Auto Service World
Feature   June 1, 2010   by Auto Service World

Serpentine Belt Wear Inspection (June 01, 2010)

With the advent of new materials, the very nature of serpentine belt wear and failure has changed.

Itself a sign of changing times–who here remembers when a series of V-belts drove everything under the hood?–the serpentine belt has continued to evolve, mostly in materials and wear characteristics.

In large part, neoprene has given way to Ethylene Propylene Diene Monomer (EPDM) as a material of choice.

Neoprene belts were great by their contemporary standards: they lasted up to 100,000 kilometres, and would show signs of cracking before ultimate failure (three or four cracks an inch and it was time to change out). Yes, they were prone to losing chunks of material at the end of their useful life, but this was a better alternative to total failure without any warning signs.

But, with the move to EPDM in the late 1990s, technicians and experienced do-it-yourselfers that had become used to such simple diagnostic checks on serpentine belts had to do an about-face.

The fact is that EPDM belts are longer lasting–with a lifespan in the range of 160,000 km, notwithstanding extreme conditions and physical damage from road debris–which means that in many cases shops may have only started seeing the replacement cycle in any volume within the last few years.

EPDM belts are not prone to chunking or cracking. Instead, they gradually wear out.

This wear can be hard to inspect for. “How worn is too worn?” is a tough question to answer.

To help technicians and others answer the question, two major belt suppliers have come up with ingenious tools.

Both Gates and Dayco have special belt wear gauges that can speed the diagnosis of a worn belt, and provide a means for shops to communicate with the consumer.

In both cases, a small plastic gauge is used to measure the depth, evenness, and profile of the valleys in the drive side of the serpentine belt.

The reasons for this approach are simple: EPDM belts wear as they age. Although the ribs do not become shorter, material is lost in the valleys of the ribs, making the space between ribs wider. More precisely, the rib valleys go from a V shape to more of a U shape.

As more material is lost, the pulleys ride deeper into the belt valleys, resulting in slip, noise, and hydroplaning. With sufficient material loss, the pulley ribs “bottom out” in the valleys and ride on the belt cord. This reduces the surface contact on the valley sides, where the traction is generated. Wear also increases the effective belt length, lowering the tension in the system, which also reduces traction.

And, in addition, they can exhibit other symptoms that are caused by problems with the accessory drive–such as tensioner misalignment or failure, pulley misalignment, excessive heat, or bearing failure in one of the other components. If the belt exhibits abrasion, cracking, glazing, or pilling, it needs to be replaced. If it fails, it could damage other system components, in addition to stranding the motorist.

According to Gates, many warranty-claim failures on alternators and other parts are actually caused by worn or improperly adjusted belts.

One important fact that has not changed in the evolution to new materials is the fact that when a serpentine belt breaks, the car stops. This is an outcome that nobody wishes on the car owner.

Employing the proper inspection techniques is an important part of ensuring that doesn’t happen.

Special thanks to Gates Corporation and Dayco Canada for information used in this article.


The Gates serpentine belt wear inspection tool is a nifty orange plastic unit. You can slip your finger through the oval hole and press the long strip into the grooves of the belt. If it goes all the way in, it’s time to replace the belt.

The Dayco “AWearness” tool has a similar main function, but is a bit of a multitasker, too. The bar joining the two sides of the “U” is used for checking groove depth–if the flat portion can be pressed level against the belt when the bar is in the groove, belt replacement is in order. The tool also allows for checking groove profile with the sharp “teeth” and the space in the “U” is one inch, good for counting belt cracks (more than four means it’s replacement time.)

While the design of two ingenious inspection tools differs, in the case of both the Gates and Dayco serpentine belt wear gauges the important thing to remember is that they are not to be treated like tire wear gauges. With tire wear, you measure tread depth: the deeper the gauge goes, the better. With serpentine belt wear gauges, the opposite is true: if the gauge sinks all the way into the rib valley, the belt is worn and should be replaced.

If there is a great deal of variation between the ribs, it is a likely sign of pulley misalignment that should be rectified.


Timing is Everything for Aging Belts

The correct time to change a timing belt in older cars depends not only on the mileage of the car, but also on the age of the belt, says ContiTech’s Power Transmission Group.

“Long periods of inactivity place just as much strain on a belt as regular operation,” says Helmut Engel, head of Automotive Aftermarket at ContiTech’s Power Transmission Group. “Aging damages the material of chloroprene belts–no matter how much you drive. Many drivers don’t realize that just because your owner’s manual says you should make a regular trip to the repair shop, many cars are unlikely to reach the replacement intervals specified by the manufacturer, even after many years of driving.”

“In the last few years, some manufacturers have already started to change replacement intervals to take age into account, especially for timing belts. However, these changes are not always indicated in the service manual,” says Roger Homer, ContiTech’s director of North America business development. “In order to perform maintenance in accordance with the inspection guidelines, repair shops should always refer to up-to-date information.”

If the manufacturer has not provided suitable specifications, ContiTech advises that timing belts used in older cars be replaced after six years at the latest.

“When changing belts, it is also highly recommended to replace all the relevant belt drive components at the same time,” says Homer. The company offers kits containing matched drive components to achieve this. “This provides greater safety for the engine. The advantages for service shops are clear: there is no need to order individual parts, you can always be certain that the parts match the vehicle and type, and administration for incoming goods and processing becomes a lot simpler.”

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