Parts Catalog Accessories Catalog Tech Info Tech Forums
 
Follow Pelican Parts on Facebook Follow Pelican Parts on Twitter Follow Pelican Parts on Instagram Follow Pelican Parts on YouTube Follow Pelican Parts on Pinterest Follow Pelican Parts on Tumblr
  Search our site:    
View Recent Cars  |   Cart  | Project List | Order Status | Help    
 >  >
Brake Booster Replacing
 
Bookmark and Share

Pelican Technical Article:

Brake Booster Replacing

Nick Czerula

Time:

3 hours3 hrs

Tab:

$300

Talent:

*****

Tools:

11mm line wrenches, 13mm socket, flathead screwdriver

Applicable Models:

BMW Z4 Convertible (2003-06)
BMW Z4 Coupe (2006)

Parts Required:

Brake fluid, brake cleaner, brake booster, brake booster mounting self-locking nuts

Hot Tip:

Bleed vehicle twice to ensure all air is removed from system

Performance Gain:

Good brake operation

Complementary Modification:

Replace master cylinder

Service brakes on the BMW Z4 consist of brake calipers and rotors at the wheels. The calipers are activated hydraulically by the brake master cylinder. A vacuum assisted brake booster multiplies the braking force exerted by the driver at the brake pedal.

When you step on your brake pedal you are compressing a piston in your brake master cylinder and forcing brake fluid under pressure to activate a brake caliper at each wheel. The brake booster is mounted between the brake pedal and the master cylinder. It is supplied with engine vacuum and assists the driver in applying the brakes. The vacuum powering the booster is generated by the engine intake manifold and delivered to the brake booster via a vacuum line with one-way check-valve(s).

The large hollow metal brake booster housing contains a rubber diaphragm. When the brake pedal is applied, an air valve opens allowing atmospheric-pressure air to enter the supply chamber of the brake booster. When this valve opens, the diaphragm moves toward the low pressure (engine vacuum) side. This movement along with the driver input on the brake pedal pushes on the master cylinder piston. When no vacuum is present or the valve does not open, the brake pedal may remain hard and difficult to push.

In some models, the vacuum line check valves leak, allowing engine oil residue to flow to the diaphragm. This causes the diaphragm to fail. The usual symptom of this failure mode is, for example, that your brake pedal requires more effort to keep you stationary at a red light. You may notice the effort needed to keep the brakes applied increases, or the vehicle begins to creep even though pressure on the brake pedal remains steady. If you suspect your brake booster is faulty, this procedure will show you how to replace it.

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 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. When leaving a comment, please leave your vehicle information.

The brake booster is mounted between the brake pedal and the master cylinder.
Figure 1

The brake booster is mounted between the brake pedal and the master cylinder. It is supplied with engine vacuum and assists the driver in applying the brakes. The vacuum powering the booster is generated by the engine intake manifold and delivered to the brake booster via a vacuum line with one-way check-valve(s). The large hollow metal brake booster (red arrow) housing contains a rubber diaphragm. When the brake pedal is applied, an air valve opens allowing atmospheric-pressure air to enter the supply chamber of the brake booster. When this valve opens, the diaphragm moves toward the low pressure (engine vacuum) side. This movement along with the driver input on the brake pedal pushes on the master cylinder piston. When no vacuum is present or the valve does not open, the brake pedal may remain hard and difficult to push.

Start by removing the brake master cylinder (red arrow).
Figure 2

Start by removing the brake master cylinder (red arrow). See our tech article on master cylinder replacing. Then remove the lower dashboard trim panel. See our tech article on lower dashboard trim panel removing

Working at the right side of the brake booster, pull the vacuum supply hose with check valve (red arrow) out of the brake booster.
Figure 3

Working at the right side of the brake booster, pull the vacuum supply hose with check valve (red arrow) out of the brake booster. Be careful not to break or damage the check valve. If you do or suspect it is cracked, replace it. If it is stuck, spray soapy water around valve to help in getting it out.

Working next to the brake pedal underneath the dashboard, remove the brake pedal shaft clip (red arrow).
Figure 4

Working next to the brake pedal underneath the dashboard, remove the brake pedal shaft clip (red arrow). Lever the clip away from the shaft using a flathead screwdriver, then slide the clip off to remove it

The booster push rod can't be removed from the pedal yet, due to the safety bracket (red arrow).
Figure 5

The booster push rod can't be removed from the pedal yet, due to the safety bracket (red arrow). Once the booster is unbolted, it will come off. Using a 13mm universal socket on a long extension, remove the brake booster mounting nuts (blue arrows). The nuts are self-locking. Be sure to replace them with new.

Pull the brake booster (red arrow) out of the firewall and angle it toward the right side of the vehicle.
Figure 6

Pull the brake booster (red arrow) out of the firewall and angle it toward the right side of the vehicle.

Move to the left side of the brake pedal.
Figure 7

Move to the left side of the brake pedal. Gently lever the push rod off the shaft on the brake pedal using a flathead screwdriver (red arrow). As you gently lever, move the road toward the left, and in the engine compartment, the booster toward the right. This will detach the push rod and allow enough room for it to fit out from inside the safety bracket.

Slide the push rod straight out once free.
Figure 8

Slide the push rod straight out once free.

Working inside the engine compartment, remove the brake booster from the vehicle by lifting it straight up and pulling it out.
Figure 9

Working inside the engine compartment, remove the brake booster from the vehicle by lifting it straight up and pulling it out. If reinstalling or dealing with a water leak, replace the brake booster seal. Install the new brake booster in the reverse order of removal. Feed the booster into the firewall, but do not insert the studs into the holes yet. Align the booster to the brake pedal connection. Hold it in place while installing the push rod and clip. Then tighten the booster mounting nuts and install the master cylinder and remaining parts. Bleed the brakes. Check the operation of the brakes and confirm that the booster functions normally.

Bookmark and Share

  Search our site:    

View Cart & CheckOut | Project List | Order Status |  Help    

 

[Home] [Customer Service] [Shopping Cart] [Privacy Statement]
 [Contact Us] [About Us] [Shipping] [Map to our Location] [Careers]

Copyright © Pelican Parts Inc.

Page last updated: Sat 12/3/2016 03:07:32 AM