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Audi A4 Brake Booster Replacement
 
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Pelican Technical Article:

Audi A4 Brake Booster Replacement

Steve Vernon

Time:

5 hours5 hrs

Tab:

$300

Talent:

***

Tools:

T20 Torx, E10Torx, 2 adjustable wrenches, 13mm flare nut wrenches, power bleeder, Audi scan tool

Applicable Models:

Audi A4 (2002-05)
Audi A4 Cabriolet (2003-06)

Parts Required:

New brake booster, brake fluid

Hot Tip:

Use paper towels and plastic bags to contain any fluid leaks

Performance Gain:

Better braking

Complementary Modification:

Replace master cylinder

Without a doubt, your brakes are the most important system on the car. The heart of the brake system is the master cylinder, which controls the brake hydraulic pressure of the entire system. The brake pedal or more specifically the effort used when pressing on the brake pedal is assisted by a brake booster. The brake booster is a sealed container with a large rubber diaphragm inside. The booster uses vacuum pressure from the engine to assist in the pedal effort. If you are experiencing increased effort on the pedal to slow the car or any form of differing pressure when braking, it may be the booster going bad. There are many components involved with generating and maintaining the vacuum pressure for and in the booster, so make sure to check them all before replacing the booster, as the booster is not cheap.

Replacing the brake booster on the Audi A4 is not difficult. It is just a tight fit, but it should take no more than five hours including bleeding the brakes. Note: you will need to remove the brake master cylinder with the brake booster, which means opening the brake lines. Be sure you have an Audi scan tool, as you will need to put the ABS control unit into bleed mode to properly bleed the brakes.

When you are finished, you will need to completely bleed the brakes. DO NOT drive the car without completely bleeding the brakes. You will need the Audi scan tool to put the ABS system into bleed mode.

Begin by removing the cowl and battery cover from the area just below the windshield; it just pulls off (red arrow).
Figure 1

Begin by removing the cowl and battery cover from the area just below the windshield; it just pulls off (red arrow).

With the cover off you can see the reservoir and cap (green arrow) and where the master cylinder attaches to the brake lines (red arrow).
Figure 2

With the cover off you can see the reservoir and cap (green arrow) and where the master cylinder attaches to the brake lines (red arrow). If you have a manual transmission, there will be a line coming out of the left side of the reservoir to feed the clutch hydraulics.

Begin by sucking out as much fluid as you can.
Figure 3

Begin by sucking out as much fluid as you can. Use a turkey baster or fluid pump and suck as much fluid as possible out (red arrow). You will not be able to get all the fluid out so be prepared for some spillage. Remember, if you get any fluid on your hands, gloves or clothes and touch your paint, you will quickly ruin your paint job. Use caution and work carefully.

There is a long screw that holds the reservoir to the master cylinder.
Figure 4

There is a long screw that holds the reservoir to the master cylinder. It is located below the reservoir and can be difficult to get at. Our car needed a T20 Torx to remove it (red arrow). You will need to remove the reservoir to get access to the mounting bolts for the booster.

Use care when removing the screw, as you do not want to drop it down into the vehicle (red arrow).
Figure 5

Use care when removing the screw, as you do not want to drop it down into the vehicle (red arrow).

Before removing the reservoir clean around the master cylinder, especially if you are only replacing the reservoir.
Figure 6

Before removing the reservoir clean around the master cylinder, especially if you are only replacing the reservoir. You do not want any dirt or debris getting into the master (red arrow). Gently pry the reservoir off of the master cylinder. It is only held in place by the two plastic nubs on the bottom of the reservoir sitting in the rubber grommets in the master. Wiggle and pry it up and it will pop out. You will need to remove the brake fluid level sensor (yellow arrow) before you remove the reservoir from the vehicle.

If you are only replacing the reservoir, make sure to replace the grommets as well (red arrow).
Figure 7

If you are only replacing the reservoir, make sure to replace the grommets as well (red arrow). It is a good idea to cover the openings into the master at all times to make sure nothing can get in and destroy the master. If you are just replacing the reservoir from this point, installation is the reverse of removal. Remember, you cannot drive the vehicle until you have completely bled the system.

