Brake Booster-to-Master Cylinder Push Rod

Some vacuum boosters have an adjustable push rod (output rod) which is used to compensate for dimensional variations in an assembled booster. The push rod length is adjusted after each booster power unit has been assembled in production. A properly adjusted push rod that remains assembled to the booster with which it was matched in production should never require a service adjustment.

A booster that is suspected of having an improper push rod length will indicate either of the following:

• A push rod that is too long will prevent the master cylinder piston from completely releasing hydraulic pressure, eventually causing the brakes to drag.
• A push rod that is too short will increase brake pedal travel and cause a groaning noise from the booster.

NOTE: A locally made push rod gauge of the following dimensions must be used.

If necessary, a booster push rod length can be verified with a push rod gauge by using the following procedure:

1. Without disconnecting the brake tubes, disconnect the master cylinder, and position it away from the booster power unit. The master cylinder must be supported to prevent damaging the brake tubes.

    CAUTION: Do not adjust too long or brake drag could result.

2. With the engine running, gauge and adjust the push rod length. A force of approximately 22 N (5 lb) applied to the push rod with the gauge will ensure that the push rod is seated within the power unit.
   
   
   
   

3. Install the master cylinder on the power unit. Gradually and alternately tighten the retaining nuts to 21-29 Nm (16-21 lb-ft). Refer to Section 06-00.