When a vehicle shows up for service with a “noisy belt,” the usual assumption is that belt is trashed. But that is not necessarily so. It’s easy to blame the belt when it makes noise, but in reality the belt may be just fine - and trying to do its job, say officials at Gates Corporation, one of the world’s leading manufacturers of industrial and automotive products, systems and components.
Today’s serpentine belts are highly engineered to meet the rigorous demands that modern engines place upon them, they point out. “However, if you are still inspecting serpentine belts the way you inspect V-belts, your budget may be squealing as well.
“The belt has only one job to perform: to transfer power from the crankshaft to all of the accessories that it supports. The belt can be brand new, but if it’s not tensioned properly, it’s not going to transfer power correctly. That can create other problems in the Accessory Belt Drive System (ABDSystem), creating downtime and lost profits.”
Almost all new vehicles today have on-board diagnostics (OBD), including light duty trucks. By 2013, all Class 7 and 8 trucks will have OBD as well. Consequently, vehicle technicians face the challenge of tracking down the cause of the ubiquitous “Check Engine” error code. This typically misdiagnosed code is often caused by belt slip which is created by loss of belt tension either from a worn belt or a failing tensioner, Gates officials say. There are several reasons for this frequent misdiagnosis.
The error codes can originate in any of the sensors located in the system. A false code may send the tech on a goose chase assessing the wrong component. To make matters worse, there is very little information in the troubleshooting flow charts that indicates either belt slip or a failing tensioner as a potential cause of tension-related problems.
Over the last year, Gates, working with other vendors that manufacture components in the ABDSystem, has discovered some startling facts relating to these component failures. For example, a minimum of 20 percent of new and rebuilt alternators that are returned for warranty claims to the manufacturer are found, upon inspection, not to be defective and capable of charging properly when powered correctly. Either a worn belt, a failing tensioner, or both, caused the alternator to be returned unnecessarily for warranty replacement.
Another cause of system misdiagnosis is the result of a change in the manufacturing technology of the serpentine belts themselves, say Gates officials. Since the late 1990s, serpentine belts have been made with Ethylene Propylene Diene Monomer (EPDM) rubber instead of the neoprene material used previously. The EPDM belts have a significantly longer life. However, technicians who are familiar with neoprene-belt wear indicators - such as cracking and chunk-out - can misdiagnose the wear patterns on the newer EPDM belts.
SERPENTINE BELTS 101
A multi-ribbed serpentine belt represents a technological improvement over the standard V-belt that has been used on motor vehicles for a century, Gates officials say. The wider belt width and multiple ribs provide significantly more belt-to-pulley surface area to transmit torque to the components. The wedging action of the belt ribs into the pulley grooves creates friction that transmits power from the crankshaft to the various accessories in the system.
“Belt tension maintains this wedging force and is provided by either a manual adjustment or an automatic tensioner.”
In addition to the “Check Engine” warning, the equally vague description of “belt noise” is often the trigger that sends a vehicle in for service, note officials. Noise emanating from the serpentine belt can almost always be tracked back to a loss of tension in the ABDSystem.
“There are several things that can cause this reduced tension, and determining which ones are contributing to the problem is a little more difficult. A worn or wearing belt, misalignment in the system, incorrect manual tension or a failing automatic tensioner can all cause belt noise. And where there’s noise, there’s belt slip.”
Technical Editor Dave Cappert takes a look at timing-belt service, as well as some of the specialty tools required by some OEMs for the service.
Without question, today’s vehicle technologies far surpass those of a few decades ago. As good as technology is, it has a downside — neglect.