The failure of the brake booster does not mean a loss of brake efficiency, only an increase in the pedal effort required for the same braking efficiency.
The brake booster receives the vacuum required for its operation (vacuum) through the vacuum line from the intake manifold. The performance of the brake booster can be checked as follows:
With the engine off, press the brake pedal several times until all the vacuum is out of the system.
Press the pedal with medium force and start the engine.
If the brake booster is working properly, the brake pedal will drop noticeably. The brake booster cannot be removed by simple means; special tools used by Audi must be used to separate the brake pedal from the push rod. Only with these devices, you can read the further description.
Remove trim from driver's side.
Remove the brake fluid reservoir as described above. To do this, remove the clutch hydraulic hose (3), plug connection (2) and a tank (1). The tank must be removed by shaking back and forth.
The following steps must be carried out, guided by the figure below.
First you need to disconnect both brake lines (2), pull them out and carefully bend them to the side. Wipe up leaking brake fluid with a cloth. Disconnect the vacuum hose from the side (3) from the brake booster. Now unscrew the mounting bolts (1). This requires a Torx T45 head with an extension.
Next, the push rod of the brake booster pusher is disconnected from the pedal, which is associated with the already mentioned difficulties. Remove the brake light switch first. If cruise control is installed (Cruise control), then you need to remove the intake air valve nearby. The switch and valve must be installed in a certain way.
Now install special tool No. 3289 on the pedal. The push rod of the brake booster is removed from the pedal. Pull the brake pedal back to complete the removal.
Pull the brake booster together with the brake master cylinder out of the casing.
Attention: The master brake cylinder can also be removed in advance, as already described above. If necessary, unscrew the two flange nuts.
Installation is made in an order, the return to removal. If a new brake booster is to be fitted, the pushrod length must be re-adjusted. In this case, the distance between the mounting surface of the brake booster and the end of the pusher rod is measured, indicated as (A). Since the push rod can move, care must be taken to ensure that it is perpendicular to the amplifier. In addition, there should not be a gasket when measuring. If it is nevertheless stuck, then when measuring it is necessary to take into account its thickness.
To adjust, loosen the locknut and move the push rod. After adjustment, tighten the locknut.
Replace the gasket and reinforce the brake booster again. Bolts may not be replaced.
Lightly lubricate the pivot pin and repair the brake pedal/pushrod connection.
If the brake cylinder has been removed, replace the flange nuts (50 Nm). Tighten union nuts of pipes to 15 Nm.
The non-return valve located in the brake booster can be the cause of a malfunction in the system. To check, you can carefully squeeze out the valve with a screwdriver and blow it in the direction of the arrow that is on the valve. Air must come out the other side. If you blow from the other side, then the air should not come out. When replacing the valve, it is necessary to choose the same one that was previously installed. The valve is pressed into the brake booster.
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