2001 Caravan Alternator

[sh'maal]

My wife has a 2001 Dodge Caravan with the 3.3 L engine. It started making a low pitch squeel noise on start up that goes away after 4 or 5 sec. When the engine stops there is a highr pitch squeel for 1 -2 sec after the engine stops. I looked under the hood and the alternator rotor continues to turn after the engine stops and is the source of the second squeel.
It seems the alternator has some sort of clutch on it that allows the rotor to turn after the drive belt stops. I've never noticed this noise before and suspect it is related to the initial noise. Electrically everything is sound - no idiot lights. The parts store don't stock this alternator so I'll try the dealer tomorrow.
It turns freely by hand (no apparent bearing problem). When it is turned by hand, then stopped, the clutch disengages and the rotor still turns one revolution. Has anyone had any experience or problems with this type of alternator?
Any advise is appreciated

[sellinghomes4u]

There is no clutch on the alternator. Sounds like you need a new belt & tensioner. THe only thing with a clutch is the a/c compressor.
Larry

[sh'maal]

I believe clutch is the right term (I'm not a mech engineer). It works like a ratchet only without the pawl noise. I have the removed one in my hand and the new one from the dealer. Apparently the clutch is why these do not exist on the rebuilt market. It does not seem to be sophisticated enough to be viscuous or centrifugal, it's probably just friction. When the engine is turning the alternator clutch is engaged and the alternator turns. When the engine stops the clutch disengages and the rotor coasts to a stop. My guess is the clutch is used to either unload the belt and prevent it from snapping from the alternator rotor inertia or the rotor has plastic parts that snap off if stopped suddenly. If it was my design I'd consider a ratchet type affair but it may be too noisy or not wear well. If you look on the front of the pulley you'll see a lead damper inside a race.
Autozone wants $384 and doesn't stock them and O'Reilly wants $155 and also doesn't stock them. Both are puzzled but received no help when they called the home office. The dealer charged me $255. There is a noticeable difference in the amount of dampening that occurs between the new and the old. Both my start up and stop squeeling have stopped. I'm certain that the stop squeeling was from the alternator (I could see the rotor still turning) but was unsure about the start.
It was a pain to to move the auto belt tensioner to get the belt off. I suspect there is a special tool. There is a hole that fits a 1/2 inch drive on the idler (long arm) side but the 2" clearance precludes getting a rachet or a breaker in. I ended up using a 22mm combo wrench on the short arm side and skinned my knuckles moving it to get sufficient slack to move the belt on and off.

[AMD Rules]

This is an interesting topic. I did not realize that there was a 'clutch' on the new alternators. After reading your reply, I decided to review the FSM to learn more about how they work:

Excerpts from the '04 FSM:

GENERATOR DECOUPLER PULLEY
DESCRIPTION
The Generator Decoupler is a one way clutch (Fig.
3). It is attached to the generator and replaces the
standard pulley. It is a non-serviceable item and is to
be replaced as an assembly. It is a dry operation (no
grease or lubricants). The operation of it is not temperature
sensitive and has a low sensitivity to electrical
load.
OPERATION
The generator decoupler is a one way clutch and
should be replaced as an assembly. It is designed to
help reduce belt tension fluctuation, reduce fatigue
loads, improve belt life, reduce hubloads on components,
and reduce noise.

It is ironic and unfortunate that an item meant to reduce noise, is creating an unwanted noise for you.
Your problem is listed in the troubleshooting section, for which you have already properly identified:

CONDITION
Noise from generator at engine shut down.
VERIFICATION PROCEDURE
1. Start engine and allow engine to idle.
2. Shutdown engine and listen to generator.
3. Noise heard just as engine stops. Sounds like a click.
4. Remove accessory drive belt.
5. Verify rotation in counterclock wise direction is rough.
POSSIBLE CAUSES
Defective decoupler pulley bearing.
CORRECTION
Replace decoupler pulley.

The decoupler pulley needs to be torqued to 81 ft-lb.

Thanks for letting us know how you solved this squeel.

[DSMLVR]

Great postings. You learn something new everyday.

[Al Steadman]

If you want to learn more about this product there is a great write up at this site. http://www.tendeco.com/website/decou...ecouplers.html

Goodyear actually offers this part in their product lineup. It can be purchased without having to buy the entire alternator.

[Hokiefyd]

That's great! I always wondered why the alternator pulley on ours extended out another 1" beyond where the belt rides. Great info!

[05SXT]

Looks good on paper but it's just something else to go wrong...

[IAfarmer]

My 2002, along with a 2002 at work had a recall for the alternator. I was having the very same problem and the alternator was replaced for free.

Anyone else remember that?