If you are replacing the master cylinder, you will need a 13mm flared nut wrench; this wrench will grab 5 sides of the line and prevent stripping the nut.
Figure 8

If you are replacing the master cylinder, you will need a 13mm flared nut wrench; this wrench will grab 5 sides of the line and prevent stripping the nut. If you round off a nut on a brake line, you will need to replace the entire line and the nuts cannot be replaced separately. Be smart and use the right tool for the job.

Remove the two lines coming out from the master cylinder (red arrows).
Figure 9

Remove the two lines coming out from the master cylinder (red arrows).

If you are replacing the master and especially if you are also replacing the booster, it is a good idea to completely remove the brake lines from the master cylinder to the ABS unit.
Figure 10

If you are replacing the master and especially if you are also replacing the booster, it is a good idea to completely remove the brake lines from the master cylinder to the ABS unit. You are going to need to bleed the system when you are done, so removing the lines will give you a lot more room to work and eliminate the possibility of damaging them. Clean around the lines and then use your 13mm flared nut wrench and remove the lines from the top of the ABS control unit (red arrows).

If you remove the ABS control unit brake lines, make sure to properly clean around the top and then plug the openings so no dirt or foreign matter can get into the unit (red arrows).
Figure 11

If you remove the ABS control unit brake lines, make sure to properly clean around the top and then plug the openings so no dirt or foreign matter can get into the unit (red arrows).

The lines are protected by a rubber grommet where they run through the sheet metal; remove the grommet with the lines (red arrow).
Figure 12

The lines are protected by a rubber grommet where they run through the sheet metal; remove the grommet with the lines (red arrow).

The master cylinder is attached to the booster by an E10 Torx bolt (red arrow) inside of the 22mm nut (yellow arrow).
Figure 13

The master cylinder is attached to the booster by an E10 Torx bolt (red arrow) inside of the 22mm nut (yellow arrow). The nut holds the master cylinder to the booster, while the E10 Torx bolt holds the master to the firewall.

Use an E10 Torx and remove the two long bolts holding the booster to the firewall (red arrows).
Figure 14

Use an E10 Torx and remove the two long bolts holding the booster to the firewall (red arrows). You will be able to fully remove the top bolt but the bottom bolt will stay loosely in the booster, as there is not enough room to remove it. If you need extra room to get the booster and master out from the engine area, you can also remove the two 22mm nuts holding the master to the booster and free everything up.

You will need to remove the rod from the booster connecting to the brake pedal inside the vehicle.
Figure 15

You will need to remove the rod from the booster connecting to the brake pedal inside the vehicle. Begin by removing the lower drivers' side storage compartment (red arrows). Please see our article on drivers' side lower storage compartment removal for additional information.

The booster rod sits in a plastic clip in the brake pedal (red arrow).
Figure 16

The booster rod sits in a plastic clip in the brake pedal (red arrow).

Audi makes a special tool for removing this, but you can stick two small flathead screwdrivers between the ball on the end of the rod separating the clips and then pull the rod from the plastic retainer (red arrows).
Figure 17

Audi makes a special tool for removing this, but you can stick two small flathead screwdrivers between the ball on the end of the rod separating the clips and then pull the rod from the plastic retainer (red arrows).

There is very little room to work under the pedals.
Figure 18

There is very little room to work under the pedals. Some people find it easier to use two adjustable wrenches and separate the locking nut on the booster bar and then unscrew it from the end of the rod in the plastic retaining clip in the brake pedal (green arrow). Once the rod is free, you can remove the booster and master cylinder from the vehicle. It may take some wiggling and a few different angles but it will come out.

Make sure when installing the master cylinder that the push rod is installed correctly in the master cylinder and always replace the rubber sealing O-ring on the master.
Figure 19

Make sure when installing the master cylinder that the push rod is installed correctly in the master cylinder and always replace the rubber sealing O-ring on the master. Next, you will want to carefully install the booster rod (yellow arrow) into the opening to the pedal box (green arrow). Make sure to have at least the lower E10 Torx bolt installed in the booster (red arrows), or you will be removing it again, as there is not room to install the bolt once the booster is in place. Reinstall everything and bleed the brakes. DO NOT drive your car until you have completely bled your brakes! You will need the Audi scan tool to put the ABS system into bleed mode.



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Comments and Suggestions:
mulenga Comments: Kindly send me price for brake booster for Audi Quattro 2002
October 30, 2016
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