It used to be that two or three belts drove a few vehicle accessories.
Not anymore. A single belt is now used to run more accessories than ever. And these days, both sides of a belt are being used to drive accessories and that means belts are working harder than ever. It also means they’re important than ever. With this in mind, if a single belt fails, it can be catastrophic.
“Belt noise is like a ‘check engine’ light that something is wrong within the drive system,” said Robert Christy, director of marketing, Dayco Products. “Diagnosing drive noise has become more complicated than ever before because of the complexity of today‘s drive systems and the number of accessories a belt is asked to drive. Many times the belt is the symptom not the cause.”
Accessory drive belts transmit engine torque to an assortment of pulley-driven accessories including the water pump, alternator, power steering, air conditioning and air injection pump. In addition to the effects of high underhood temperatures and atmospheric air pollution, frequent use of the air conditioner compressor, power steering pump or alternator tend to accelerate wear on the drive belts.
Serpentine belts of the past were made with Neoprene and lasted between 50,000 to 80,000 miles. In the past, serpentine belts, which are critical to running all these accessories, were to be replaced when an inspection showed at least four cracks per inch. Other belt issues that required replacement included chunking, rib glazing, and backside wear or splitting.
These days, belts are made with EPDM, or ethylene propylene diene Monomer (M-class) rubber. EPDM belts are extremely resistant to heat, ozone and weather, and as such, can last up to 100,000 miles. But like any belt, they eventually must be replaced.
EPDM belt wear can be more difficult to assess. New EPDM belts will exhibit the typical “V” profile in its ribs. In one that is worn however, the “V” profile will look more like a “U.” This is due to material lost from the rib. Once this happens, there is less material to come in contact with the pulleys, which can lead to slippage. This affects the performance of accessories and causes the tell-tale noise that motorists complain of.
Noise is often the first thing motorists notice about belts when something’s awry. But it’s not always the belt’s fault.
The noise generated from an accessory drive isn’t always caused by the belt itself. It’s a common perception that merely changing a belt will remedy any belt problem. Not so. Belt noise can actually be caused by a number of problems.
If misalignment and tensioning aren’t remedied or the drive isn’t inspected to find the real problem, you’ll often find a customer returning to say the belt is at fault.
There are basically two types of belt noise: chirp and squeal. Both noises mean different things. “Chirp” is generally understood to be a sound that is sharp and intermittent. Chirp can be recognized because as the belt speed increases, the pitch and volume of the chirp remain the same. One cause of chirp is often misalignment between the pulleys on a drive.
There can also be other causes of chirp, such as worn pulley bearings, improper installation and worn ribs. Leaking fluid from other components also can contaminate the belt and lead to the chirping noise.
Squeal, the most commonly heard belt noise, is high-pitched in nature, and can last several seconds. Like chirp, squeal’s pitch does not change, but unlike chirp, its volume can differ. Squeal be both continuous or intermittent. It also can change when the vehicle accelerates or another accessory is turned on (A/C, for example.)
