How to Fix a Brake Power Booster

Brake booster located to the right of engine

Power brakes utilize vacuum generated by the engine to lessen the force needed to apply the brakes in a vehicle as well as shorten the distance the brake pedal needs to travel. The power brake booster acts as a diaphragm that controls the level of vacuum or boost applied to the master cylinder.

Things You'll Need

• Socket set
• Wrench set
• Phillips screwdriver
• Flat-blade screwdriver
• Pliers

Instructions

Removal

1. Disconnect the ground cable from the negative battery terminal by loosening the retaining bolt and pulling the clamp off the terminal.

2. Locate the power brake booster. It will be mounter on the driver's side of the firewall behind the master cylinder.

3. Loosen but do not remove the bolts that connect the master cylinder to the power brake booster.

4. Gain access to the nuts and bolts that secure the power brake booster to the firewall. Depending on the design of your vehicle, you may have to remove the trim panel located just below the steering column.

5. Disconnect the brake booster pushrod from the brake pedal, depending on the vehicle it may be bolted or held with a clip.

6. Disconnect the electrical connector for the stoplight switch.

7. Disconnect the vacuum hose from the power brake booster.

8. Remove the nuts and bolts that connect the brake booster to the firewall.

9. Remove the bolts that connect the master cylinder to the brake booster.

10. Separate the brake booster from the master cylinder. Be careful not to damage the brake lines attached to the master cylinder.

11. Remove the brake booster from the vehicle.

Installation

1. Set the new power brake booster into position on the firewall.

2. Reinstall the bolts and nuts that secure it to the firewall.

3. Reconnect the booster pushrod to the brake pedal.

4. Reconnect the electrical connector to the brake light switch.

5. Reconnect the vacuum line to the brake booster.

6. Reconnect the master cylinder to the power brake booster and reinstall the bolts that connect them.

7. Check the fluid level in the master cylinder and fill if needed.

8. Reconnect the ground cable to the negative battery terminal.

Tips & Warnings

• Do not remove the brake lines from the master cylinder. Doing so will allow air into the system, and you will have to bleed the brakes to get them functioning properly.

• Brake fluid can strip paint. Do not allow brake fluid to come in contact with any painted surface on your vehicle.

References

• Chilton's Wrangler/YJ 1987-1994 Repair Manual; Chilton Book Company; 1995
• Chilton Mazda 1978-1989 Repair Manual; Haynes North America; 1995
• Haynes Chevrolet & GMC Full-size Vans 1968 through 1996 Repair Manual; Don Pfeil and John H. Haynes; 1999

Resources

• Popular Mechanics