Question about 2003 Ford F250 Super Duty Crew Cab
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Posted on Jan 02, 2017
Check the brake fluid first.is it low or no brake fluid at all.is the brake fluid got dried up or leaked out.
Sounds like the power brake booster is bad, that is what the master cylinder is bolted too. There is a rubber hose that has a plastic valve in it were it snaps into the booster, Pull that rubber hose out of the booster and off of the engine, Now the end that you took off the engine. You should be able to **** through the line, but not be able to blow through it. If you can then replace the valve, It is a one way valve.
If that is all right then hook hose back up to the engine and start engine, You should hear a major vacuum leak at the valve end, put you finger over the valve and it should stop making noise and engine should smooth out. If it don't the rubber hose must be leaking or the tube on the engine were the hose hooks to is stoped up. Also check the master cylinder if power booster is replaced. If the brake light is coming and going check the brake light switch. check fig for the internal assembly parts:--
To check engine vacuum, connect a vacuum gauge to the supply hose that runs from the intake manifold to the booster. A low reading (below 16 inches) may indicate a hose leak or obstruction, a blockage in the exhaust system (plugged catalytic converter, crushed pipe, bad muffler, etc.), or a problem in the engine itself (manifold vacuum leak, bad valve, head gasket, etc.).
The condition of the diaphragm inside the booster is also important. If cracked, ruptured or leaking, it won't hold vacuum and can't provide much power assist. Leaks in the master cylinder can allow brake fluid to be siphoned into the booster, accelerating the demise of the diaphragm. So if there's brake fluid inside the vacuum hose, it's a good indication the master cylinder is leaking and needs to be rebuilt or replaced. Wetness around the back of the master cylinder would be another clue to this kind of problem.
To check the vacuum booster, pump the brake pedal with the engine off until you've bled off all the vacuum from the unit. Then hold the pedal down and start the engine. You should feel the pedal depress slightly as engine vacuum enters the booster and pulls on the diaphragm. No change? Then check the vacuum hose connection and engine vacuum. If okay, the problem is in the booster and the booster needs to be replaced.
Vacuum boosters also have an external one-way check valve at the hose inlet that closes when the engine is either shut off or stalls. This traps vacuum inside the booster so it can still provide one or two power assisted stops until the engine is restarted. The valve also helps maintain vacuum when intake vacuum is low (when the engine is under load or is running at wide open throttle). You can check the valve by removing it and trying to blow through it from both sides. It should pass air from the rear but not from the front.
Replacing a vacuum booster is a fairly straight forward job. All you have to do is disconnect it from the brake pedal on the inside and unbolt the master cylinder. The pushrod that runs from the booster into the back of the master cylinder must have the specified amount of play.
You will typically find the power brake booster mounted on the firewall attached to the master cylinder. The master cylinder is connected to the brake pedal.
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Posted on Jul 15, 2010
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