The Moen 7400 series of kitchen faucets features single-handle kitchen faucets available in a wide variety of designs. As a corporation, Moen is famous for its single-handle faucets, with the first one being developed by company founder Al Moen in 1937. Unfortunately, even the best faucets will eventually wear out and need to be replaced. While you can call a plumber to do the job, that will take time and cost money. There is no reason anyone with the ability to use a wrench and a little guidance can't replace her ailing 7400 series faucet herself.
Reach under your kitchen sink and locate the shutoff valves for your hot and cold water supplies. Close the valves to shut off the water to your kitchen faucet. Turn the faucet on to expell any water still trapped in the lines. Get comfortable as you will be spending most of your time under the sink.
Unscrew the water lines from the faucet supply tubes, using your adjustable wrench. The tubes hang down below the underside of the sink. If your old 7400 faucet has been in place for awhile the nuts on the water lines may be corroded in place. If so use a penetrating oil to loosen the nuts before unscrewing them. Once they are disconnected, just lay the water lines down on the bottom of your kitchen sink.
Remove the retaining nut holding the faucet in place. Most models in the 7400 series have a single nut attaching the faucet to the sink. It is on the underside of the sink, in between the water supply tubes. Unscrew the nut, again using penetrating oil if needed, and remove it. Some models in the 7400 series also use a deck plate between the nut and the sink. If your model has one, remove the deck plate as well. It may be helpful to use a basin wrench as well, as it will allow you to reach up and behind the sink if need be.
Slide the faucet out of its mounting holes in the top of the sink. Remove the rubber gasket that rests between the faucet and the sink. Discard your old 7400 faucet and thoroughly clean the mounting area on your sink.
Place a small amount of plumber's putty around the area where you will be installing the new faucet. This will help create a watertight seal. Place the rubber gasket on over the mounting holes and slide the new faucet through the mounting holes. Turn the faucet spout to one side to prevent the faucet from tipping forward while you are attaching the nut underneath the sink.
Climb under the sink and replace the deck plate and retaining nut. Reconnect the water supply lines. On the 7400 series the hot water line connects to the left supply tube on the faucet. If you are replacing your old 7400 with a different model, refer to that model's documentation to see which tube is the hot water supply. Open the shutoff valves and turn the faucet on to ensure it is working properly.