Correct alt. pulley diam. & where? - God awful noise!

[Mike Pope]

Hi.

I recently replaced the alternator on my wife's suburban with a "new" (not reman) one from Auto Zone....one of their "Duralast Gold" models. (Actually was replacing a replacement under warranty) Anyway, after replacing it there is some sort of really wierd rattle type noise at idle only. As soon as rpm's increase, noise goes away. Noise will almost go away if no load on belt......if you put an electrical load on it by turning on fans it gets worse.......if you put your foot on the brake, it gets worse........when you turn on the A/C, it initially goes away (increased rpm's) then returns. I don't drive the Suburban, but my wife said she'd never heard it sound like that before. It's pretty loud..............3 out of 4 people at a stoplight turn their head trying to figure out what that god-awful racket is! :D So I figure it's something wrong with the alternator, and return it for another............SAME PROBLEM. The belt is new, so that's not the problem......no squeeling/whining etc., tensioner feels to be doing it's job, tensioner pulley is new. If I remove the belt and start the engine, noise is gone. All pulleys that can be spun by hand feel ok. SO, I do some reading on here and find out that pulley diameter on replacement alternators is sometimes wrong...........could that be the problem? I did a search on here and have found 2 different answers.......one said 62mm or 2.44", the other said 2.6", measured at the widest point (lip). I can't measure my other one, because it went back for "core." My current one measures about 2.44" at WIDEST POINT.

Is this right? Any ideas about the noise? I realize it may not even be related to the alternator, but want to at least find out if I have the right pulley.

Thanks for any help!

[Mike Pope]

OK, me again...........upon further search and inspection, I think the noise may be from the crank pulley........sounds like others have had similar symptoms and it turned out to be that.....

I would still like to know if I have the right size alternator pulley, though!

Thanks again.

[WhiteGMC]

Mike,
Check your vibration damper...also the pulley attached with 4 bolts on the front of it. It is mounted in rubber and it goes bad and makes a lot of noise. Look up from under the car and you will see this pulley...look for a crack around the outside. Good Luck!

Jerry

[Hye]

The pulley on the end of the crankshaft is held in place by four hex head bolts. Their heads should be centered equidistant from the four spokes of the pulley. When the rubber that helps dampen vibrations breaks down, the screw heads hit the spokes and rattle as you described. Another quick check is to see if the heads are centered between the spokes. If not, the part is bad. It should be replaced. I've heard that if you let this go on too long, you might loose a crankshaft. On my 1994 its P/N12557345 and it will set you back a bundle.

My alternator pulley is 2.57" O.D. The smaller pulley you got from AZ might make the tach read high. An alternator repair shop can supply the correct pulley.