As more and more automotive original equipment manufacturers turn to lean belt drive systems to improve fuel efficiency, it’s crucial that technicians are prepared to service the new technologies that help them run. One critical component...
As more and more automotive original equipment manufacturers turn to lean belt drive systems to improve fuel efficiency, it’s crucial that technicians are prepared to service the new technologies that help them run. One critical component is the overrunning alternator decoupler (OAD), which requires a different skill set and special tools for replacement compared with a regular pulley.
OADs are now beginning to come due for replacement. How well do you know OADs and their proper replacement procedures? The OAD helps to reduce overall belt drive system tension, resulting in lower hub loads on all of the bearings within the system, including the water pump, power steering pump, tensioner pulley, routing idlers and, of course, the alternator bearings. Without the OAD, the vehicle could experience excessive belt flutter, worn or broken tensioners, extreme belt wear, belt ejection, unwanted noise from belt slippage and vibrations that can be heard and felt by the driver.
Why OADs? First, a little background. In recent years, OEMs have been using larger alternators in vehicles (160 to 200 amps vs. 60 to 70 amps a decade ago) to power “infotainment” items such as DVD players and electronic information systems, as well as heated seats and heated windshields. Additionally, OEMs are increasingly adopting smaller engines that improve fuel economy, but also inherently make the belt drive much rougher than on a larger engine. The combination of larger alternators with more mass and smaller, fuel-efficient engines presents challenges to the belt drive system—among them belt slip, belt chirp and increased vibration.
However, through the use of OADs, car manufacturers are able to implement a lean belt system (lower belt tension, smaller tensioners, narrower belts and pulleys) to reduce component cost, achieve better fuel economy, power the alternator and maintain a smooth ride. Many foreign and domestic carmakers are using OADs in many of their new models.
Similar to the overrunning alternator pulley (OAP), which has been around for several years, the OAD has a one-way clutch that allows the insides of the alternator to release during engine shutdown and transmission shifting. However, the OAD also has a steel torsion spring that absorbs the increased vibration from smaller, fuel-efficient engines and keeps the belt tensioner still, resulting in a smooth and quiet drive.
The OAD helps to reduce overall belt drive system tension, resulting in lower hub loads on all of the bearings within the system, including the water pump, power steering pump, tensioner pulley, routing idlers and, of course, the alternator bearings. Without the OAD, the vehicle could experience excessive belt flutter, worn or broken tensioners, extreme belt wear, belt ejection, unwanted noise from belt slippage and vibrations that can be heard and felt by the driver.
Although similar, OADs and OAPs are not interchangeable; if a car manufacturer uses an OAD, technicians must replace it with an OAD. Drivers will notice immediately if an OAD is replaced with a regular solid pulley or OAP due to the increased noise, vibration and harshness (NVH). It’s also important to replace an OAD with the OEM-specified replacement part because many are designed and manufactured to provide precise overrun and isolation characteristics for specific vehicle applications.
Because it’s such a critical part of the belt drive system, the OAD should be checked every 50,000 to 60,000 miles, especially on smaller vehicles in warm climates, although OADs can last up to 100,000 miles on larger engines (like a V6) in cooler climates. Failure to replace a worn OAD could result in excessive NVH and unexpected breakdowns. It’s also important to check the OAD if there’s any trouble with the alternator, as the OAD is a wear-sensitive item and is much less expensive to replace.
Fortunately, there’s an easy approach to troubleshooting OADs called the Look, Listen and Feel method. If you suspect the OAD is failing on a vehicle, follow these three easy steps to know for sure:
Look. With the engine running, examine the belt drive system, being careful not to place your hands too close to any moving parts. Take a close look at the tensioner to see if it’s moving back and forth excessively; if it is, the belt drive system probably needs to be serviced.
Listen. Keep the engine running and now listen for belt rumble and identify any belt spans that are vibrating excessively. If you can hear a rumble, the OAD may be the culprit.
To inspect the OAD itself for abnormal noises, put the transmission in Park, rev the engine up to 2,500 to 3,000 rpm, then shut off the ignition. After the engine shuts down, the rotor inside the alternator will continue to spin for a few seconds. At this point, listen for a buzzing noise. If you hear the noise after shutdown, the OAD is likely worn out and needs to be replaced.
Feel. The final test in determining whether an OAD needs to be replaced requires a special OAD tool kit that can be purchased through your warehouse distributor or local tool supplier. Often, this is a five piece kit that includes a 17mm hex, 10mm external hex, Torx, triple square and a 17×20 spline tool.
With your kit in hand, make sure the engine is shut off and the keys are out of the ignition before performing this OAD check procedure. Using a pick tool, remove the one-time-use cap (plastic caps can be removed using a prying motion; rubber and metal caps need to be pierced in the center and then pried off). Based on the particular OAD’s design, insert the correct tool into the shaft of the OAD and—while making sure the belt is tight—rotate the shaft of the OAD in both directions while the belt holds the pulley portion. When the OAD is working properly, it should feel smooth in one direction and have a spring feel in the other (drive) direction. The OAD should be replaced if it’s locked up, free-spinning or rough, or has no spring action.
Once you’ve determined that the OAD needs to be replaced, it’s recommended that the entire belt drive system—belt, belt tensioner and OAD—be serviced at the same time. If a bad OAD has been running on the engine, the belt and belt tensioner are likely to have been negatively affected and may also be close to failure, putting the vehicle at risk for a breakdown.
Understanding OAD technology is critical for shop owners and technicians alike in order to educate customers and ensure full customer satisfaction.
Tom Lee, automotive aftermarket marketing manager for Veyance Technologies, manufacturer of Goodyear Engineered Products, has more than 30 years of experience in the automotive industry. For more information on OADs, visit www.goodyearep.com/OAD or watch OAD video tutorials at www.youtube.com/veyancetechnologies.
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