This is puzzling. The battery is good,the alternator checked okay,belt tension okay but when I make a turn or turn on the headlights the alternator belt starts screeching. The volts also drop
down to 12V when the headlights are on. Overload?

 

If the belt is not too tight/loose it could be the alternator going out.

 

I've been having on-going problems with my dual alternator belt. Kept having to replace them cause they were screeching. This time with them going out, the screeching is really bad at night when I have lights and the heater running.

Turns out that my water pump is going out. I found out because I was consistently loosing a little bit a coolant at a time through the weep hole. I have a new water pump waiting to go on.

 

The alternator was checked and the water pump is okay

 

How was it checked? I've known of a few bad alternators that were checked and passed. It could be that you have a bearing going out in the alt.

 

It was checked at an alternator shop but I swapped in a friends alternator and it did the same thing.

 

Well if its not the alternator I would check to see if its the belt. Is the belt worn? Is there any grease or oil on the contact end?

Also are you sure that the turning and the screeching isn't another problem? Do you have power steering? Have you checked that belt if you do?

 

my first question would be how old is the belt? the nex question would be are you sure the belt is the proper length?

 

Are you running a belt over your airpump? If not there won't be enough tension on the water pump pulley and the alternator belt will fail.

 

is there a Spacer on the Long bolt that you Install the alternator On?
where did you PLACE it?..if it is on the FRONT you are Wrong.It needs to go to the Back of the alternator,inbetween the alternator and the bracket.
the front bracket of the Engine must Touch on the Ear of the Front of the alternator..
I am saying this,because I think you have the belts misaligned due to the Spacer not being installed incorrectly.That would cause a Squeal,snapping belts,etc.

 

the car has all new OEM belts, all properly alligned and clean. S5's have no spacer. It will only screech when there is a load such as headlights on. Even making turns will give off a screech.

 

Are you sure your belts are tight enough?

 

The belt tension is fine.

 

screeching means two things. bent pulley or loose belt. figuring out the first may lead to screaming in your case.

 

What is the deflection between the alt and the main pully? 1/2 inch, 1 inch?

Remember the deflection has to be set and correct. You can not just crank the alt up until the belt "feels" tight.

 

its your alternator. i had the same problem not to long ago. just replace it and i bet your problem will be solved.

 

The deflection is about 3/4" . There is no problem if all accesories are off,drives fine. With the car parked,at idle ,headlights on it's okay until you rev it past 900 rpm then it starts screeching.
I swapped in my friends alternator and it did the same thing.

 

if it doesn't end up being the deflection then for some reason i feel as the bearings may be failing on one of your pulleys, maybe not the alternator one.
could be a power steering pulley bearing or something that may be off.
just a guess though.
good luck with your mystery.

 

Disconnect all the belts, and just rev it. If there no noise, then check each pully.

 

Strange, I painted the pulley and it's been fine so far.

 

haha, nice.