Depress the brake pedal several times with the engine off to ensure there is no change in the pedal reserve distance. Start the engine while depressing the pedal; if it goes down slightly, operation is normal. After running the engine for one or two minutes, depress the brake pedal several times slowly; if the pedal goes down farther the first time but gradually rises after the second or third depression, the booster is airtight. While the engine is running, depress the brake pedal and then stop the engine with the pedal still depressed; if there is no change in the pedal reserve travel after holding it for 30 seconds, the booster is airtight. The power brake booster unit requires no special maintenance apart from periodic inspection of the vacuum hoses and the case, and if a problem develops, it must be replaced. To remove the booster, first, remove the battery and the air filter housing, then disconnect the vacuum hose from the power brake booster by pulling straight forward, ensuring to inspect and replace the grommet if necessary. Next, remove the master cylinder, disconnect the power brake pushrod from the top of the brake pedal by prying off the retaining clip, and discard the old clip for safety. Remove the nuts attaching the booster to the firewall, disconnect the brake booster pushrod from the brake pedal arm, and carefully withdraw the power brake booster unit from the firewall and out of the engine compartment. For installation, place the booster into position on the firewall and tighten the retaining nuts, then connect the pushrod to the brake pedal, install the master cylinder, and bleed the brake hydraulic system. The remaining installation steps are the reverse of removal, and it is important to carefully test the operation of the brakes before placing the vehicle in normal operation.