I just bought my '05 F-150 FX4 a few months ago and have just recently noticed something odd.
It drives perfectly fine, but I was just taking a look at the engine while the truck was running and noticed that one of the "pulleys" that the belt is connected to is kind of wobbly. Not a whole lot, but it moves a little bit. I've tried tightening it down but it's already as tight as it will go. Should this be something to worry about?

 

There are 2 pulleys that control the tension on the belt. They are about 3" in diameter. One is the idler pulley and one is the tension pulley. Both are prone to bearing failure. I'd change them both since no wobble should be present. They could freeze up at any time and snap the belt. Good luck.

 

Thank you! Is there a specific brand that's best for the replacement? Or is Motorcraft the way to go?

 

I've always used what ever brand was available at the local parts store. Motorcraft however, is higher in cost, but will always insure the correct fit.

 

I would rather spend a little more to ensure a correct fit. One last question. I am overseas now and not able to check my truck to see and I'm seeing on diagrams of the '05 5.4L engine that there are 2 smooth idler pulleys and 1 grooved. Is this correct?

 

Yes you are correct. Facing the motor there is one smooth pulley at upper right and upper left. Here's a link to an image of the belt routing. http://www.2carpros.com/questions/2005-ford-f-150-drive-belt-routing-54-engine

 

Awesome. Thank you! I do appreciate your help!