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Brake Booster Replacement
 
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Pelican Technical Article:

Brake Booster Replacement

Nick Czerula

Time:

3 hours3 hrs

Tab:

$300

Talent:

*****

Tools:

11mm, 12mm line wrenches, 13mm socket, floor jack, jack stands, wheel chocks, safety glasses, lug wrench, torque wrench

Applicable Models:

BMW 525i/xi Sedan (2004-07)
BMW 528i xDrive Sedan (2009-10)
BMW 528i/xi Sedan (2008-10)
BMW 530i/xi Sedan (2004-07)
BMW 530xi Wagon (2006-07)
BMW 535i xDrive Sedan/Wagon (2009-10)
BMW 535i/xi Sedan (2008-10)
BMW 535xi Wagon (2008)
BMW 545i Sedan (2004-05)
BMW 550i Sedan (2006-10)
BMW M5 Sedan (2006-10)

Parts Required:

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

Hot Tip:

Bleed brakes twice to ensure all air is removed from system

Performance Gain:

Good brake operation

Complementary Modification:

Replace master cylinder

In addition to replacing and bleeding the brake fluid, servicing brakes on the BMW E60 consists of replacing the brake pads, brake calipers and rotors at the wheels. The brake master cylinder activates the calipers hydraulically. 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 a supplemental vacuum pump and delivered to the brake booster via a 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. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

Start by removing the brake master cylinder.
Figure 1

Start by removing the brake master cylinder. 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 2

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 to be cracked, replace it. If it is stuck, spray soapy water around the valve to help in getting it out.

Working next to the brake pedal (green arrow) underneath the dashboard, remove the brake pedal shaft clip (red arrow).
Figure 3

Working next to the brake pedal (green arrow) underneath the dashboard, remove the brake pedal shaft clip (red arrow). See the following steps for details on removing the clip.

Lever the clip away from the shaft in the direction of the red arrow.
Figure 4

Lever the clip away from the shaft in the direction of the red arrow. Then slide the clip down to remove it, in the direction of the green arrow.

Move to the right side of the brake pedal.
Figure 5

Move to the right side of the brake pedal. Swing the mounting pin lock (red arrow) up to disconnect it from the brake booster shaft and slide it out of the brake pedal / brake booster junction in the direction of the green arrow.

Using a 13mm universal socket on a long extension, remove the brake booster mounting nuts (red arrows).
Figure 6

Using a 13mm universal socket on a long extension, remove the brake booster mounting nuts (red arrows). The nuts are self-locking. Be sure to replace them with new ones.

Working inside the engine compartment, remove the brake booster from the vehicle by lifting it straight up and pulling it out.
Figure 7

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 (red arrow).
Figure 8

If reinstalling or dealing with a water leak, replace the brake booster seal (red arrow).

Install the new brake booster in the reverse order of removal.
Figure 9

Install the new brake booster in the reverse order of removal. Once the booster is installed in the body, install the nuts finger tight. Then align the booster to the brake pedal connection. Hold it in place while installing the connection pin and clip. Then tighten the booster mounting nuts and install the master cylinder and remaining parts. Bleed the brakes. See our tech article on brake bleeding. Check the operation of the brakes and confirm that the booster functions normally.

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Comments and Suggestions:
Doug Comments: I assume you have to bleed the brake system once you replace the brake booster correct? I thought my brake rotors are too thin causing my car to loose braking effectiveness. After installing new rotors, issue is still there. I would apply the brake and car would still coast. Only come to a complete stop after I press the brake pedal all the way down hard. Scary feeling...
September 12, 2015
  Followup from the Pelican Staff: Sounds like a bad brake booster. Check if it is full of oil, if so, replace the vacuum pump as well.
You will have to bleed your brakes.- Nick at Pelican Parts
 
ricky Comments: I replaced my brake booster and now the DBC light comes on after 5 min of driving. Could air in the system cause this error!
September 6, 2015
  Followup from the Pelican Staff: It could be. i would start by checking the vehicle for fault codes. If the brake pedal is soft, do not drive the vehicle. - Nick at Pelican Parts  
nick Comments: Great article, thanks. My breaks are failing after a few pump of the brakes. It then takes 5 seconds to start working again. It's obviously leaking somewhere, do you have any advice? I'm keen to try and fix it myself...but quite wary of doing something wrong!
Thanks
August 3, 2015
  Followup from the Pelican Staff: Look for a fluid leak, top up the fluid. Then pump the brakes with the engine off. Listen for a light squirting sound or signs of a fluid leak. - Nick at Pelican Parts  
Chris Comments: Vacuum is providing 27mmHg of vacuum. As soon as I turn the car off the vacuum dissipates pretty rapidly. I can hear a hissing noise somewhere around the booster, but definitely not through the grommet to the check valve. I don't hear any hissing during running, although it could be masked by engine noise. Thanks!
April 15, 2015
  Followup from the Pelican Staff: I would idle the engine with the vacuum connection at the booster removed and sealed. Then check if the leaking sound is still present if not,t he issue is likely the booster. - Nick at Pelican Parts  
Chris Comments: I thought I had a bad master cylinder so I replaced it, but my brake issues remain. I am getting boost assistance, but I don't get any real braking power until the last 5% of the brake pedal travel. Also, when the car is off, I can push the brake pedal down to the floor fairly easily. Would these be symptoms of a failed or leaking booster?
April 14, 2015
  Followup from the Pelican Staff: I would check for good vacuum to the booster, if it is sufficient. The booster may be at fault. they are common failures on E60 models. - Nick at Pelican Parts  

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Page last updated: Sat 12/3/2016 02:42:38 AM