Alternator decoupler pulley

[d215]

2003 Boxster S 22000 miles

I seemed to have located the source of the howl from my drive belt system. The "decoupler" pulley is my best guess. All of the bearings in the system seem smooth and wobble free but despite the smooth alternator feel when it is driven it seems to be the source. Has anyone had a similiar situation?

Edited March 30, 2008 by d215

[RFM]

This occurs occasionally rather uncommon, have you tried with a new belt already?

[d215]

This occurs occasionally rather uncommon, have you tried with a new belt already?

Yes I have put on a new belt because that was my first suspicion. The alternator itself is smooth as are all of the idlers. Since the alt. is noisy I think that is all that remains. I have not rmoved the plastic cover on the pulley to see what is involved in replacing the pulley.

Does anyone have any helpful tips?

[wvicary]

I would very much doubt this is the source of your noise, any chance you could post a sound clip? A failing diode in the alternator can cause noise but I have never seen the decoupler fail.

[Tool Pants]

How were you able to isolate the noise as coming from the alternator?

[d215]

I finally got around to puting my '03 back together. The diode array seemes good based on a ripple test done at the battery (since it is near impossible to get at the B+ terminal on the alternator). The decoupler pulley when removed showed signs of rubbing on the face of the alternator housing as a result of axial play. I too, replaced a lower idler pulley as it was a little loose. I obtained a Gates decoupler from Rock Auto and got a Porsche OEM idler from Pelican. All in all it was a reltively easy but time consuming repair and most importantly the noise is gone.