Vacuum Brake Booster: Adjustments

DESCRIPTION
The power brake booster has an adjustable push rod (output rod) which is used to compensate for dimensional variations in an assembled power brake booster. The push rod length is adjusted after it has been assembled in production. A properly adjusted push rod that remains within the power brake booster after it was assembled in production should never require a service adjustment.

TESTING
A power brake booster that is suspected of having an improper push rod length will indicate either of the following:
^ A push rod which is too long will prevent the brake master cylinder piston from completely releasing hydraulic pressure causing brakes to drag.
^ A push rod which is too short will increase brake pedal travel causing a clunking or groaning noise from the power brake booster.





PUSH ROD ADJUSTMENT
If necessary, a booster push rod length can be verified with a push rod gauge using the following procedure:
^ Without disconnecting the brake tubes, disconnect the brake master cylinder and set it away from the booster power unit. The brake master cylinder must be supported to prevent damaging the brake tubes.
^ With the engine idling, gauge and adjust the push rod length. A force of approximately 22 N (5 lb) applied to the push rod with the gauge will make sure that the push rod is seated with the power brake booster.
^ Install the brake master cylinder on the power brake booster. Gradually alternate the tightening of the retaining nuts to 21-29 Nm (16-21 ft. lbs.).