Since the advent of the automatic belt tensioner system, the labour time of manual belt adjustment has been significantly reduced. The belt tensioner on Ford cars and trucks, as well as other vehicles, keeps the serpentine belt tightened to the correct tension and absorbs shock when the air compressor gets turned on. A bad pulley bearing, or a broken or worn tensioner spring, can spell disaster for the rest of the accessories that run off the serpentine belt. Failing belt tensioners can allow the belt to slip, crack and eventually fall off, disabling the water pump, power steering pump, alternator and air compressor.
Place the vehicle in "Park" or "Neutral," with the emergency brake set. Raise the hood. Disconnect the negative battery cable from the post. For the Ford model that has a side-mounted engine, loosen the lug nuts with a tire iron on the wheel that faces the front of the engine. Lift the side of the vehicle with a floor jack high enough for some clearance. Place a jack stand under the frame, on the inboard side of the wheel. Finish removing the lug nuts on the wheel; pull it loose, and set it aside.
Remove the splash guard on the inside of the wheel well, using the proper socket and wrench. If the splash guard has clips and screws, remove them with the appropriate size Phillips screwdriver. Go to the engine compartment, and place a Ford-type belt tensioner tool onto the tensioner pulley. The tensioner tool will have the correct size socket that fits over the pulley bolt.
Place the socket over the bolt, and turn the long-handle of the tool to unload the belt pressure. Slip the belt off the pulley with your other hand, while keeping tension on the lever. Remember the exact routing of the serpentine belt. Do not remove it; let it hang loose. Refer to your owner's manual for the belt routing diagram, or look on top of the fan shroud for the proper routing placement.
Go to the wheel well, and use a socket attached to an extension and a ratchet wrench to loosen the tensioner pulley bolt. You might have to slam the ratchet handle hard, counterclockwise, to break the bolt loose. Pull the pulley off the shaft. Use the same extension and ratchet to remove the bolt on the belt tensioner housing. Turn counterclockwise, and unscrew it. Remove the housing. Place the new housing against the mount (align the slot, if it has one), and run the bolt in, by hand. Tighten the bolt with the ratchet, socket and extension.
Place the new tension pulley on the shaft, and start the bolt by hand. Finish tightening the bolt with the wrench, socket and extension. Place the splash guard back into position, and refasten the screws (or bolts) with the proper screwdriver or socket.
Move to the engine compartment. Use the belt tensioner tool to load the tensioner pulley, by placing the socket over the bolt head and turning it to load it against the spring pressure. While holding it, slip the serpentine belt back over the pulley, aligning it with the grooves. Release the belt tension. Place the wheel back on the hub, and tighten the lug nuts (snug tight only).
Use the floor jack to lift the frame, and remove the jack stand. Finish tightening the lug nuts with a torque wrench to the manufacturer's specifications. Reconnect the negative battery cable with an end wrench. Start the engine, and look for proper belt tensioner operation and correct pulley alignment.