Checking the brake booster (Mondeo 3)

ORDER OF EXECUTION

With the engine stopped, press the brake pedal several times and then hold it in the extreme position (until it stops).
Now start the engine. The pedal should go down a couple more millimeters. If this does not happen, there are the following reasons:
The low-pressure hose from the intake manifold to the brake booster is not sealed: in this case, be sure to replace the hose and check its connecting flanges.
Defective check valve in the low-pressure hose: To check the valve, disconnect the low-pressure hose from the booster and run the engine at idle. If you do not hear rhythmic intake noise, plug the free end of the hose with your fingertip. If a vacuum does not form in the hose after this, the valve is defective.
The rubber gasket between the master cylinder and the brake booster has become porous: remove the master cylinder from the booster and replace the sealing ring.
The air filter on the hydraulic booster lifter is dirty: disconnect the filter from the push rod using a wire hook. Install the new filter to the center point and clamp it around the lifter where it fits. Make sure the filter closes around the lifter, otherwise unfiltered air may enter the brake booster.
Defect in the amplifier membrane: repair is not possible here. It is necessary to fully get used to the idea of a new amplifier.

Basic design of a dual-chamber brake booster.

1 — Pressure rod (to the master cylinder),
2 - Pressure spring,
3 - Low pressure chamber with vacuum connection,
4 - Membrane with membrane plate,
5 — Working piston,
6 - Filling piston,
7 - Double valve,
8 — Valve body,
9 — Air filter,
10 — Piston connecting rod (from the brake pedal),
11 — Valve seat,
12 — Working chamber.

The original source of this article can be found at (FORDBOOK.RU)

This article is available at russian, bulgarian, belarusian, ukrainian, serbian, croatian, romanian, polish, slovak, hungarian

Article reviewed: Herman Ostrovsky

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Checking the brake system
Checking the brake fluid level
The structure of the braking system

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Checking the brakes for functionality
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Bleeding the brake system
Replacing brake fluid