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Brake Booster and ABS Control Unit Replacement on the Porsche 911 Carrera
 
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Pelican Technical Article:

Brake Booster and ABS Control Unit Replacement on the Porsche 911 Carrera

Time:

3 hours3 hrs

Tab:

$250

Talent:

***

Tools:

Brake bleeder, torque wrench

Applicable Models:

Porsche 996 Carrera models (1999-05)
Porsche 996 Turbo, GT2, GT3 (2001-05)
Porsche 997 Carrera models (2005-12)
Porsche 997 Turbo, GT2, GT3 (2007-13)

Parts Required:

Master cylinder, brake fluid

Hot Tip:

Make sure that you keep all brake fluid away from your paint

Performance Gain:

Better braking assist

Complementary Modification:

Replace master cylinder, install stainless steel brake lines

The 911 Carrera is equipped with power brakes that utilize excess vacuum from the engine in order to assist with the pressure needed to apply the brakes. The vacuum is routed from the engine via a long plastic hose that runs up the side of the car, into the front trunk area, and plugs into a large circular brake boost canister that the master cylinder attaches too. After years of use, the rubber diaphragm inside the booster may leak or fail, causing the power assist function to lose its efficiency. In addition, this may cause an engine vacuum leak, which can affect the proper metering of the fuel injection system. Before you replace your brake booster though, be sure that you check the vacuum hose connections that run to the engine to see if there are any leaks there (see Pelican Technical Article: Finding Vacuum Leaks on the Porsche 911 Carrera). Beginning with the introduction of the 997, a mechanical vacuum pump was installed on the engine instead of a conventional air pump for providing the brake booster vacuum. This design enables a high and constant level of vacuum supply.

The first step in removing the booster is to remove the master cylinder (see Pelican Technical Article: Porsche 911 Carrera Master Cylinder Replacement). With the master cylinder removed, disconnect the three fittings from the top ABS control unit that were not attached to the master cylinder. Remove the ABS controller harness plug--the plastic tab on the side slides outward to allow the plug to pull up and off. Pull the brake line pressure regulator out of its clip. Loosen the two nuts on either side of the ABS controller and lift the controller out of the retaining bracket, maneuvering around the existing brake lines.

Now move to the other side of the booster, near the front firewall. Remove the clip that secures the brake booster actuation rod to the brake pedal rod and separate the two (see Figure 2). New boosters have an updated design that includes an integrated boot and an internal screw. This change was put into place for cars manufactured after September 13, 1999, and to use the newer-style booster with the older cars, you need to update the brake push rod and the hardware associated with it. The process of updating the older cars is a bit of a pain, but instructions are documented in a 16-page Porsche Tech Bulletin Boxster 6/01 4770 031 (Brake Booster Seal at the Firewall Changed). See the 101Projects.com website for more information on this update.

With the booster rod disconnected, now disconnect the vacuum line on the front of the booster. Remove the two very long Torx T-45 bolts that secure the brake booster to the firewall. These bolts are the same ones that the master cylinder nuts attach to. With the bolts off, the booster should simply separate from the wall.

Installation of the new booster is basically the reverse of disassembly. With the new brake hardware in place, carefully bleed the brakes according to the instructions found in Pelican Technical Article: Bleeding Porsche 911 Carrera Brakes.

In order to gain access to the linkage that connects the brake pedal to the booster actuator, you need to remove the alarm horn (purple arrow).
Figure 1

In order to gain access to the linkage that connects the brake pedal to the booster actuator, you need to remove the alarm horn (purple arrow). The upper right inset photo shows the vacuum hose plug that connects the engine vacuum line to the booster. Tug on this gently to remove it from the booster housing.

Use a set of wrenches to loosen up the connection between the booster actuator and the pedal cluster rod.
Figure 2

Use a set of wrenches to loosen up the connection between the booster actuator and the pedal cluster rod. This photo shows an early 2000 chassis--later cars have a booster with a longer bellows. The photo in the upper right shows the booster and pedal cluster disconnected. The pedal cluster rod (upper left) must be changed if the booster is replaced with a newer-style one.

This photo shows what needs to be disconnected in order to remove the ABS control unit.
Figure 3

This photo shows what needs to be disconnected in order to remove the ABS control unit. Using a flare-nut wrench, disconnect the main brake lines (yellow arrow). Then release the ABS electrical connection by pulling the connector release handle in the direction of the red arrows. Finally, unbolt the ABS unit from its bracket (purple arrow shows one of the mounting points).

Shown here is the front trunk with the master cylinder and ABS control unit removed.
Figure 4

Shown here is the front trunk with the master cylinder and ABS control unit removed. At this point, the bolts that hold the booster to the firewall have been removed, and the unit is ready to be removed from the car. The photo in the lower right shows the ABS control unit mounting bracket which needs to be removed so that you have enough clearance to pull the booster out (remove nuts--yellow arrows).

Here's the new booster and master cylinder installed.
Figure 5

Here's the new booster and master cylinder installed. At this point, simply remove the protective caps from all of the openings, install the ABS unit, reconnect the vacuum line, and reconnect the brake lines. Don't forget to bleed the entire brake and clutch system (Pelican Technical Article: Bleeding Porsche 911 Carrera Brakes).

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