Deep Knocking sound/ Alternator

[BlackOut89]

Ok my alternator went out a while ago and i got a new stock one from a friend in the Buick club where i live. This new alternator had a smaller pully on it so when i put it on i used a smaller belt. After awhile i started to hear this deep knocking sound. we thought maybe that the belt was to tight, so i took the belt off and ran the car and the knocking went away. So what i did was take the old pully off my old one which was bigger and put it on my new alternator. Slapped another new belt on and the sound came back I dont know if its the alternator itself or maybe my tensioner?? idk..help

 

[asloan5]

could it be the tensioner bouncing against the stop (the maximum travel) ? if the pulley is not true the it was cause the tensioner to make a racket also.

 

[BIGPSI]

take a screwdriver and put it to your ear and the metal end on the alternator. it works like a stethoscope. if it makes alot of noise you found the problem.

 

[ryan319]

mine does the same thing. i put a piece of wood (qtr round trim) between the alternator and my ear (like a stethoscope) to confirm where the noise was coming from.

if you come up with a fix let me know what it is. once i confirmed it was the alternator i never really worried about it. i'll deal with it if/when it breaks.

 

[BlackOut89]

Sorry it took me so long to reply back, i fixed the problem. It was my alternator, the front bearing was shot, so i replaced that and while i was at it i went ahead and replaced the brushes...knocking gone thanks guys