluid pressure." Brake fluid is in this case a small circle through the valve unit is fed back into the tank. The pump can be seen by the light pulsing of the brake pedal.

Wheel speed sensors.

Each sensor 5 (Fig. 8.2) is mounted on its wheel, at a short distance from the toothed disc (rotor pulses) fixed directly to the hub.

Toothed protrusions disc 4 (Fig. 8.3) depending on the wheel speed (speed) is faster or slower pass by the magnetic sensor core 3 1. Each tooth disc at passage 2 in the coil induces a brief increase in voltage. Its frequency depends on the rotational speed of the rotor and thus the wheel. By wire 5 coaxial electrical signal supplied to the control unit.

Thus, information on the wheel speed is transmitted as an electric signal to the control unit.

Anti-lock braking system

The relay.

For the work of the electric and magnetic valves meet the relevant relay. They are mounted on the holder under the block of management ABS.

Disturbances in the system ABS.

The warning lamp lights up the ABS system when the ignition is switched on and goes out when the engine is running, no later than 2 seconds. If the light stays on, it means that the ABS has a malfunction. Nevertheless, the movement can be continued - the brake will operate as a car without ABS. To eliminate the fault, contact the service center of Mercedes, where the start pinging control unit using a special device.