Take another look at that pulley

Millions of late-model vehicles now require alternators equipped with an OVERRUNNING ALTERNATOR DECOUPLER™ (OAD™) pulley rather than conventional solid or "one-way clutch" pulleys.

The OAD™ pulley is significantly different from any other "clutched" alternator pulley. Using another type of pulley in place of an OAD™ is a sure way to cause drive belt system problems.

To prevent damage to the vehicle, confirm that your alternator supplier always replaces OE design with OE design; if the vehicle requires an OAD™ pulley, be certain the unit you install features the same technology.

Here are a few Frequently Asked Questions regarding alternator pulley design for today's vehicles:

What does an OAD™ pulley do?

An OVERRUNNING ALTERNATOR DECOUPLER™ pulley helps "synchronize" the belt drive system for improved engine efficiency, reduced Noise/Vibration/Harshness (NVH) and increased component life.

When an engine accelerates, the alternator's mass creates resistance against the belt. In addition, due to differences in drive ratio between the crankshaft and alternator pulleys, alternator speed is typically three times faster than engine speed. These factors often cause "rope-tow effect" in which belt speed and alternator speed are out of phase. Belt tensioners can absorb some of the resulting vibration, but the belt ultimately bears the brunt of this damaging force.

An OAD™ pulley features a sophisticated internal spring and clutch system that absorbs the force associated with belt accelerations and tension reversals and permits the alternator to "free-wheel" or "overrun" when the belt suddenly decelerates.

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How is an OAD™ pulley different from a conventional pulley?

An OAD™ pulley's internal spring and clutch mechanism absorbs the speed fluctuations encountered in a belt drive system. This system also disconnects (?decouples?) the alternator?s rotational mass from the belt drive in cases of sudden belt deceleration. This "overrunning" or "free-wheeling" action eliminates damaging peaks in belt tension, enables the engine to operate more efficiently and helps minimize NVH. An OAD™ pulley is different from an Overrunning Alternator pulley, or "one-way clutch." Although both of these technologies allow the alternator to free-wheel when necessary, only an OAD™ pulley also includes the internal spring mechanism required to absorb vibration caused by reduced belt tension. (By reducing belt tension in their latest models, automotive engineers have been able to increase engine efficiency and fuel economy.)

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How can I tell the difference between an OAD™ pulley and a one-way clutch?

An OAD™ pulley should rotate freely in one direction and offer limited, spring-like movement in the other direction. A one-way clutch will only rotate in one direction.

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What will happen if I use another type of "clutched" pulley or solid pulley on an OAD™ application?

Failure to use a replacement alternator with an OE-design OAD™ pulley can lead to extreme belt tension issues, severe vibration and extreme NVH. Ultimately, this "mechanical virus" can damage other, more expensive, components within the belt drive system.

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Who manufactures OAD™ pulleys?

The OAD™ pulley design is patented by Litens Automotive Group, a global manufacturer of original equipment and replacement components for the transportation industry. Litens is also the exclusive manufacturer of OAD™ pulleys for original equipment alternator manufacturers as well as customers in the replacement parts market.

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How do I know my alternator is supplying the correct pulley design for each vehicle I service?

Call your alternator supplier and verify that every alternator requiring an OAD™ pulley is equipped with one. As this technology becomes more prevalent, it is wise to remind your supplier with each alternator order that the part you need should include an OAD™ pulley. In fact, Litens recommends that jobbers and their customers confirm that their alternator suppliers always utilize OE-design pulleys with every new or remanufactured alternator, whether the application requires an OAD™ DECOUPLER™ pulley, and OAP pulley or other design.

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My supplier says their pulley design is "just as good" as an OAD™ pulley. Why should I worry?

There is no acceptable alternative to an OAD™ pulley. This patented design offers exclusive benefits that cannot be provided by another type of pulley. Use of another type of pulley could lead to serious and expensive issues in the drive belt system.

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Currently how many vehicles in operation are equipped with an OAD™ pulley?

The global fleet of OAD™ pulley equipped vehicles is now approaching 20 million, with approximately half of those in North America. This number is expected to rise by approximately 25 percent in each of the next several years.

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What other manufacturers (other than Litens) produce OAD™ pulleys?

