Question 1

How to test and replace the Brake Booster servo unit on Audi A3?

Accepted Answer

In order to test the brake booster, press the footbrake a few times to deplete the vacuum, then upon starting the engine, press the pedal to the floor; one should have a feel of the brake pedal giving in as the vacuum fills in supply. Let the engine run for a minimum of two minutes and then turn it off. When the brake pedal does not get hard when stepped on the first time but becomes stiffer every time the brake pedal is used, then the brake booster is working well. In case it does not work, examine the brake booster non-return valve and, in diesel models, the vacuum pump. If the brake booster does not work satisfactorily, then it should be replaced because it cannot be repaired. The brake booster may be removed by first disassembling the master cylinder, followed, where necessary, by the heat shield and the vacuum hose of the sealing grommet. Uncouple the wiring to the brake booster vacuum sensor (where fitted), remove the retaining circlip, and dislodge the sensor. With LHD models and a manual transmission, the gearchange cables are to be disconnected, and the gearchange support bracket is to be unbolted and tied up. Eliminate the lower side of the driver facia panel and the lower side of the dash panel. On models produced prior to the end of 2005, the brake light switch is found to be located on the pedal bracket and is to be removed. When installed, loosen the retaining screws and unscrew the connection plate between the brake and clutch pedals, and also take away the air duct and cover so that the brake booster mounting nuts can be accessed. Attach a special tool or a suitable alternative to release the brake pedal from the brake booster pushrod off the ball with a special tool in place of the plastic lugs, which are tough. Loosen the nuts holding the brake booster to the bulkhead and then push the unit out of place, retrieving the gasket where used. Clearing of the inlet manifold may be required on some of the RHO models. To refit, inspect the vacuum hose sealing grommet to see if it is damaged and fit a replacement gasket to the rear of the brake booster and re-fit it in the engine compartment. Make sure that the brake booster pushrod is properly seated in the brake pedal, press the pedal on the pushrod ball, and reassemble and tighten the mounting nuts to the required torque. Install the connecting plate, air duct, and cover back in place where necessary, and on models built prior to late 2005, replace the brake light switch again. Refit the facia trim panels, and on LHO models with manual transmission, refit the gearchange cables and support cable. Ease the vacuum hose firmly back in the correct position, ensuring that the sealing grommet has not been shifted around, and reattach the heat shield and, where necessary, the vacuum sensor and wiring. Lastly, install the master cylinder again, and on RHO models, install the inlet manifold again, should it be missing. When it is completed, start the engine and inspect for air leaks at the vacuum hose-to-brake booster connection and the functioning of the braking system.

Question 2

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

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 Brake Booster

69 Brake Boosters found

Audi Power Booster Part Number: 5Q1-614-106-R

Audi Booster Assembly Part Number: 80A-612-107-A

Audi Booster Assembly Part Number: 5Q1-614-106-N-REP

Audi Booster Assembly Part Number: 5Q1-614-106-Q

Audi Booster Assembly Part Number: 4M0-612-107-G

Audi Power Booster Part Number: 4K0-612-107-C

Audi Power Booster Part Number: 5N1-614-106-C-REP

Audi Booster Assembly Part Number: 8V1-612-107-A

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

Audi Booster Assembly Part Number: 1K1-614-106-A

Audi Booster Assembly Part Number: 4K0-612-107-F

Audi Booster Assembly Part Number: 1K1-614-106-AA

Audi Brake Booster Part Number: 5N1-614-106-B

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

Audi Booster Assembly Part Number: 8S1-612-107-B

Audi Power Booster Part Number: 4G0-612-107-D

Audi Booster Assembly Part Number: 36A-612-107-B

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

Audi Booster Assembly Part Number: 8E0-612-107-L

Audi Brake Booster Part Number: 4N0-612-107-D

Audi Brake Booster

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