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Pelican Technical Article:

Brake Master Cylinder Removal

Kerry Jonsson

Time:

2 hours2 hrs

Tab:

$250

Talent:

***

Tools:

11mm line wrench, 13mm socket with ratchet and extension

Applicable Models:

Mercedes-Benz R129 (1990-02)

Parts Required:

Brake master cylinder, brake fluid

Hot Tip:

Put paper towels under the master cylinder to catch dripping brake fluid.

Performance Gain:

Fix failed master cylinder and restore braking

Complementary Modification:

Flush brake fluid at the same time
As you apply your brake pedal a piston inside the master cylinder compresses a chamber filled with brake fluid. This fluid travels through brake lines and brake hoses to reach the brake calipers. The caliper pistons are forced out and force the brake pad into the brake rotor. When you release the brake pedal the piston in the master cylinder returns to its normal position. As the brake pads wear and the volume of the system becomes larger the master cylinder draws in additional fluid from the master cylinder fluid reservoir. A low fluid level may mean your pads are low or you have a leak in the system. Think of how many times you apply and release your brakes. This back and forth motion eventually wears the seals on the master cylinder piston out. Now it is rare for a master cylinder to totally fail but these contaminants get into the brake fluid and can cause the brake pistons to start sticking in the caliper and solenoids to stick in the ABS control unit. In this tech article we will remove the brake master cylinder to accommodate the installation of a new brake master cylinder.
With the brake fluid reservoir cap already removed, remove the strainer.
Figure 1

With the brake fluid reservoir cap already removed, remove the strainer.

Use a suction tool to empty out the brake fluid reservoir as much as you can.
Figure 2

Use a suction tool to empty out the brake fluid reservoir as much as you can.

Squeeze the two locking tabs on the brake fluid level sensor and pull the connector off of the reservoir.
Figure 3

Squeeze the two locking tabs on the brake fluid level sensor and pull the connector off of the reservoir.

Using an 11mm line wrench, remove the rear brake line from the master cylinder.
Figure 4

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

Using an 11mm line wrench, remove the front brake line from the master cylinder.
Figure 5

Using an 11mm line wrench, remove the front brake line from the master cylinder. You can save this step for later if the fitting is too tight since there is little access to utilize a wrench. You can remove this fitting after we have removed the brake fluid reservoir. Depending on the tools you have you may not have to remove the brake fluid reservoir. We will cover this in later steps.

Once you have loosened the fitting with the line wrench you can use a regular wrench to thread it all the way out.
Figure 6

Once you have loosened the fitting with the line wrench you can use a regular wrench to thread it all the way out.

Using a pair of pliers, squeeze down on a lower section of the hose and pull the hose downward to remove it from the reservoir.
Figure 7

Using a pair of pliers, squeeze down on a lower section of the hose and pull the hose downward to remove it from the reservoir.

Remove the upper 13mm fastener (green arrow) that mounts the brake master cylinder to the brake booster.
Figure 8

Remove the upper 13mm fastener (green arrow) that mounts the brake master cylinder to the brake booster.

Remove the lower brake master cylinder 13mm fastener (green arrow) if you have a long extension and swivel.
Figure 9

Remove the lower brake master cylinder 13mm fastener (green arrow) if you have a long extension and swivel. In our case there is a bracket around the fastener that was bent outward. We decided to remove the brake fluid reservoir.

Remove the brake fluid reservoir by pulling straight up on it until it detaches from the grommets.
Figure 10

Remove the brake fluid reservoir by pulling straight up on it until it detaches from the grommets. Some brake fluid will leak out so be prepared with some paper towels or rags for clean up.

With the brake fluid reservoir removed, we can clearly see the bracket (green arrow) blocking the 13mm fastener that also mounts the brake master cylinder to the brake booster.
Figure 11

With the brake fluid reservoir removed, we can clearly see the bracket (green arrow) blocking the 13mm fastener that also mounts the brake master cylinder to the brake booster.

I have decided to remove the bracket.
Figure 12

I have decided to remove the bracket. Remove the 5mm fastener (green arrow) that mounts the bracket to the brake master cylinder. Normally this would have come off with the brake master cylinder and we would have disassembled it with the brake master cylinder outside of the car.

Move the bracket out of the way and remove the 13mm fastener (green arrow).
Figure 13

Move the bracket out of the way and remove the 13mm fastener (green arrow).

Using a 19mm wrench remove the brake booster vacuum supply hose.
Figure 14

Using a 19mm wrench remove the brake booster vacuum supply hose.

Lift the engine compartment seal out of the way of the vacuum supply line for the brake booster.
Figure 15

Lift the engine compartment seal out of the way of the vacuum supply line for the brake booster.

Lift up on the brake booster vacuum supply line grommet to remove it from the fire wall.
Figure 16

Lift up on the brake booster vacuum supply line grommet to remove it from the fire wall.

Slightly bend the brake lines out of the way.
Figure 17

Slightly bend the brake lines out of the way. Do not move them too much otherwise they will be harder to line up and thread in during installation. Slide the brake master cylinder forward until you can pull it out of the car. Installation is the reverse of the removal procedures. Bench bleed the new brake master cylinder first before installation. Install the new brake master cylinder and tighten it down. Attach the bracket for the lower pressure sensors with fastener. Install the two brake lines and the brake fluid reservoir. Plug in the brake fluid reservoir level sensor and fill the reservoir with new, clean brake fluid. Bleed the brake system according to our tech article on brake bleeding.

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Page last updated: Fri 12/9/2016 02:28:11 AM