Drive Belt
A flexible rubber belt driven by the crankshaft that transfers rotational power to engine accessories like the alternator and water pump.
A drive belt (also known as an accessory belt) is a heavy-duty, reinforced rubber belt that loops around pulleys on the engine's crankshaft and various accessories. Its job is to transfer the rotational power of the running engine to drive components such as the alternator, power steering pump, water pump, and air conditioning compressor. Modern vehicles typically use a single, wide serpentine belt, whereas older vehicles may use multiple individual V-belts.
Drive belts are made of durable synthetic rubber compounds (like EPDM) reinforced with internal cords for tensile strength. They are subjected to extreme heat, tension, and rapid speed changes. Over time, the rubber degrades, leading to cracking, fraying, splitting, or dry rot. If a drive belt slips, it can cause battery discharge (alternator slip) or heavy steering (power steering pump slip). If it breaks completely, the engine accessories stop working immediately, which can lead to rapid overheating if the water pump is driven by the belt.
Mechanics inspect drive belts during routine maintenance, checking the rib side for cracks and checking belt thickness with a wear gauge. Replacing a drive belt is a preventative maintenance task that should be done according to the manufacturer's mileage interval or when squealing noises or visual wear are detected. The belt tensioner and idler pulleys should also be checked when replacing the belt.