Needs to be posted in the auto section.
Threads are stripped or bearing is disintegrating.
Depends on which car and which belts.
Tighten the belts
The 1989 Toyota Corolla serpentine belt can be tightened or loosen with the tensioner pulley. Pry to the left on the tensioner pulley until the belt is tight. Tighten the tensioner pulley.
There is a Tensioner Pulley that you have adjust in order to tighten the belt. There is another hex bolt that can be screwed in or out depending on how you want to tighten or losen the belts. Adjust it until prefered tension is reached.
Your idler should keep the belts tight. I've had to change my tension idler on my 1997 gtp
Loosen the belts, unbolt the old alternator, bolt the new one on, tighten the belts back up.
1989
You must hand tighten the filter.
By replacing the belt tensioner, this is a serpentine belt systems there is no adjusting the alternator bolt tighten the drive belts, if the belts are loose you must replace the belt tensioner and the belt to retain optimum performance from you Charging sytem as well as you other equipment being driven by the belt system.
You can't.
When changing belts, it is important to know the layout and have a diagram to help guide the removal and replacement of these belts. A diagram for these belts can be found in the maintenance manual of a 1989 Toyota Corolla 4-A-F.