The brake booster system has two simple regular checks, vacuum hose and case. The entire power unit cannot be fixed; if it breaks, you need to replace it. Kick the brake pedal a few times with the engine shut off, watch if your pedal reserve distance holds steady, then begin your drive; when the pedal falls just a bit when you start the engine, that's how it should work. You can test your booster's airtightness by running your engine for two short minutes, turning it off, and pressing down the brake pedal slowly with several quick, repeated movements. If the pedal sinks initially but rises after two or three presses, you have fully sealed your booster. When the engine runs, press the brake pedal, then stop the engine with your foot on the pedal. If the pedal has identical spaces after being held down for 30 seconds, your booster valve is closed. To take out the booster, first take off the master cylinder, then on Durango cars, first remove the hood cover, then the support bar, and afterward disconnect the wiper motor's electric connection from behind the windshield. Separate the vacuum hose from the power brake booster without detaching the check valve, and then under the dash remove the power brake push rod from the brake pedal top by releasing the retaining clip. Taking out the nuts that hold the booster to the firewall, lift the unit off slowly from the firewall without pushing or pulling too hard. Keep track of where the gaskets were positioned between the booster and firewall. Insert the booster, screw on the locking nuts, attach the pedal positioner, bolt the master cylinder in place, join the vacuum hose, drain and restore the braking system, and finally test brake sensitivity.