No other manufacturers, in North America or around the world, produce OAD™ pulleys. This technology is fully protected by patents and intellectual property laws. Some other manufacturers attempt to market their "Overrunning Alternator pulley" (OAP) as an alternative to OAD™ technology, but the performance is not comparable in any way. These one-way pulleys do not adequately absorb drive belt system vibration.

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What type of testing/specifications are required by vehicle and engine manufacturers using OAD™ pulleys?

OAD™ pulleys pass a rigorous series of tests to ensure exceptional performance and durability. These tests include: lug test, start-stop, wide-open throttle shift simulation, and 3,000-hour D4 speed change test. Others include brutal salt spray and mud resistance evaluations.

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What is the expected service life of an OAD™ pulley?

Early design versions have provided service life of 40,000 to 60,000 miles. More recent versions often last more than 100,000 miles. Service life of each unit is based on operating conditions, style of driving, etc.

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Solid Pulley vs. OAP (One-Way Clutch) vs. OAD™

This comparison of three leading alternator pulley designs demonstrates the danger of using the wrong type of pulley on a vehicle requiring an OAD™ pulley.

Note the severe level of belt drive vibration (see whiplashing belt tensioner) when a "solid pulley" is installed on the belt drive system.

Similarly, the use of an "OAP" ("one-way clutch") on this application also results in significant belt drive vibration, causing NVH issues and wear of key components.

This footage shows a Litens OAD™ pulley on the same application. Note the smooth, efficient, low-stress operation of the belt drive system.

Alternator Pulley Comparison

This video demonstrates the excessive levels of NVH, belt system stress and other severe issues resulting from the use of a solid alternator pulley on this Ford engine.

This clip shows the use of a variety of "one-way clutch" alternator pulleys on the same engine.

Now we see the smooth, efficient operation of the same engine belt drive system using an OAD™ pulley. The Liten OAD™ pulley was previously referred to as an isolating decoupler pulley or IDP and marketed under the RotorRX brand.

Solid Alternator Pulley Demonstration

This engine requires an overrunning alternator decoupler (OAD™) pulley. To show the importance of using the right pulley design, we installed an alternator equipped with a solid pulley.

Notice the severe vibration in the belt drive system. This condition will cause a loss of engine efficiency/fuel economy, shortened belt and bearing life, extreme NVH, and other problems.

One-Way Clutch (OAP) Demo

This is a closeup view of the belt tensioner on a vehicle equipped with the wrong alternator pulley design - a "one-way clutch" (OAP). This engine requires an overrunning alternator decoupler (OAD™) pulley.

Note the significant vibration and stress on the belt tensioner. This condition will likely lead to unsatisfactory levels of NVH and reduced component life.

Litens OAD™ Closeup

This tight view of an alternator equipped with a Litens overrunning alternator decoupler (OAD™) pulley shows how the patented spring-loaded mechanism absorbs belt drive vibration.

This innovative design - required on millions of vehicles - boosts engine efficiency and helps eliminate NVH issues.

It is never appropriate to use another alternator pulley design in place of an OAD™ on vehicles originally equipped with this technology.

This video was created using a strobe light to see how the OAD™ pulley compensates and absorbs the engine pulses being transmitted by the belt to the alternator rotor.

Benefits of OAD™ Pulleys

Several vehicle manufacturers now specify isolating decoupler pulleys (IDP) or Litens' overrunning alternator decoupler (OAD™) pulleys for their latest engines due to the extremely smooth, efficient belt drive performance made possible by this technology.

It is never appropriate to use another alternator pulley design in place of an OAD™/IDP on vehicles originally equipped with this technology.

Vehicle Makes/Models Requiring DECOUPLERS™
  • Chevrolet Cobalt   • Chevrolet Corvette   • Chevrolet Malibu   • Chrysler Pacifica   • Chrysler Sebring   • Dodge Caliber   • Dodge Caravan   • Dodge Prowler   • Jeep Compass   • Jeep Liberty KJ   • Jeep Patriot   • John Deere 4.5L Tractor   • Lexus GS   • Lexus IS   • Lexus ES   • Pontiac G6   • Pontiac Solstice   • Pontiac Vibe   • Saab 9-3   • Saab 9-5   • Saturn Ion (Redline)   • Saturn Sky   • Toyota Avalon   • Toyota Camry   • Toyota Corolla   • Toyota Matrix   • Toyota RAV4   • Toyota Sienna   • Toyota Solara   • Volvo V70   • Volvo XC90   • Volvo S80