22.3. Pumping of the hydraulic brake system

Prevention

The brake fluid used in hydraulic system of coupling is poisonous therefore at its hit on skin it is necessary to wash out immediately this place a plentiful amount of water. If liquid got into eyes or in an organism, it is necessary to see a doctor immediately. Some liquids have property to ignite easily and can light up even from contact with hot knots of the car. Besides, the liquid used in hydraulic system of coupling dissolves paint and plastic therefore at hit of liquid on a paint and varnish covering of the car wash out it a plentiful amount of water. Also this liquid is hygroscopic, i.e. absorbs moisture from air and therefore the liquid which is stored a long time in open ware is not recommended to be used.

Removal of air from a back brake support

Pumping of hydraulic system of brakes is necessary for removal of air which considerably reduces efficiency of braking. Air can get to hydraulic system owing to depressurization of system at repair, replacement of separate knots or brake fluid. Points the increased course of a pedal of a brake and its softness to availability of air in the drive. Before removal of air check tightness of all knots of the drive of brakes and their connections.

Never reuse brake fluid.

When performing operation of pumping of the brake system do not allow the level of brake fluid to fall below the middle of a tank.

If brake fluid left system because of leak in system, find the reason and eliminate leak before further actions.

If the hydraulic system was separated partially, and the corresponding precautions were accepted to prevent further loss of liquid, it is possible to pump over only a part of system.

Pumping can be carried out with the assistant or independently, a set of pumping of the brake system. Always act according to the instruction. It is recommended to use a set everywhere where perhaps as it very much simplifies the procedure of pumping. If there is no set for pumping, it is necessary to stock up with the pure capacity and a transparent plastic tube of the corresponding length which has to put on densely on the pumping union. At the same time the help of other person will be required.

Sequence of pumping

If only partial connection of the hydraulic brake system was made and the corresponding precautions were observed, then it is enough to pump over only this part of system.

Carry out pumping of all system of the drive of brakes in the following sequence:

– right back wheel;
– left back wheel;
– right forward wheel;
– left forward wheel.

Prevention

On models with a control system of the speed of the movement (ASR) if the hydraulic system, the main brake cylinder, the hydraulic block, the hydraulic pump and the accumulator was under repair, then it is also necessary to pump over the hydraulic system tank.

Pumping – the main method (two persons)

Remove a dustproof cap from the union of pumping of the wheel cylinder, clear it and dress on it a pure transparent hose which other end lower in the capacity which is partially filled with brake fluid. Capacity has to be at least 300 mm above the pumping union. Thanks to it hit of air in the cylinder through a pumping union carving is prevented. Sharply press a pedal of a brake of 3 - 5 times with an interval 2 – 3 seconds, unscrew on a turn floor the pumping union at the pressed pedal. Continuing to press a pedal, force out the liquid which is in system together with air through a hose in capacity. After the pedal will reach extreme forward situation, and the liquid effluence through a hose will stop, screw the pumping union to the full. Repeat these operations, the air outlet from a hose will not stop yet.

Holding a pedal in the pressed situation, screw up the pumping union against the stop and remove a hose.

Wipe the union of pumping and establish a protective cap.

Repeat these operations for other wheels.

Prevention

During removal of air constantly you monitor availability of brake fluid in a tank, without allowing an exposure of its bottom as at the same time air will get to system again.

At absence the pedal has to pass about a half of the course in system of brakes of air. To exclude influence of the vacuum amplifier of brakes on pumping of brakes, you make removal of air at the idle engine.

Pumping – use of a set with the unidirectional valve

The set consists of a tube with the unidirectional valve installed on it which excludes a possibility of return to the brake system of remote brake fluid with vials of air. On some sets the transparent container in which vials of air in brake fluid (see rice are well looked through is established. Removal of air from a back brake support).

Remove a dustproof cap from the union of pumping of the wheel cylinder, clear it and dress on it a hose from a set. Unscrew the pumping union on a half of a turn. Smoothly press a brake pedal against the stop and slowly release it in a starting position. Repeat this operation until from the union of pumping there is no brake fluid without vials of air.

Tighten the pumping union against the stop, pick up from it the phone and dress a dustproof cap.

Prevention

During removal of air constantly you monitor availability of brake fluid in a tank, without allowing an exposure of its bottom as at the same time air will get to system again.

Pumping – use of a set of pumping under pressure

Use of a set of pumping under pressure demands giving to it compressed air for what it is possible to use the beefy tire of a spare wheel. Reduce pressure in the tire up to the size specified in the maintenance instruction of a set.

Prevention

Mercedes-Benz recommends to use the compressed air given under pressure of no more than 2 bars.

Connect the container filled with brake fluid to a popolnitelny tank of the main brake cylinder. Process of pumping begins after unscrewing of the union of pumping on a half of a turn. After when the effluence of brake fluid with vials of air stops and only pure brake fluid will follow, screw up the pumping union against the stop.

When pumping by this method a large amount of liquid is necessary for a hydraulic system to prevent hit of air in the main brake cylinder in the course of pumping that often occurs if liquid level in a tank is not supported.

Pumping by pressure is especially effective when the system is difficult for pumping or when full pumping of system is carried out during usual replacement of brake fluid.

All methods

After completion of process of pumping strongly press a brake pedal, at the same time it has to pass about a half of the course. Wash away all traces of the spilled brake fluid and tighten pumping unions the required moment, then establish on them dustproof caps.

Check the level of brake fluid in a popolnitelny tank of the brake system and, if necessary, add brake fluid.

Remote brake fluid should not be used more. Pure brake fluid has to be stored in a tight vessel, as it is very hygroscopic that lowers temperature of boiling and worsens technical characteristics of brake fluid.