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I have a 2006 and I did not have a decoupler. I think they came in like around 2010 or so. The decoupler is used when you back off throttle (thus helping with belt whiplash) it kind of free spins like a torque converter.
For my 2011, the sales information for the GM ACDelco alternator P/N: 25888970 states that this alternator is used on both automatic and manual transmission cars (no difference)
What is the purpose of the decoupler pulley on the alternator?
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.
My C5 A4 has it, but the pulley looks much smaller than the one in the pic, unless it's an optical illusion (or fading memory)! I believe it helps with the serpentine belt chirping when the next gear engages. Never had one apart, so IDK if it works like a sprag clutch, or not.....
Alternator decoupler
)! I believe it helps with the serpentine belt chirping when the next gear engages. Never had one apart, so IDK if it works like a sprag clutch, or not.....
