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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 socket, T25 Torx bit socket

Applicable Models:

BMW Z3 (1996-02)

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

BMW Z3 service brakes consist of hydraulic brake calipers and rotors, one at each wheel. When the brake pedal is pressed, brake fluid is forced out of the brake master cylinder and through the brake lines to each brake caliper. Pistons in the calipers push out and clamp brake pads against the brake rotors (or discs), thus slowing down the vehicle. A vacuum assisted brake booster multiplies the braking force exerted by the driver at the brake pedal.

If the brake master cylinder cannot create enough pressure to clamp the brake pads firmly against the brake rotors, the brakes will have a 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. 

Keep in mind that when your car was serviced before, parts may have been 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 you're 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. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

Make sure to clean around the cap before removing it, as you do not want to get any dirt into the reservoir.
Figure 1

Make sure to clean around the cap before removing it, as you do not want to get any dirt into the reservoir. Remove the brake reservoir cap, then using a fluid extractor, remove all of the fluid from the reservoir.

Reinstall the cap to prevent debris from entering reservoir.
Figure 2

Reinstall the cap to prevent debris from entering reservoir. Then remove fluid level sensor electrical connector by releasing locking tab (green arrow) and pulling off.

Be sure the vehicle key is OFF for at least 15 minutes.
Figure 3

Be sure the vehicle key is OFF for at least 15 minutes. Then disconnect the three electrical connector junctions (green arrows) at master cylinder by unscrewing them counterclockwise.

Pull wire out of mounts to access connector junction release tabs.
Figure 4

Pull wire out of mounts to access connector junction release tabs. You can leave the zip tie (green arrow) in place.

Using a small flathead screwdriver, release connector junction release tabs (green arrows) by levering them toward master cylinder.
Figure 5

Using a small flathead screwdriver, release connector junction release tabs (green arrows) by levering them toward master cylinder. Pull up on junction to detach it from fuse panel while holding tabs in the released position. Lift junction up and move it toward the front of the vehicle to gain access to the rear brake line.

Using an 11mm line wrench, loosen the rear brake line (green arrow).
Figure 6

Using an 11mm line wrench, loosen the rear brake line (green arrow).

Using a 12mm line wrench, loosen the front brake line (green arrow).
Figure 7

Using a 12mm line wrench, loosen the front brake line (green arrow).

Using a 13mm socket on an extension, remove both brake master cylinder nuts (green arrows).
Figure 8

Using a 13mm socket on an extension, remove both brake master cylinder nuts (green arrows).

Once you remove the nuts, lift the master cylinder off the brake booster while pulling the lines out of the threaded bores.
Figure 9

Once you remove the nuts, lift the master cylinder off the brake booster while pulling the lines out of the threaded bores. You will have to pull it away from the booster to break the vacuum seal of the booster.

The next few steps only have to be performed if your new master cylinder did not come with a reservoir.
Figure 10

The next few steps only have to be performed if your new master cylinder did not come with a reservoir. Using a T25 Torx bit socket, remove the brake fluid reservoir mounting bolt (green arrow).

Now you can lift the reservoir up to detach it from the master cylinder.
Figure 11

Now you can 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. Install the new master cylinder to the brake booster, install the nuts finger tight, leave them loose. Install brake lines by hand, be sure not to cross-thread them. The lines should easily thread into the new 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:
Bergy Comments: Is there any need to prime or 'bench bleed' the master cylinder before installing? I didn't see that anywhere in this or the brake bleeding tech article.
August 22, 2016
  Followup from the Pelican Staff: Most times the master cylinder will come with a kit and instructions for bench bleeding. However, the process can be done with it installed as well, by leaving the lines loose, gravity bleeding, then bleeding via the line connections first. - Nick at Pelican Parts  
morrie Comments: There is nothing in the article about replacing an o-ring or the nuts that come with the master cylinder. Are these 2 items necessary parts when replacing the MC??
January 13, 2016
  Followup from the Pelican Staff: The O-ring comes with the new master cylinder, usually pre-installed. The nuts can be replaced if they are self-locking. - Nick at Pelican Parts  

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Page last updated: Sat 12/3/2016 02:08:15 AM