Chevrolet 25511548 BOOSTER

Disconnect the booster push rod from the brake pedal arm by removing the retaining clip, and sliding the eyelet end of the push rod off of the pin on the brake arm. Disconnect the master cylinder from the booster. Remove the attaching nuts and remove the booster from the firewall. Install the booster on the firewall and tighten the nuts to 22-33 ft. lbs. (29-43 Nm). Connect the master cylinder to the booster. Connect the booster push rod to the brake pedal arm by installing the retaining clip, and sliding the eyelet end of the push rod on the pin on the brake arm.

A power brake booster is standard across all models and came with the vacuum system derived from the manifold of the engine. Ideally, vacuum is accumulated in case of a failure in the booster to manage two or three brake applications after which more force such as in any hydraulic system is applied to the brake pedal. Other types of power brake boosters are the Delco-Moraine and Bendix boosters and both work in a similar manner. When the brakes are released the vacuum is possible on both sides of the power piston, the air through the filter enters, and in turn, any air in the circuit is drawn through a narrow passage and into the intake manifold by means of a check valve. When the brake pedal is pressed, this pushes the push rod that in turns moves the air valve thus opens to allow air from the environment into the housing so as to motivate the power piston to operate the hydraulic master piston. As pressure increases the hydraulic reaction plate comes in contact with the reaction levers to feedback to the pedal that the degree of brake has been applied for the driver to feel. When the required braking force has been realized, the power piston stops moving in case of alteration of pressure on the pedal. Venting pedal pressure returns the air valve to engage the power piston thus sealing off supply of atmospheric air and with the help of piston, the hydraulic pressure inside the brake system is relieved by receding into the rear housing. Should there be vacuum failure for instance when the engine is off or when there is a bad vacuum line then the brake pedal can still be applied though at a higher pedal pressure that a normal system. The power brake unit does not need any special degree of maintenance, apart from the inspection of the hoses and the air filter located beneath the boot on the side of the push rod from the pedal. Removal of the power brake unit requires special tools and it is best to get a new or re-manufactured unit as replacement on the occurrence of a problem if not warrantied by the company.

Remove the securing nuts that hold the master cylinder to the power brake unit and position the master cylinder out of the way, taking care not to strain the hydraulic lines. If there is any doubt about the flexibility of the fluid lines, disconnect them at the cylinder and plug the ends. Disconnect the vacuum hose leading to the front of the power brake booster and cover the end of the hose. Loosen the four nuts that secure the booster to the firewall without removing them at this time. Inside the car, disconnect the power brake push rod from the brake pedal without forcing it to the side. Fully remove the four booster mounting nuts and carefully lift the unit out of the engine compartment. For installation, loosely install the four mounting nuts, connect the push rod to the brake pedal, torque-tighten the attaching nuts, and reconnect the vacuum hose and master cylinder. If the hydraulic brake fluid lines were disconnected, the master cylinder and the entire braking system should be bled to eliminate any air that has entered the system.

Remove the securing nuts that hold the master cylinder to the power brake unit and position the master cylinder out of the way, taking care not to strain the hydraulic lines. If there is any doubt about the flexibility of the fluid lines, disconnect them at the cylinder and plug the ends. Disconnect the vacuum hose leading to the front of the power brake booster and cover the end of the hose. Loosen the four nuts that secure the booster to the firewall without removing them at this time. Inside the car, disconnect the power brake push rod from the brake pedal without forcing it to the side. Fully remove the four booster mounting nuts and carefully lift the unit out of the engine compartment. For installation, loosely install the four mounting nuts, connect the push rod to the brake pedal, torque-tighten the attaching nuts, and reconnect the vacuum hose and master cylinder. If the hydraulic brake fluid lines were disconnected, the master cylinder and the entire braking system should be bled to eliminate any air that has entered the system.

A power brake booster has been incorporated in all models since its release with vacuum sourced from the engine manifold. There is sufficient vacuum stored to help out in two or three emergency stop applications of the brakes after which higher pedal pressures will be required by the Hydraulic brake system for a faulty booster. Delco-Moraine and Bendix power brake boosters work in almost the same way but may be of different designs. When brakes are released with the engine 'On', the vacuum is created on both sides of the power piston; the supply of atmospheric air is through a filter and stopped at the air valve. When the brake is applied the pedal presses the push rod to change the position of the air valve so that fresh air can enter and push the power piston to work the hydraulic master cylinder. The hydraulic reaction plate then relays information to the pedal so the driver can determine the intensity of the brake beings used. The power piston thus only moves until the braking force required is obtained and then stays at that position until there are changes in pressure from the pedal. When the pedal pressure is released the air valve returns to a position with the power piston, closes atmospheric air from the hydraulic brake system and the piston comes back to its initial position and reduces hydraulic pressure in the brake system. In the event when the vacuum supply fails such as during engine-off condition, the brake pedal can be depressed and it requires much higher brake pedal pressure similar to that of the standard anti lock braking system. The power brake unit has no regular maintenance that has to be done other than ocular inspection of the brake hoses and replacement of the filter. Removing the unit requires certain tools and it is more reasonable to fit in a new or ex-factory model than repair the initial booster if a problem arises.