What does it sound like when your alternator is on the way out ?
 

My alternator (71T) is making some weird noises at idle - it is especially noticable when the car is cold and the idle hasn't evened out. I suppose it sounds somewhat like a 'knock', but its not a low down rumbling sound, but more of a jolly mid-tone sound. It will go 'hump-de-bump-bump' and go silent for a while, then do it again. It is very odd. I know these things are hard to diagnose via e-mail, and I'm sorry for the poor description of a mechanical noise. Does anyone have any ideas ?

Are these things rebuildable, or should I just shell out the cash for a new one?

Thanks.

My car makes a similar low down rumbling noise. I was told it might be the alternator bearings. There are several posts about rebuilding alternators and replacing bearings. Try doing a search of this site. I just got an email from a guy on this site who had his rebuilt for around $100.

David

Try taking off the fan belt and turning the alternator by hand. It should be smooth and even feeling.

I had my alternator rebuilt, new bearings, brushes, and some frayed internal wiring repaired for $105.



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Bill Krause
'79 911SC Euro

Almost sounds like a loose A/C belt or Alt. belt setting up a low vibration. Look at the belts when it's thrumming & see if they're vibrating when you hear the sound. My Volvo does it with the AC belt, but I don't want to overtighten it for fear of ruining the bearings.
regards,
jlex.

you can use a long screwdriver as a stethoscope. hold the handle up tight against your earbone and touch the tip to the alternator housing. if you have a bad bearing you will hear it rumble. works for tensioner noise among other things. dont get your hair sucked into the fan. i throw this in because i tend to be a bit long haired. must have been my hippy days.

If I take the belt off mine and spin it, it has 2 or 3 "rough" spots. I'm not sure what else you'd call them. They're spots that are rough enough to make a faint clicking sound--even when hand spun. I imagine it's more when the car is running. What the hell, as long as I can start my car, it doesn't run hot, and I'm not losing charge, I'll defer the rebuild or replacement.
Hope that's not a mistake.


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Kurt B
'84 Carrera Cab.
carrera_cabriolet@yahoo.com