I noticed one day that the pulley belt was making noise, one of the ribs had separated. I changed the belt checked it after the test run and found that the belt was not running fully on the ac pulley. the ac pulley looks to be in line with the alternator and the crank pullies, after a few times repositioning the belt (sometimes it stays on, mostly its off, only after short in town runs will it stay on.) I reasoned it could possibly be the tensioner pulley bouncing around and allowing enough slack to jump one rib off the ac pulley. Question is, does this happen? does the tensioner even go bad? any help would be great. Oh truck is a 2005 ram 2500 4x4. diesel, of course!

 

Check all your pulleys and idlers, you may have either a bent pulley but more likely a bad bearing on one of the shafts and it is wobbling. Also check that all mounting bolts for accessories are tight and not missing allowing them to move.

 

If belt is running more on one side of tensioner, then it is bad. Get the assembly from advance or other parts store.