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Brake Master Cylinder and Reservoir
 
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Pelican Technical Article:

Brake Master Cylinder and Reservoir

Steve Vernon

Time:

2 hours2 hrs

Tab:

$250 to $400

Talent:

**

Tools:

13mm socket, Universal joint and extensions, T20 Torx, 12mm flare nut wrenches, power bleeder

Applicable Models:

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

Parts Required:

Master cylinder, reservoir, brake fluid

Hot Tip:

Use paper towels and plastic bags to contain any fluid leaks

Performance Gain:

Better braking

Complementary Modification:

Replace brake booster

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 hydraulic pressure of the entire system. Unfortunately, over many years, the master cylinder and reservoir have a tendency to wear out and leak. The leakage can occur internally or externally, resulting in a weakened braking system. If you have any problems with your brakes, and you think that it's related to the master cylinder or reservoir, you should probably replace it.

You will be opening the brake lines while replacing the master cylinder so you will need to completely bleed the system before driving the vehicle. Do NOT attempt to drive the vehicle before completely bleeding the system.

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 1

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.

Begin by cleaning around the top of the reservoir and remove the cap (red arrow).
Figure 2

Begin by cleaning around the top of the reservoir and remove the cap (red arrow).

Disconnect the fluid level sensor (red arrow).
Figure 3

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 4

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 5

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 cylinder may stay in the master cylinder or with the reservoir but you are going to replace them anyway.

With reservoir off you can see underneath it the two openings that supply the fluid to the master cylinder (red arrow) the bracket for the T20 screw (yellow arrow), and the closed off line (green arrow) to supply the hydraulic clutch on standard transmission cars.
Figure 6

With reservoir off you can see underneath it the two openings that supply the fluid to the master cylinder (red arrow) the bracket for the T20 screw (yellow arrow), and the closed off line (green arrow) to supply the hydraulic clutch on standard transmission cars. If you only need to replace the reservoir simply install the new one using a little brake fluid on the O-rings to ease the installation, and the rest is the reverse of removal. Do not forget to top up and bleed the brake system

You are going to be removing the brake lines from the master cylinder so make sure you use the proper wrench.
Figure 7

You are going to be removing the brake lines from the master cylinder so make sure you use the proper wrench. The fitting 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 8

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) along with the O-rings you will need to replace.

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 9

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).

Next, pull the master straight back and out from the booster (red arrow).
Figure 10

Next, pull the master straight back and out from the booster (red arrow).

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 11

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. Installation is the reverse of removal. Do NOT forget to fill and bleed the brake system.


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