Power brake booster — check, removal and installation
Operating check
1. Depress the brake pedal several times with the engine off and make sure there’s no change in the pedal reserve distance.
2. The booster reserve vacuum should be entirely used at this point.
3. While still holding the pedal down firmly, start the engine. The pedal should continue to fall to the floor. Let up on the pedal, (engine still running) wait a few seconds and apply the brake pedal again. The pedal should return to its normal position.
4. If the pedal does not return to the normal position the booster is not working correctly. Check the vacuum to the booster. If the vacuum is good, the booster is faulty. Replace the booster.
Airtightness check
5. Start the engine and turn it off after one or two minutes. Depress the brake pedal slowly several times. If the pedal depresses less each time, the booster is airtight.
6. Depress the brake pedal while the engine is running, then stop the engine with the pedal depressed. If there’s no change in the pedal reserve travel after holding the pedal for 30 seconds, the booster is airtight.
Removal
Note: With the engine off, pump the brake pedal several times to deplete the vacuum in the power brake booster.
7. Power brake booster units shouldn’t be disassembled. They require special tools not normally found in most automotive repair stations or shops. Because of its critical relationship to brake performance, the booster should be replaced with a new or rebuilt one.
8. Disconnect the cable from the negative terminal of the battery (see Engine electrical systems), then remove the windshield wiper motor (see Chassis electrical system) and cowl/cowl reinforcement (see Body). Remove the brake master cylinder (see Master cylinder — removal, installation and reservoir/grommet replacement).
9. Disconnect the hose leading from the engine to the booster. Be careful not to damage the hose when removing it from the booster fitting.
10. Remove the driver’s knee bolster/airbag (see Body).
11. Remove the ABS actuator assembly (see Anti-lock Brake System (ABS) and Vehicle Stability Control (VSC) -general information, trouble codes and component removal and installation).
12. Remove the pedal return spring. Locate the pushrod clevis connecting the booster to the brake pedal. Remove the clevis pin retaining clip with pliers and pull out the pin.
13. Remove the four nuts holding the brake booster to the firewall (see illustrations); you may need a light to see them.
i. 13a Left side booster retaining nuts
i. 13b Right side booster retaining nuts
14. Slide the booster away from the firewall until the studs clear the holes, then remove it.
Installation
15. Installation procedures are basically the reverse of removal. Tighten the clevis locknut securely and the booster mounting nuts to the torque listed in this Chapter’s Specifications.
16. If a new power brake booster unit is being installed, check the pushrod clearance (see illustration) as follows:
- Measure the distance that the pushrod is recessed from the master cylinder mounting surface on the front of the power brake booster. Record this measurement.
- This is «dimension A. «
- Measure the distance from the mounting flange to the end of the master cylinder.
- Record this measurement. This is «dimension B.»
- Measure the distance from the end of the master cylinder to the bottom of the pocket in the piston.
- Record this measurement. This is «dimension C.»
- Subtract measurement B from measurement C, then subtract measurement A from the difference between B and C. This is the pushrod clearance.
- Compare your calculated pushrod clearance to the pushrod clearance listed in this Chapter’s Specifications. If necessary, adjust the pushrod length to achieve the correct clearance.
i. 16 There should be no clearance between the booster pushrod and the master cylinder pushrod, but no interference either. If
there is interference between the two, the brakes may drag; if there is clearance, there will be excessive brake pedal travel
17. After the final installation of the master cylinder and brake hoses and lines, the brake pedal height and free play must be adjusted and the system must be bled. See the appropriate Sections of this Chapter for the procedures.