ParkAvenue 1997-1999

Power Brake Booster

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Specific to:

Buick LeSabre 1986-1999

Buick Park Avenue 1996-1999

Oldsmobile 88 1992-1999

Oldsmobile Delta 88 1986-1988

Oldsmobile LSS 1996-1999

Pontiac Bonneville 1987-1999

Virtually all modern vehicles use a vacuum assisted power brake system to multiply the braking force and reduce pedal effort. Since vacuum is always available when the engine is operating, the system is simple and efficient. A vacuum diaphragm is located on the front of the master cylinder and assists the driver in applying the brakes, reducing both the effort and travel he must put into moving the brake pedal.

The vacuum diaphragm housing is normally connected to the intake manifold by a vacuum hose. A check valve is placed at the point where the hose enters the diaphragm housing, so that during periods of low manifold vacuum brakes assist will not be lost.

Depressing the brake pedal closes off the vacuum source and allows atmospheric pressure to enter on one side of the diaphragm. This causes the master cylinder pistons to move and apply the brakes. When the brake pedal is released, vacuum is applied to both sides of the diaphragm and springs return the diaphragm and master cylinder pistons to the released position.

If the vacuum supply fails, the brake pedal rod will contact the end of the master cylinder actuator rod and the system will apply the brakes without any power assistance. The driver will notice that much higher pedal effort is needed to stop the car and that the pedal feels harder than usual.

Removal & Installation



Specific to:

Buick LeSabre 1986-1990

Buick Park Avenue 1996-1999

Oldsmobile Delta 88 1986-1988

Pontiac Bonneville 1987-1990

  1. Unfasten the retaining nuts, then remove the master cylinder from the booster. It is not necessary to disconnect the lines from the master cylinder. Just move the cylinder aside for access to the power booster. Be careful not to flex or distort the brake lines.
  2.  
  3. Disconnect the vacuum booster pushrod from the brake pedal inside the car. It is retained by a bolt. A spring washer lies under the bolt head, and a flat washer goes on the other side of the pushrod eye, next to the pedal arm.
  4.  
  5. Remove the four attaching nuts from inside the vehicle, then remove the booster from its mounting position on the firewall.
  6.  



Click image to see an enlarged view

Fig. Exploded view of the power booster mounting

To install:

  1. Position the booster on the firewall. Tighten the mounting nuts to 15 ft. lbs. (21 Nm).
  2.  
  3. Connect the booster pushrod to the brake pedal.
  4.  
  5. Install the master cylinder and secure with the retaining nuts. Tighten the nuts to 20 ft. lbs. (27 Nm).
  6.  

Specific to:

Buick LeSabre 1991-1999

Buick Park Avenue 1996-1999

Oldsmobile 88 1992-1999

Oldsmobile LSS 1996-1999

Pontiac Bonneville 1991-1999


WARNING
For 1994-99 vehicles with ABS, after bleeding the brake system you must perform an "Auto Bleed" sequence, using a Tech 1® or equivalent scan tool. If you do not have access to a suitable scan tool, your vehicle will probably have to be towed to a shop with the proper diagnostic equipment to have the procedure performed.

The booster can be removed from the vehicle without removing or disconnecting the master cylinder. However, if both the booster and master cylinder are to be removed, remove the master cylinder first.

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the booster vacuum hose from the vacuum check valve.
  4.  



Click image to see an enlarged view

Fig. Disconnect the power booster vacuum hose from the vacuum check valve

  1. Unfasten the master cylinder attaching nuts. Separate the master cylinder from the booster. Move the master cylinder forward just enough to clear the booster studs. This will flex the brake pipes slightly, so be very careful not to bend or distort the pipes.
  2.  
  3. Remove the acoustical barrier from the booster studs, located inside the passenger compartment, under the instrument panel.
  4.  
  5. Unfasten the booster attaching nuts, from inside the vehicle.
  6.  
  7. Remove the booster from the brake pedal. Tilt the entire booster slightly to work the pushrod off the pedal clevis pin without putting undue side pressure on the pushrod.
  8.  
  9. Remove the booster from the vehicle, then remove the gasket.
  10.  



Click image to see an enlarged view

Fig. Exploded view of the brake power booster mounting - 1991-99 vehicles

To install:

  1. Place the gasket on the booster. Position the booster in the vehicle.
  2.  
  3. Attach the booster pushrod to the brake pedal. Tilt the entire booster slightly to work the pushrod onto the pedal clevis pin without putting undue side pressure on the pushrod.
  4.  
  5. Install the booster attaching nuts and tighten to 15 ft. lbs. (21 Nm).
  6.  
  7. Install the acoustical barrier to the booster studs, located under the instrument panel.
  8.  
  9. Position the master cylinder to the booster and secure with the retaining nuts. Tighten the nuts to 20 ft. lbs. (27 Nm).
  10.  
  11. Attach the booster vacuum hose to the vacuum check valve.
  12.  
  13. Connect the negative battery cable.
  14.  

Testing



System Operation Test

Specific to:

Buick LeSabre 1986-1999

Buick Park Avenue 1996-1999

Oldsmobile 88 1992-1999

Oldsmobile Delta 88 1986-1988

Oldsmobile LSS 1996-1999

Pontiac Bonneville 1987-1999

  1. With the engine OFF , pump the brake pedal until the supply vacuum is entirely gone.
  2.  
  3. Put light, steady pressure on the brake pedal.
  4.  
  5. Start the engine and let it idle. If the system is operating correctly, the brake pedal should fall toward the floor if the constant pressure is maintained.
  6.  

Power brake systems may be tested for hydraulic leaks just as ordinary systems are tested.

Vacuum Leak Test

Specific to:

Buick LeSabre 1986-1999

Buick Park Avenue 1996-1999

Oldsmobile 88 1992-1999

Oldsmobile Delta 88 1986-1988

Oldsmobile LSS 1996-1999

Pontiac Bonneville 1987-1999

  1. Operate the engine at idle without touching the brake pedal for at least one minute.
  2.  
  3. Turn off the engine and wait one minute.
  4.  
  5. Test for the presence of assist vacuum by depressing the brake pedal and releasing it several times. If vacuum is present in the system, light application will produce less and less pedal travel. If there is no vacuum, air is leaking into the system.
  6.  

 
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