GMC 84472897 Power Brake Booster ASSEMBLY

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To test the vacuum booster, start the engine and press the brake pedal to see if it goes down slightly. Repeat this with the engine running to check for changes in pedal reserve distance. For airtightness, start and stop the engine, then press the brake pedal slowly multiple times. If the pedal reserve travel doesn't change after 30 seconds, the booster is airtight. For hydraulic boosters, turn off the engine, press the brake pedal to deplete accumulator pressure, then apply 40 pounds of force to the pedal and start the engine. If the pedal sinks and rises, the booster is fine. If not, check the power steering fluid and hoses. If these are fine, the booster or pump may be faulty. To remove the booster, disconnect the battery, deplete accumulator pressure, detach hoses, and remove the master cylinder. Disconnect electrical connectors, remove the pushrod and the four nuts holding the booster. Remove the booster and gasket. Install with a new gasket and tighten to the correct torque. For hydraulic boosters, bleed the power steering system and check fluid level.