It used to be that two or three belts drove a few vehicle accessories.
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.”
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.
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.
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.
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.
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.
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.)