Chevrolet 25511548 BOOSTER

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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.

Install the retaining clip, and slide the eyelet end of the push rod on the pin on the brake arm.

A power brake booster has been available on all models since its introduction, utilizing vacuum from the engine manifold. It assists with brake applications by using stored vacuum in case of a fault in the booster.

Disconnect the vacuum hose leading to the front of the power brake booster and cover the end of the hose.