I have a sort of rhythmic thrum in my 2005 Chrysler Town and Country 3.3L which gets more noticeable with a load on it, like A/C. I was told it was an alternator going bad and would get worse, which it seems to have done. I also heard it could be just an alternator decoupler pulley, of a tensioner or idler pulley. How do I know which it is and how do I change the whole alternator if I need to? I have found directions for all the pulleys replacement.
Hi Carol, You might be able to locate the source of the 'thrum' by means of an 'ear horn'. That is essentially taking a piece of rubber hose and holding one end at your ear and then the other end very near to each suspected rotating item to determine which has the loudest apparent sound source. Just like a physician uses a stethiscope but don't put the free end in contact with the moving part. The decoupler pulley is a device on the alternator shaft, instead of the typical belt pulley, which is designed to make for quieter and more efficient operation by only driving the alternator in one direction (slips in the reverse rotational direction). I am not certain whether you can tell if that decoupler is the source of the noise or the bearings inside the alternator proper, but the 'ear horn' might help you to differentiate those two locations. If it were just the decoupler pulley then you would not have to remove the alternator to replace it, but it does require a special removal tool made by Miller Mfg. Co. which makes such tools for Chrysler products. On the other hand, if it sounded like the alternator bearings and not the decoupler pulley, then you would remove the alternator and ideally take it to a shop that rebuilds alternators where they would remove the pulley using their tool and also evaluate whether the pulley is alright or needs to be replaced. You could call around to alternator/starter shops/rebuilders to see if that is not the case. I can copy several pages showing the alternator/pulley r & r from the '05 shop manual I have on a CD and attach them to an email which I would send directly. To do that, I need to know your email address which you would tell me by asking a NEW question, only this time click on the box to make it PRIVATE. Then in the text area of the question tell me the address. I am not privy routinely to the questioners' email address so you have to go through this approach to tell me it. Please 'rate' my answer (see below). Thanks, Roland