Why use an OADTM DECOUPLERTM pulley?

The OADTM DECOUPLERTM pulley, or OADTM, is a unique engine belt drive tuning device that can provide numerous significant benefits in a variety of engine and vehicle applications. These include:

  • extended belt life and increased drive system component durability by up to 2x.
  • extended tensioner life
  • quieter accessory drive system operation
  • smoother accessory drive system operation
  • reduced vibrations in passenger compartment

The OADTM pulley installs on the alternator and is a direct replacement for the standard alternator pulley.

The combustion cycle of engines inherently cause accelerations and decelerations of the crankshaft. The rotational speed of the crankshaft fluctuates with the ignition sequence in a sinusoidal pattern above and below the average RPM. The torsional vibrations that are transferred to the belt drive are caused by high rotational accelerations induced into the belt drive system via the crankshaft pulley. Because of these rotational accelerations, the especially heavy alternator rotor generates its own vibrations that can be felt throughout the vehicle. The Litens® OADTM absorbs, through the torsion spring, these vibrations and cancels out these high rotational accellerations. The dynamic forces within the system are therefore dramatically reduced and the belt tensioner as well as the entire system's durability is greatly increased.

Take another look at that pulley

Millions of late-model vehicles now require alternators equipped with OADTM pulleys rather than conventional solid or "one-way clutch" pulleys.

The OADTM Pulley is significantly different from any other "clutched" alternator pulley. Using another type of pulley in place of an OADTM pulley 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.

OAD Design
  • 1. CAP PLUG
  • 2. BUSHING
  • 3. SHAFT
  • 4. SPRING
  • 5. CLUTCH
  • 6. CARRIER
  • 8. PULLEY

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

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™ Decoupler™ 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.

An OAD™ Decoupler™ Pulley's internal spring and clutch mechanism absorbs the speed fluctuations encountered in a belt drive system. This system also disconnects (decouples) the alternators 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™ Decoupler™ 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™ Decoupler™ 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.)

An OAD™ Decoupler™ 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.

Failure to use a replacement alternator with an OE-design OAD™ Decoupler™ 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.

The OAD™ Decoupler™ 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™ Decoupler™ Pulleys for original equipment alternator manufacturers as well as customers in the replacement parts market.

Call your alternator supplier and verify that every alternator requiring an OAD™ Decoupler™ 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™ Decoupler™ 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.

There is no acceptable alternative to an OAD™ Decoupler™ 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.

The global fleet of OAD™ Decoupler™-equipped vehicles is now approaching 60 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.

No other manufacturers, in North America or around the world, produce OAD™ Decoupler™ 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™ Pulley technology, but the performance is not comparable in any way. These one-way pulleys do not adequately absorb drive belt system vibration.

OAD™ Decoupler™ 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.

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.


Not all Alternator Pulleys are created equal!

The Solid Alternator Pulley used to be the industry standard and has been around for many years. It has evolved from the V-type to the V-ribbed type (serpentine belt). Its only purpose is to drive the alternator via the belt.

If your alternator has a solid pulley, only replace if damaged, rusted or worn.

The Overrunning Alternator Pulley has a simple one-way-clutch inside the pulley. This internal clutch allows the rotor of the alternator to coast to a stop when the engine is shut down. This "overrunning" feature eliminates "chirp" sounds that happen when engine decelerates quickly causing the belt to slip at the alternator pulley (engine shut down or transmission shifting).

What to look for...

OAPs should spin freely in one direction and immediately lock in the other direction. Never replace an OAP with a solid pulley. The manufacture has designed the vehicle with it and damage to other components may occur if a solid pulley is substituted. Manufactures of simple OAPs include INA, NSK, Koyo etc.


The Overrunning Alternator Decoupler™ not only has a one-way clutch inside, it also incorporates a torsion spring to absorb energy. The effects of the internal clutch are the same as mentioned above; however, the patented internal torsion spring design is the key to the much higher level of function associated with the OAD™. The internal spring is tuned (engine specific) to absorb base engine vibrations (cylinder firing pulses) before they reach the alternator rotor and therefore negatively affect the accessory drive. With the OAD™ Pulley installed you will see much less tensioner motion, reduced NVH and an all around more robust accessory drive. Many manufactures are now including OAD™ Pulleys when designing their accessory belt drives. This allows them to use narrower belts with lower output tensioners. The lower system tension means the alternator, water pump, and other accessories bearings will last much longer.


What to look for...

OAD™ Pulleys should rotate freely in one direction and have a "spring feel" in the other direction. Since duty cycle and/or mileage are usually unknown when rebuilding the alternator, you should always install a new OAD™ Pulley at this time. This will ensure a quality rebuilt alternator and help eliminate field failures.

Never substitute a solid alternator pulley or a simple OAP in place of an OAD™ Pulley. The vehicle manufacture has designed the vehicle with this higher level of function for a reason! Substituting a different alternator pulley may cause damage to accessory drive components. The only manufacturer of the OAD™ Pulley is Litens Automotive Group®.


For Idler Pulley Assemblies there is a general Installation Procedure available. Please see below.

Installation Procedures