How is the power brake booster diagnosed, removed, and installed on Audi A4?

Question

Accepted Answer

On models equipped with an automatic transmission, a vacuum pump supplies vacuum to the power brake booster in addition to manifold vacuum, with the pump mounted near the ABS/ESP hydraulic unit and a vacuum hose routed to the brake booster; diagnosis by a dealer service department is required if the system appears defective. The master cylinder is removed along with the power brake booster as an assembly and separated afterward. For an operating check, depress the brake pedal several times with the engine off to ensure no change in pedal reserve distance, then start the engine and check for slight pedal movement, indicating normal operation. For an airtightness check, start the engine and turn it off after one or two minutes, then depress the brake pedal slowly; if the pedal depresses less each time, the booster is airtight. While the engine is running, depress the brake pedal, stop the engine with the pedal depressed, and if there's no change in pedal reserve travel after 30 seconds, the booster is airtight. Caution is advised as brake fluid can damage paint or finished surfaces, and the power brake booster is not serviceable; it should be replaced if defective. Begin removal by pressing the brake pedal several times with the engine off to remove stored vacuum, disconnect the negative battery terminal, remove the driver's side knee bolster, and detach the brake light switch. Next, detach the booster pushrod from the brake pedal, remove the engine cover, pull the check valve from the brake booster while leaving the vacuum hose attached, and remove as much fluid as possible from the reservoir. Unplug the electrical connector for the brake fluid level warning switch, remove the brake fluid reservoir retaining bolt, and detach the reservoir from the master cylinder. Clean the area around the brake line fittings thoroughly, detach the brake lines, and cap or plug all openings to prevent contamination. If equipped, remove the suspension cross-brace from above the booster, unscrew the booster mounting bolts until loose, and carefully remove the booster and master cylinder from the cowl compartment. Pull out the booster mounting bolts, remove the master cylinder mounting nuts, and detach the master cylinder from the power booster. For installation, if using a replacement brake booster, check and adjust the pushrod length as necessary, replace the O-ring seal between the master cylinder and power booster, and assemble the master cylinder to the power brake booster, ensuring correct pushrod alignment. The remainder of the installation procedures are essentially the reverse of removal, tightening all mounting fasteners to the specified torque values. To bleed the master cylinder on the vehicle, have an assistant pump the brake pedal several times slowly and hold it to the floor, loosening the line fittings one at a time to allow air and fluid to escape, repeating until the fluid is clear of air bubbles. Finally, bleed the brake system and test the operation of the brakes before putting the vehicle into normal service.

Genuine Audi A4 Brake Booster

9 Brake Boosters found

Audi A4 Booster Assembly Part Number: 8D0-612-107-B

Audi A4 Booster Assembly Part Number: 8W0-612-107-C

Audi A4 Booster Assembly Part Number: 8E0-612-107-J

Audi A4 Booster Assembly Part Number: 8K0-612-107-D

Audi A4 Booster Assembly Part Number: 8K0-612-107-C

Audi A4 Booster Assembly Part Number: 8E0-612-107-F

Audi A4 Booster Assembly Part Number: 4D0-612-107-B

Audi A4 Booster Assembly Part Number: 8K0-612-107-B

Audi A4 Pressure Metering Valve Part Number: 443-614-151-B

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