Drive Belt

The drive belt turns the pulley on the alternator and may connect to other accessories such as the water pump and air conditioning (A/C) compressor. Belts come in two types: serpentine and V.

Drive Belt Diagram. A drive belt diagram is commonly located on an engine compartment label.

Serpentine Belt. A serpentine belt, also called a multi-ribbed belt, is flat on one side and has grooves that run parallel with the belt on the other side. Commonly, serpentine belts will have 2 to 8 grooves on one side and are usually ½ to 1 inch (1.27 to 2.54 cm) wide depending on the number of grooves and application. Serpentine belts are usually constructed of Neoprene material or EPDM (Ethylene Propylene Diene Monomer) rubber. Neoprene belts crack and lose rib pieces when worn. EPDM wears similar to a tire, losing rubber, but not necessarily cracking. An EPDM belt that isn’t cracked or visibly damaged, could still be worn out and need replacing.

V-Belt. In contrast, a V-belt is usually less than ½ inch (1.27 cm) in width and has a cross-section that looks like a “V”.

Automatic Belt Tensioner. The automatic belt tensioner, a critical component in the belt drive system, keeps a serpentine belt tight with the correct amount of tension and minimizes vibrations. Tensioners wear over time and must be replaced. If the tensioner spring is worn the belt can slip creating excessive heat – glazing the belt’s surface. Glazing leads to belt squealing. A worn tensioner spring will exhibit excessive vibrations when the A/C is on. If the bearing on the tensioner is worn, the belt may get out of alignment causing side wear and fraying. Worn bearings can also put stress on the alternator, water pump, A/C compressor, or other accessories – resulting in premature component failure.

Belt Wear. A worn belt can slip, hydroplane, elongate, or become misaligned. Worn belts can have side abrasion from misalignment, cracking, glazing, or pilling.

Buying Belts. When buying a new belt check the number of accessories the belt goes around, if it is V or serpentine, and note the factory numbers on the old belt to assist in cross-referencing.