C5 alternator question

I had to replace the alternator on my 2001 and discovered there are two versions of alternator. One for auto trans and one for manual. The AT alternator has a clutch, the MT does not. Basically, what/why? What
does the clutch do and why does it make a difference? Mine is an AT version.
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Millions of vehicles are now factory-equipped with an Overrunning Alternator Decoupler (OAD) rather than a conventional solid pulley or one-way clutch pulley. A failure to install the correct replacement design could cause severe damage to a vehicle's belt drive system.
An OAD Decoupler is similar in appearance to other pulley designs but plays a vital role in synchronizing the belt drive system. When replacing an OAD-equipped alternator, the only acceptable choice is another OAD unit.
Many new vehicle accessory drives are realizing a 1.5% to 2% fuel economy improvement with an OAD. These improvements are possible by utilizing a Lean System design philosophy. Lean systems can significantly reduce the common parasitic losses found in accessory drives, due to the belt bending that occurs during operation. The parasitic loss reduction is a result of a holistic approach to accessory drive - drive layout, OAD, and tensioner design/matching.
Couldn't have said it better myself, we all know that. ;-))
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On 7/10/2012 3:42 PM, Dad wrote:

Nicely cut. Any idea why the manual doesn't use the same system?
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Snap and sharp lag, you know, like how you tear out a CLUTCH.
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By the way the pulley number is Goodyear 49908 and cost $90 and if it fails your alternator will not charge but does not need to be replaced. No need for a $360 alternator with a new clutch.
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