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Brake Master Cylinder Replacement
 
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Pelican Technical Article:

Brake Master Cylinder Replacement

Nick Czerula

Time:

2 hours2 hrs

Tab:

$150

Talent:

***

Tools:

11mm, 12mm line wrenches, 13mm universal socket

Applicable Models:

BMW X5 (2000-06)

Parts Required:

Brake fluid, brake cleaner, brake master cylinder

Hot Tip:

Bleed vehicle twice to ensure all air is removed from system

Performance Gain:

Good brake operation

Complementary Modification:

Replace worn brake parts

When you step on your brake pedal you are compressing a piston in your brake master cylinder. This cylinder is full of brake fluid. The brake fluid that is now under pressure travels through your brake lines and is finally applied to your caliper. It's the calipers' job to squeeze down on the brake pads against the rotor to slow down your car. If the master cylinder cannot create enough pressure to clamp down on the pistons, the brakes will have poor feel. Over time seals get worn in the master cylinder and can leak. In this tech article we will show you how to replace the brake master cylinder in a few easy steps.

Remember your car may have been serviced before and parts replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.

Our vehicle may vary slightly from yours as models do change and evolve as they grow older. If something seems different, let us know and share your info to help other users. Questions or want to add to the article? Leave a comment below.

Disconnect the negative battery terminal. See our tech article on battery replacing.

The brake master cylinder is located below the wiper cowl trim (red arrow) on the left side of the vehicle.
Figure 1

The brake master cylinder is located below the wiper cowl trim (red arrow) on the left side of the vehicle.

Depress the brake pedal half way and hold it in place with a stick or brake pedal depressing tool (red arrow).
Figure 2

Depress the brake pedal half way and hold it in place with a stick or brake pedal depressing tool (red arrow). This will keep fluid in the master cylinder from leaking.

Remove the rubber seal (red arrow) from the cowl.
Figure 3

Remove the rubber seal (red arrow) from the cowl. Lift it at one end and pull it up to remove it.

Next, rotate the plastic retaining tabs (red arrows) 90° to release them.
Figure 4

Next, rotate the plastic retaining tabs (red arrows) 90 degrees to release them.

With all of the tabs released, lift the cowl trim up in the direction of the red arrow and remove it from the cowl.
Figure 5

With all of the tabs released, lift the cowl trim up in the direction of the red arrow and remove it from the cowl.

Pull the wiring harness (red arrow) out of the side of the master cylinder.
Figure 6

Pull the wiring harness (red arrow) out of the side of the master cylinder. Remove the fluid level sensor electrical connector by pressing the locking tab (green arrow) and pulling it off. Remove the brake fluid reservoir cap. Using a fluid extractor, remove all of the fluid from the reservoir. Working at the left lower side of the reservoir, pull the hose (green arrow). This hose feeds hydraulic fluid to the clutch master cylinder. Once detached, plug the hose to prevent debris from entering the hose. (If equipped, you can see my vehicle did not have it.)

Next, the steel lines have to be detached from the master cylinder.
Figure 7

Next, the steel lines have to be detached from the master cylinder. Using a 12mm line wrench, loosen the left side brake line (red arrow).

Using a 12mm line wrench, loosen the top brake line (red arrow).
Figure 8

Using a 12mm line wrench, loosen the top brake line (red arrow).

Pull both brake lines out of the master cylinder (red arrows).
Figure 9

Pull both brake lines out of the master cylinder (red arrows).

Working at the sides of the master cylinder, below the reservoir, remove the right (green arrow) and left side (red arrows) 13mm mounting nuts.
Figure 10

Working at the sides of the master cylinder, below the reservoir, remove the right (green arrow) and left side (red arrows) 13mm mounting nuts. Using a 13mm universal socket on a long extension, remove both brake master cylinder nuts.

Next to the master cylinder, lift it up to remove the plastic support (red arrow).
Figure 11

Next to the master cylinder, lift it up to remove the plastic support (red arrow).

Now the positive battery cable junction has to be removed to make space for the master cylinder to come out.
Figure 12

Now the positive battery cable junction has to be removed to make space for the master cylinder to come out. Start by removing the 13mm bracket nut (red arrow). Then remove the 19mm nut (green arrow). Once the nut is removed, remove the cable from the stud.

Move to the inside of the cowl, remove the 13mm nut from the battery cable (red arrow).
Figure 13

Move to the inside of the cowl, remove the 13mm nut from the battery cable (red arrow).

Pull the front cable with the stud out of the cowl (green arrow).
Figure 14

Pull the front cable with the stud out of the cowl (green arrow). Then move the battery cable (red arrow) aside.

Lift the master cylinder off the brake booster while keeping the lines clear so as not to snag them.
Figure 15

Lift the master cylinder off the brake booster while keeping the lines clear so as not to snag them. You will have to pull it away from the booster to break the vacuum seal of the booster. Pull the master cylinder straight out. Then tilt the reservoir toward the right to get it out of the body.

The next step only has to be performed if your new master cylinder did not come with a reservoir.
Figure 16

The next step only has to be performed if your new master cylinder did not come with a reservoir. Unclip the retaining tab (inset) and hold it, lift the reservoir up to detach it from the master cylinder. Once detached, install in the reverse order of removing to the new master cylinder. You can bench bleed the new master cylinder now. Attach rubber hoses with fittings to the master cylinder and run them into the reservoir. Then press in the piston to bleed the air from the pistons. Install the new master cylinder to the brake booster. Install the nuts finger tight, and leave them loose. Install the brake lines by hand. Be sure not to cross-thread them. The lines should easily thread into the master cylinder. Once the lines are finger tight, tighten the mounting nuts and then the lines. Bleed the brake system and test your brakes before taking the vehicle out for a drive. See our tech article on brake bleeding to help with that portion of the procedure.

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Comments and Suggestions:
Jason Comments: Hi. I have a question. I bled master cylinder and put it back. After I put it back, I could not pump brake pedal. The brake pedal became so hard. I cannot press even 1 mm. It seems that brake is locked. Do you have any suggestion? Thank you in advance.
March 7, 2016
  Followup from the Pelican Staff: Check if the rod is misaligned with the brake master plunger. - Nick at Pelican Parts  

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Page last updated: Mon 12/5/2016 02:42:37 AM