Wipe the entire inner surface of the serpentine belt with a clean rag and examine it for cracks and frayed fiber. You may wish to replace if it looks badly worn or glazed. Loosen the 5/8-inch locking nut on the pulley adjustment stud with an end wrench.

Unscrew the 5/16 adjusting stud with and end wrench to loosen the belt. If you need to replace the belt, make a note of belt orientation around the other pulleys, or consult your repair manual for their positions. Place the new belt around the pulleys and slip it over them.

Turn the 5/16 adjusting stud until the belt begins to tighten. Measure the deflection of the belt at its longest travel length between pulleys. Push your thumb lightly against the belt and measure the movement with a ruler. You should have no more than 1/4 inch, or 6 mm deflection.

Take a more accurate reading with a belt tensioner gauge. Place the gauge hook in the middle of the long part of the belt and pull back on the tool. The gauge needle will measure the pull movement on a scale. Again, no more than 1/4 inch or 6 mm can be allowed. Hold the 5/16 adjusting stud with an end wrench while you tighten the 5/8-inch locking nut with another end wrench.