"FBNE" > wrote in message
...
>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.

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. ;-))