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Brake Master Cylinder Replacement
 
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Pelican Technical Article:

Brake Master Cylinder Replacement

Kerry Jonsson

Time:

3 hours3 hrs

Tab:

$250

Talent:

**

Tools:

11mm line wrench, pliers, 13mm socket with ratchet and wrench, T25 Torx bit

Applicable Models:

Mercedes-Benz W211 (2003-09)

Parts Required:

Brake master cylinder

Hot Tip:

Wear gloves while working with brake fluid

Performance Gain:

Improved braking

Complementary Modification:

Flush brake fluid while you're at it

When you apply the brake pedal you are pushing a piston in the brake master cylinder that is full of brake fluid. This brake fluid is forced out of the master cylinder, through brake lines and brake hoses, to the calipers and forces the caliper pistons into the brake pads. When you release the brake the piston returns to its normal position. This back and forth motion eventually causes the brake master cylinder seals to wear out. The rubber particles from the seals become suspended in the brake fluid and can cause solenoids in the ABS unit to stick. Also, as the brake pads wear the volume of the brake system becomes larger as the caliper pistons stick out a bit to maintain the proper clearance with the brake rotor. As the volume of the brake system grows the brake master cylinder draws in brake fluid from its reservoir. A low fluid level in the reservoir would indicate either the brake pads are low or you have a leak in the system.

In this tech article we will go over the steps to replace your brake master cylinder.

ThisPicture illustrates the left side of the engine compartment at the brake master cylinder.
Figure 1

This picture illustrates the left side of the engine compartment at the brake master cylinder. Remove the black plastic cover to the brake fluid reservoir and remove the brake fluid reservoir cap.

Remove the filer screen from the fill opening in the brake fluid reservoir.
Figure 2

Remove the filer screen from the fill opening in the brake fluid reservoir.

Use a suction tool to draw the fluid out of the reservoir.
Figure 3

Use a suction tool to draw the fluid out of the reservoir.

Squeeze the locking tab of the brake fluid level sensor and unplug the connector by pulling it away from the brake fluid level sensor.
Figure 4

Squeeze the locking tab of the brake fluid level sensor and unplug the connector by pulling it away from the brake fluid level sensor.

Squeeze the upper hose clamp and slide it along the hose towards you.
Figure 5

Squeeze the upper hose clamp and slide it along the hose towards you.

Pull the hose off of the brake fluid reservoir.
Figure 6

Pull the hose off of the brake fluid reservoir.

Remove the engine compartment seal from the left side of the engine compartment.
Figure 7

Remove the engine compartment seal from the left side of the engine compartment.

Lift the engine wiring harness (green arrow) from its slot in the firewall.
Figure 8

Lift the engine wiring harness (green arrow) from its slot in the firewall.

Working below the brake fluid reservoir, remove the T25 Torx fastener (green arrow) for the brake fluid reservoir.
Figure 9

Working below the brake fluid reservoir, remove the T25 Torx fastener (green arrow) for the brake fluid reservoir.

Remove the brake fluid reservoir by lifting it straight up from the brake master cylinder.
Figure 10

Remove the brake fluid reservoir by lifting it straight up from the brake master cylinder.

Squeeze the lower hose clamp (green arrow) and remove the lower reservoir hose from the brake fluid reservoir.
Figure 11

Squeeze the lower hose clamp (green arrow) and remove the lower reservoir hose from the brake fluid reservoir.

Using an 11mm line wrench, remove the upper brake line from the brake master cylinder.
Figure 12

Using an 11mm line wrench, remove the upper brake line from the brake master cylinder.

Using an 11mm line wrench, remove the lower brake line from the brake master cylinder.
Figure 13

Using an 11mm line wrench, remove the lower brake line from the brake master cylinder.

ThisPicture illustrates under the left side of the dash board with the left side lower dash panel removed.
Figure 14

This picture illustrates under the left side of the dash board with the left side lower dash panel removed. See our tech article on left side lower dash panel removal. Twist the brake switch (green arrow) 90 degrees clockwise and remove the brake switch from its mount.

Push the locking tab (green arrow) and pull the upper plastic cover away from the locking tab.
Figure 15

Push the locking tab (green arrow) and pull the upper plastic cover away from the locking tab.

Then release the locking tab (green arrow) on the left side of the upper plastic cover away from the locking tab.
Figure 16

Then release the locking tab (green arrow) on the left side of the upper plastic cover away from the locking tab.

Pull the entire upper plastic cover from underneath the left side of the dashboard.
Figure 17

Pull the entire upper plastic cover from underneath the left side of the dashboard.

Working above the brake pedal, remove the 13mm fastener (green arrow).
Figure 18

Working above the brake pedal, remove the 13mm fastener (green arrow).

Working at the firewall behind the brake pedal, remove the three 13mm fasteners (green arrows).
Figure 19

Working at the firewall behind the brake pedal, remove the three 13mm fasteners (green arrows).

ThisPicture illustrates the left side of the engine compartment by the master cylinder.
Figure 20

This picture illustrates the left side of the engine compartment by the master cylinder. Move the brake lines slightly out of the way and start to pull the brake master cylinder out of the car. Unplug the brake booster electrical connector by squeezing the two locking tabs (green arrows) and pulling the connector away from the brake master cylinder.

Pull the brake master cylinder completely out of the car.
Figure 21

Pull the brake master cylinder completely out of the car. Installation is the reverse of the removal procedures. Fit the new master cylinder/booster assembly in its position on the firewall and tighten down the three fasteners. Attach the linkage to the brake pedal and tighten the fastener. Fit the inner lower cover and the brake switch. Install the lower dashboard cover. See our tech article on lower dash panel cover removal for further instructions. Plug in the electrical connector to the brake booster assembly. Fit and tighten both brake lines to the brake master cylinder. Attach the lower brake hose to the brake fluid reservoir and install the brake fluid reservoir into the two receptacles in the brake master cylinder. Tighten down the brake fluid reservoir hold down bolt and install the brake fluid filter screen. Plug in the brake fluid level sensor and attach the upper brake fluid reservoir hose. Fill the reservoir with brake fluid and bleed the brake system according to our tech article brake system bleeding.

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Page last updated: Mon 12/5/2016 02:29:37 AM