Noisy belt with headlamps

[ADRay]

Any ideas why my belt screeches like a bat out of hell when I turn on my headlamps? Usually only when starting off and stops when I'm up to speed in 4th. Not a new problem since the alternator replacement.

[MPlayle]

Turning on the headlights adds to the load on the alternator, increasing the effort needed to turn it.  The belt may need just a bit more tension to not slip due to the increased effort needed by the alternator.  You may also need to clean/scuff the alternator pulley as it has possibly glazed as well.

Make note of the current position of the belt adjuster(s).  Loosen the belt enough to hand spin the pulley.  put some brake cleaner on a rag and rub in the groove of the pulley while hand turning it to clean the pulley.  Retighten the belt to the original position or just a fraction tighter.

[94touring]

Yeah tighten it up.

[Dan Moffet]

Check the belt for glazing (shiny) or cracking. If your belt has stretched or is wearing out, it is time to replace it. Clean all the pulleys if you can. Make sure the water pump and alternator (or generator) turn freely - a seizing bearing can wreak havoc.

Don't over-tighten a belt or it will break some dark night. It should have some flex (about 1/4") when pressed firmly at it longest span between pulleys.

In the "old days" when V-belts were common, you could get belt dressing (a bit like ski wax) which improved grip. An old trick to quickly quiet a noisy belt was a couple of drops of auto transmission fluid, conveniently applied from the transmission dipstick. 

[ADRay]

thanks everyone for the suggestions.

Oddly enough, the last two mornings I've headed out early and flipped on the headlights - no screeching.

Sometimes all you have to do is complain.

[MPlayle]

Something may have gotten on the belt or a pulley that was letting the belt slip and it has now worn off?