I just replaced my serp belt yesterday cause I was getting a bad squeal. Now its even worse and I am at a loss. its an 89 4.0. Someone has to have racked their brain with this same problem. I changed the Idler pulley too....

 

are you shore you have the tinsion bolt tight enough if so its probably a pully bearing

 

Make sure the belt is tight. I changed an alternator a couple months ago on my mom's '96 and the belt squealed on startup...turns out I didn't have the belt tight enough. It seemed fine, but it was just loose enough to squeal under load.

You might check all your accessories with the belt off, and make sure they all turn freely. Also clean off all the pulleys. Either soap and water or B12/brake cleaner if you're in a hurry. Just make sure you dry them all off real good.

 

Come to think of it, I felt like I could have tightened it more. Later someone told me to tighten a jeeps belt until it feels like it is going to rip the water pump off, and then tighten it more. everything else seemed to spin free, and with a little drop of water it would quiet down momentarily. I noticed that the belt starts to slip back on one of the pulleys back toward the block as soon as I start it up and thats when I thought I was tightening it too much, so in the AM I'll give her another go 'round. Many thanks, I'll let y'all know how it goes...

 

Just tighten it a little at a time and check for squeal as you go.

 

Have you isolated the source of the squeal?
Have you looked at the harmonic balancer to see if it is seperating and causing the belt to be out of alignment with the adjacent pulleys?

 

went at it again today. Could not get it to stop. Little water and she stopped. My neighbor came out, sprayed a little wd40 on it and it shut up right before slipping off a pulley and eating a 40 dollar hole in my wallet. sweet. Another new belt later, and just like magic, I've got silence....whatever it was, that little gremlin is gone...or more likely just relocated....

 

Belt could've been glazed or just old.

I'd have made the neighbor pay for the belt though...I mean, it was his idea that caused the belt to jump off.

 

Try water pump take the belt off and see if can turn the pully on it. If hard to turn then needs to get replaced

 

Solved this by the way. Harmonic balancer was rubbing the timing cover. Changed it and wohoo no squeel