Alternator whine problem.

My 92 SL1 had a whining alternator not too long ago (2-3 months). I
took the serpentine belt off and spun it to doublecheck. Sure enough,
it seemed like it had a couple of bad spots on the bearing.
So I bought a rebuild kit, fixed it up and it worked quite nicely for
a little while.
However, the noise seems to have returned. I haven't had the time to
to take the belt off and check it again (just came back from a
business trip and didn't have the tools with me) but I'm wondering if
it is possible that the alternator is acting up again?
If so, any ideas as to what might cause it? (besides a bad bearing in
the rebuild kit)

thanks

Alex

 

Sometimes you have to look at what makes the bearings fail, like an off
balance rotor due to dirt or damage. Maybe even a bent shaft.

If you try to rebuild again, put the rotor on a set of V blocks resting in
the new bearings and if you have a dial indicator, check the run out.

Also try rotating it in to different positions to se if it rolls back to the
same position indicating it is heavy to one side.

 

Oh man... I can't believe I never thought of that.
I happen to have a dial indicator but I'm not sure if I want to go
through the trouble of pulling the alternator out, measuring, putting
it in and then running out to get the parts...then pulling it again...
etc. Getting to it is a pain in itself.
I think I'll just grab one from the wreckers, play with it to make
sure it's ok and take it from there.
Once replaced, I'll play with the old one as per your suggestions to
see what might have gone wrong.

Thanks for the input.

 

While you have the unit apart, change the brushes and polish out the slip
rings.

 

Thanks Opie....

I did that the first time around. Got new brushes, diode pack,
bearings, grease, etc, etc...

Just came back from a junk yard today. Picked one up for $45 and will
try to put it in this weekend.
I still need to replace the front control arms and wheel bearings...
which brings me to another question but I think I'll just create a new
thread for the benefit of others.

 

Oops! I assumed wrong!

Turns out the alternator is working fine, but was able to poke around
with a stethoscope and found the idler wheel grinding and whining.
Unlike the alternator, this at least will be a quick swap (hopefully).

Alex