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Brake Booster Replacement
 
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Pelican Technical Article:

Brake Booster Replacement

Steve Vernon

Time:

5 hours5 hrs

Tab:

$500

Talent:

***

Tools:

13mm deep socket, universal joint and extensions, 13mm wrench, trim removal tool, E12 socket, T20 Torx, fluid remover, 12mm flared nut wrench, rags or paper towel

Applicable Models:

Mercedes-Benz C250 (2012-14)
Mercedes-Benz C300 (2008-14)
Mercedes-Benz C350 (2008-14)

Parts Required:

New brake booster, gaskets, 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 comprise 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. Check your vacuum and lines before replacing the booster as the booster is not cheap.

Replacing the brake booster on the W204 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 along with the brake booster, which means opening the brake lines.

When you are finished you will need to completely bleed the brakes. DO NOT drive the car without completely bleeding the brakes.

Begin by removing the wiper arms (red and yellow arrows).
Figure 1

Begin by removing the wiper arms (red and yellow arrows). Please see our article on wiper arm removal for additional assistance.

Next, you will need to remove the cowl or rain diverter.
Figure 2

Next, you will need to remove the cowl or rain diverter. There are four plastic push/pull clips on the cowl or rain diverter (red arrows).

Use a trim removal tool and carefully pry the pin out from the base.
Figure 3

Use a trim removal tool and carefully pry the pin out from the base. Then pull the whole clip out.

The cowl or rain diverter clips into a metal channel (red arrow) on the bottom of the windshield.
Figure 4

The cowl or rain diverter clips into a metal channel (red arrow) on the bottom of the windshield. Start at one side and carefully lift the plastic cowl up and out from the windshield (yellow arrow).

There is a brace (yellow arrow) from the top of the left wheel well that mounts on two studs under the windshield (green arrows).
Figure 5

There is a brace (yellow arrow) from the top of the left wheel well that mounts on two studs under the windshield (green arrows). Use an E12 and remove the single bolt (red arrow). This will allow you to lift the brace. From there it simply pulls straight off the studs under the windshield.

You are going to need to remove the master cylinder from the booster if you are replacing the booster so I prefer to remove the master cylinder and reservoir first.
Figure 6

You are going to need to remove the master cylinder from the booster if you are replacing the booster so I prefer to remove the master cylinder and reservoir first. It is easier, cleaner and saves time in the long run. Begin by cleaning around the top of the reservoir, and remove the cap (red arrow).

Disconnect the fluid level sensor (red arrow).
Figure 7

Disconnect the fluid level sensor (red arrow).

Use some form of fluid pump or turkey baster, and remove as much fluid as you can from the reservoir.
Figure 8

Use some form of fluid pump or turkey baster, and remove as much fluid as you can from the reservoir.

Use a T20 Torx, and remove the single screw under the reservoir that holds it to the master cylinder (red arrow).
Figure 9

Use a T20 Torx, and remove the single screw under the reservoir that holds it to the master cylinder (red arrow). It is a tight fit so you may need to remove the fuse box lid to give you a little more room to work. With the screw removed wiggle and pull the reservoir straight up and out from the master cylinder. Even though you have removed the fluid there will still be some in the system so be prepared to catch it and dispose of it correctly. The O-rings between the reservoir and master may stay in the master or with the reservoir but you are going to replace them anyway.

You are going to be removing the brake lines from the master cylinder so make sure you use the proper wrench.
Figure 10

You are going to be removing the brake lines from the master cylinder so make sure you use the proper wrench. The fittings on the end of the lines are very soft. You can easily round them off if you use a standard wrench. Be smart and make sure to get and use a 12mm flared nut wrench.

Use the 12mm flared nut wrench and remove the two lines (red arrows).
Figure 11

Use the 12mm flared nut wrench and remove the two lines (red arrows). You can see there is still fluid in the master cylinder (yellow arrows).

Use a 13mm socket and a universal and extension for the right side nut, and remove the two 13mm nuts holding the master cylinder to the booster (red arrows).
Figure 12

Use a 13mm socket and a universal and extension for the right side nut, and remove the two 13mm nuts holding the master cylinder to the booster (red arrows).

When installing the master to the new booster make sure to replace both the O-ring between the booster and master (yellow arrow) as well as the two between the reservoir and master (red arrows).
Figure 13

When installing the master to the new booster make sure to replace both the O-ring between the booster and master (yellow arrow) as well as the two between the reservoir and master (red arrows). While it is almost impossible to install incorrectly make sure the pin in the booster goes inside the pump shaft (green arrow) in the master cylinder.

Pull the vacuum line from the booster (red arrow).
Figure 14

Pull the vacuum line from the booster (red arrow).

Take the lid off the fuse box and pry out the wring connection from the reservoir (red arrow), and disconnect the wiring from the box.
Figure 15

Take the lid off the fuse box and pry out the wring connection from the reservoir (red arrow), and disconnect the wiring from the box. This will give you more room to get the booster out.

Next, move to the inside of the vehicle, and remove the lower kick panel by removing the three T20 Torx screws (red arrows) along the front of the panel and the Philips head screw holding the hood release in place (yellow arrow).
Figure 16

Next, move to the inside of the vehicle, and remove the lower kick panel by removing the three T20 Torx screws (red arrows) along the front of the panel and the Philips head screw holding the hood release in place (yellow arrow). Drop the panel down, and disconnect any lights or wiring and remove the panel.

Remove the brake light switch; please see our article on brake light switch replacement for additional assistance (red arrow).
Figure 17

Remove the brake light switch; please see our article on brake light switch replacement for additional assistance (red arrow).

Remove the cover over the brake pedal assembly by gently prying the four clips out and removing the cover (red arrow).
Figure 18

Remove the cover over the brake pedal assembly by gently prying the four clips out and removing the cover (red arrow).

Use a 13mm wrench, and remove the brake pedal clevis pin (yellow arrow) that connects the brake pedal to the booster (red arrow).
Figure 19

Use a 13mm wrench, and remove the brake pedal clevis pin (yellow arrow) that connects the brake pedal to the booster (red arrow).

You will need a deep 13mm socket, as the two nuts holding the brake booster in place sit on long studs.
Figure 20

You will need a deep 13mm socket, as the two nuts holding the brake booster in place sit on long studs. It is a tight fit under the dash but the nuts are reasonably accessible. Use the 13mm deep socket, and remove the two nuts (red arrows, one shown).

You can now go back to the booster, and remove it from the vehicle.
Figure 21

You can now go back to the booster, and remove it from the vehicle. Installation is the reverse of removal. Do not forget that you MUST bleed your brake system before driving the car.

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