Brake Booster Replacement

  • Materials Required

    • BMW OBD2 Scan Tool
    • 10MM Socket
    • 10MM Wrench
    • Ratchet w/ Extension
    • Flathead Screwdriver
    • 2L DOT-4 Brake Fluid
    • Hand Pump or Turkey Baster
    • Paper Towels
  • NOTE*

    The brake booster fails over time for many reasons, the most common being a tear in the rubber diaphragm that causes braking issues. When the brake booster fails, the brake pedal will lock up and be completely stiff or the brakes will not engage at all.

  • Open Hood

    Open your vehicle's hood by pulling the latch.

  • Remove Cabin Air Filter Cowl

    Remove the cabin air filter, HVAC cowl and all covers in the way of accessing the brake booster. You should only need an 8MM socket for this.

  • Remove Driver Footwell Panel

    Remove the driver-side footwell panel by removing the three T-20 retention screws.

  • Remove Brake Pedal Clip

    Unscrew the fuel rail vent cap and place it off to the side. No tools are required for this.

  • Unseat Brake Pedal Pin

    Unseat the brake pedal pin by using a hammer to lightly tap it out of place.

  • Loosen Torque

    To fully free the brake pedal pin from the brake assembly, loosen the torque from the brake booster so the pin is free to be removed. Do not remove brake booster nuts fully yet.

  • Remove Brake Pedal Pin

    Finish removing the brake pedal retention pin by sliding it towards the passenger side and wiggling it from the brake pedal.

  • Remove Brake Booster Nuts

    With the brake booster nuts already loosened, remove them completely out of place now.

  • Remove Booster Knuckle

    With the brake booster nuts completely removesd, wiggle the knuckle (white arrow) off of the brake pedal assembly.

  • Unplug Brake Reservoir Connector

    Unplug the brake reservoir connector by depressing the retention tab and pulling it back.

  • Drain Brake Fluid

    Drain as much brake fluid as possible from the brake fluid reservoir, to avoid spillage in the later steps.

  • Unplug ABS Module Connector

    Unplug the main electrical connector to the DSC module by pulling upwards on the retention clip and wiggling it off.

  • Loosen Fluid Lines

    Loosen the six 11MM brake fluid lines (white arrows) that attach to the top of the DSC module and disconnect them. You do not need to remove them completely from the vehicle, just remove the DSC connecting point.

  • Loosen Fluid Lines Cont.

    Loosen and disconnect the two 11MM brake fluid lines that connect to the master cylinder down below (white arrows).

  • Remove Master Cylinder Fluid Lines

    You do not need to remove any of the fluid lines except the two that connect to the master cylinder.

  • NOTE*

    When disconnecting the bottom brake fluid lines from the master cylinder, brake fluid will leak down the drain port at the driver-side wheel. Put some paper towels into place to avoid chemical stains.

  • Remove DSC Module Nuts

    Remove the three 10MM nuts holding the DSC module in place (white arrows).

  • NOTE*

    It's highly recommended to use a retractable magnet to extract the DSC module nuts. The nuts are fastened in an awkward location and are very easy to drop otherwise.

  • Remove DSC Module

    Remove the DSC module from the engine bay ensuring not to damage any of the brake lines.

  • Disconnect Booster Vacuum Line

    Disconnect the brake booster vacuum line pictured by depressing the white retention clip downwards (white arrow), while pulling the male end backwards towards the red arrow.

  • Disconnect Master Cylinder

    Disconnect the master cylinder by removing the two 10MM retention nuts that hold it to the brake booster.

  • Remove Master Cylinder

    With the two nuts removed, the master cylinder can be pulled off of the brake booster.

  • Remove Brake Booster

    To remove the brake booster, simply grab it and wiggle it free of all fluid lines. You may need to rotate it around to free up space to pull it from the engine bay.

  • NOTE*

    When installing the new brake booster, replace the check valve seal with a brand new one. This will minimize the risk of a vacuum leak in the future.

    Part No. 34336893085

  • NOTE*

    When installing the new brake booster, also replace the check valve and vacuum line that connects directly to the booster. This will minimize the risk of a vacuum leak in the future.

    Part No. 34337577336

  • Install Booster Vacuum Line

    Install the brake booster check valve and vacuum line to the booster and orient it as shown. It's significantly easier to install this hose to the booster when it's out of the vehicle.

  • Seat New Brake Booster

    Seat the brake booster back into place, but do not install it fully flush. You will need the booster loose to move around that way you an install the master cylinder to it.

  • Reinstall Master Cylinder

    Reinstall the master cylinder by fixing the two 10MM retention nuts back onto the booster.

  • Reinstall DSC Module

    Reinstall the DSC module back into engine bay.

  • NOTE*

    Hand-thread the brake fluid lines back onto the DSC module before torquing them down with a wrench. Hand-threading them first will ensure they don't get cross-threaded. Once fully hand-threaded, you an tighten them down with a 10MM wrench.

  • Reinstall Master Cylinder Fluid Lines

    Reinstall the lower brake fluid line that connects to the master cylinder. Ensure you tighten down the end that connects to the cylinder itself also.

  • Seat Brake Booster Knuckle

    Seat the silver brake booster knuckle back onto the brake pedal. You may have to move the brake pedal back and forth to get the holes to align.

  • Reinstall Brake Pedal Pin

    Reinstall the metal brake pedal pin (white arrow) so it feeds all of the way through the pedal and brake booster knuckle.

  • NOTE*

    The brake pin must by installed through the brake pedal from right to left. The slit on the metal pin should be facing closest to the driver side.

  • Install New Brake Pedal Clip

    Install a new brake pedal retention clip by sliding it over the metal pin. This part must be replaced with a new one, do not re-use your old one.

    Part No. 07129904567

  • Install 10MM Nuts

    Reinstall the two 10MM nuts that secure the brake booster and torque them down tightly.

  • NOTE*

    After replacing the brake booster, you may have trouble starting the vehicle. This is because the brake sensor needs to be reset. To reset the brake sensor, press the brake pedal all of the way down in the direction of the red arrow, then while holding it down, press the two retention tabs on the brake sensor (white arrow) and push the sensor all of the way down. After the sensor is pushed all of the way down, let go of it then let go of the brake pedal. The brake pedal should press against the sensor and reset it to the factory position. Press here and fast-forward to 15:29 for a visual.

  • Fill Brake Fluid Reservoir

    Refill the brake fluid reservoir with approved full synthetic DOT-4 brake fluid.

  • Bleed Brake System

    You absolutely must bleed the brake system after replacing the brake booster, before driving the vehicle. Failure to do this will result in loss of brakes and the vehicle will not be able to stop. Press here to learn how to bleed air out of the brake system.


    Again, bleed the brakes before trying to start the vehicle. You will have zero braking power as soon as you turn the vehicle on if not.

  • Re-Installation

    Re-install all components in the vice versa of removal. i.e cabin air filter and cowl, covers, etc.

  • Clear Engine Codes

    Using a BMW scan tool, clear all engine codes that may be present.

  • Test Start Car

    Test start the car to ensure the new brake booster works properly and isn't faulty. You may have to press down on the brake pedal very hard the first few times.

  • *NOTE*

    As you test start the car, have a friend check your brake calipers to ensure the brakes are activating when you press the brake pedal. Leave the car running and check for any brake fluid leaks that may be present. Once you've confirmed no issues are present, you may shift the car out of park and take it out on a test drive.

  • DIY Complete!

    Good job replacing your brake booster and bleeding your brake system! Be sure to keep an eye on your dashboard for any check engine codes and pay attention to any issues you're having regarding brake feel.