Calais FWD L4-151 2.5L (1985)
Vacuum Brake Booster: Adjustments
Pushrod Adjustment
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
cause the master cylinder piston to close off the compensating port, preventing hydraulic pressure from being released and resulting in brake 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 it was matched during production should not require service adjustment.
However, if the booster, master cylinder or pushrod are serviced, the pushrod may require adjustment.
There are two methods that can be used to check for proper pushrod length and installation: the gauge method and air method. Usually, if the power
unit pushrod requires an adjustment the Power Unit Repair Kit for the unit being serviced includes a gauge. The gauge measures from the end of the
pushrod to the power unit shell.
GAUGE METHOD
Fig. 1 Master cylinder pushrod adjustment. Bendix type vacuum booster
Bendix Type
1.
Disconnect master cylinder from booster leaving brake lines connected, and secure cylinder to prevent lines from being damaged.
2.
Start engine and allow to run at normal curb idle speed.
3.
With engine running, position gauge over pushrod. Gauge should and bottom against booster housing with a force of approximately 5 lbs. applied
to pushrod, Fig. 1.
4.
If force required to seat gauge exceeds 5 lbs., shorten length of pushrod. If force required to seat gauge is less than 5 lbs. lengthen pushrod.
Ensure that pushrod is properly seated in booster when performing gauge check.
5.
Reinstall master cylinder and remove reservoir cover.
6.
Observe fluid surface when brakes are applied and released rapidly. If no movement is observed on fluid surface, pushrod is adjusted too long.
Fig. 2 Master cylinder pushrod adjustment. Delco-Moraine type vacuum booster