Brake Master Cylinder: Adjustments

Proper adjustment of the master cylinder pushrod is necessary to ensure proper operation of the power brake system. A pushrod that is too long will prevent the master cylinder piston from completely releasing hydraulic pressure, eventually causing the brakes to drag. A pushrod that is too short will cause excessive brake pedal travel and cause groaning noises to come from the booster when the brakes are applied. A properly adjusted pushrod that remains assembled to the booster with which is was matched during production should not require service adjustment. However, if the booster, master cylinder or pushrod are serviced, the pushrod may require adjustment.

NOTE: Not all boosters are equipped with an adjustable pushrod.

1. Disconnect master cylinder from booster, leaving brake lines connected. Secure cylinder to prevent lines from being damaged.
2. Start engine and operate engine at idle speed.

Fig. 1 Master Cylinder Pushrod Adjustment. Bendix Type Vacuum Booster:

3. With engine running, position gauge over pushrod. Gauge should bottom against booster housing with a force of approximately 5 lb applied to pushrod.
4. If force required to seat gauge exceeds 5 lb, shorten length of pushrod. If force required to seat gauge is less than 5 lb, lengthen pushrod. Ensure pushrod is properly seated in booster when performing gauge inspection.
5. Install master cylinder, then remove reservoir cover.
6. With engine running, observe fluid surface in reservoir when brakes are applied and released rapidly. If no movement is observed on fluid surface, pushrod is adjusted too long.