The vacuum booster system uses a tandem vacuum suspended unit. In a normal operating mode, with the service brakes in the released position, the vacuum booster operates with vacuum on both sides of its diaphragms. When the brakes are applied, air at atmospheric pressure is admitted to one side of each diaphragm to provide the power assist. When the brakes are released, the atmospheric air is shut off from one side of each diaphragm. The air is then drawn from the booster through the vacuum check valve to the vacuum source.
The internal components of this booster are not serviceable. If the booster is proved defective, it must be replaced as a unit.
Removal & Installation
At one time, vacuum boosters simply bolted to the cowl (firewall) and were easily serviced. These vehicles, however, use a twist-lock (sometimes called a cam-lock) type of mounting system. A special tool is used that bolts to the master cylinder mounting studs and a large wrench is used to twist the booster to disengage/engage the locking tabs. Use care if using substitute tools.
- On 3.8L engines, remove the cosmetic/acoustic engine cover.
- On 3.4L (VIN X) engines, remove the throttle body and tube, using the procedures found in Section 5.
- Unbolt the ABS hydraulic modulator/master cylinder assembly from the booster, as outlined under the ABS portion of this section. On some vehicles, it might not be necessary to disconnect any hydraulic lines. Some brake line clips and retainers may have to be removed and/or disengaged to allow some working room. Use care not to bend and crimp any brake lines. Move the assembly just enough to disengage the master cylinder from the two studs on the front of the booster.
- Disconnect the transaxle filler tube and remove, if necessary.
- On 3.8L engines, remove the EGR heat shield.
- Disconnect the vacuum hose from the brake booster.
- Disconnect the brake pedal pushrod from the brake pedal. It is retained by a sheetmetal clip. Carefully lift the tab that covers the brake pedal pivot and slide the clips from the brake pushrod. Use care not to distort the clip as it will be needed for installation.
Unlock the booster from the front of the cowl (firewall) as follows:
- Attach booster holding tool J 22805-01, or equivalent, to the master cylinder mounting studs with the nuts. Tighten the stud nuts to 20 ft. lbs. (27 Nm).
- Use a suitable prybar to pry the locking tab on the booster out of the locking notch on the mounting flange.
- At the same time, turn the booster counterclockwise with a large wrench on the booster holding tool.
- Remove the brake booster from the vehicle. Be careful not to damage the insulator boot mounted on the front of the dash when pulling the pushrod end through the hole.
- Lightly lubricate the inside and outside diameters of the grommet and front housing seal with silicone grease before installation.
- Attach tool J 22805-01, or equivalent, to the booster with the nuts. Tighten the nuts to 20 ft. lbs. (27 Nm).
- Position the booster on the cowl, slightly counterclockwise from the final installation position, so that the locking flanges on the booster and mounted plate engage.
- Connect the booster pushrod to the brake pedal. Verify that the retainer clip is properly engaged on the brake pedal pivot pin and that the top of the clip covers the end of the pin.
- Turn the booster clockwise with a wrench on tool J 22805-01, until the locking flanges are engaged. Make sure the locking tab is fully seated to prevent rotation of the booster. It is not necessary to use a prytool on the locking tab to install the booster. When correctly installed, the locking tab will slide up the flange and snap in the locking notch.
- Install the ABS hydraulic modulator/master cylinder assembly.
- Depending on the vehicle model and engine assembly, install the remaining components.
- Connect the negative battery cable and bleed the system if the fluid pipes were disconnected from the master cylinder.