This is kind of a newbie question, I know, but I want to be sure before I buy a new alt.

A few days ago I noticed a fairly loud whine coming from under the hood when I was driving. The whine gets loud at higher RPMs. Checking my guages, I noticed my voltage had dropped from around 13 to closer to 11.5. Over the next couple days I drove it a couple times and the voltage has since dropped to around 9. Last night when I parked it, my gauges were going dim and such.

I assume my alternator is just about toast, but I wanted to check with you folks before I bought a whole new one. I thought it could be the serp belt, but it seems tight still. Is it possible that it could be slipping enough to drop the voltage but not enough to be able to see from looking at it?

Any information would be greatly appreciated. Does it sound like I need to just buy a new alt or are there other things I should try first? Is there a rebuild kit or something I should use?

The car is a '91 Firebird with 75K miles (probably original alt).

Sorry for typing so much for a simple problem. Thanks for your time!

 

If your voltage is dropping like that.....yeah, I'd say bad alt alright. Your system needs roughly 12 volts JUST to stay even and not drain the battery excessively. Less than 12 means your electrical system is relying entirely on your battery to supply the remainder of the necessary power.

If your belt was slipping bad enough to make your alt act up....you would know it. Replace it. Might consider upgrading to a slightly larger one too, if you have any plans for stereo, etc. in the future.

 

Yep alternator is most likely toast. The whining you were here was the alternator I dont remember what causes the whining but I would say that theres a 99.9% that its your alternator.

 

Yes, if your voltage is dropping like that, your alternator is history. It's an easy replacement, go for it. Just use the right tools and don't round-off any bolt heads or nuts.

Disconnect the battery first!!!

What you are describing has happened to me. One time the alt failed it was making wierd noises then the front bearing totally failed and the shaft cocked over to the side from belt tension and the fan was grinding on the bracket. Ouch!

Another time it failed I was 2 hours drive from home. Made it on the battery with everything shut off. I was down to about 9 volts when I finally got home. This is real hard on the battery and is not recommended. Since you have already hammered your battery, you might want to throw it on a charger for an hour or so before you try to restart the car with the new alternator.

 

Thank you all so much for the replies. I'm going to go grab a new one right now.

Thanks!

 

I'll second that! Charging up a flat battery with an alternator is a good way to toast a fresh alternator. If you're stranded on the road, and have to take a jump to get started, that's one thing, but if it's at all avoidable, don't let your alternator charge your battery from a deep discharge.

I had replaced an alternator on a tractor once after noticing the voltage gauge was low. I don't know how long that alternator had been bad (tractor still started on it's own, without a jump), but after about a half hour, that alternator smelled like burnt electrical, and the outer casing was over 212*. Messed it up pretty good.