Jeep threw a belt

97 XJ 4.0L Auto 4x4

My Jeep threw it's belt 2 weeks ago, got chewed up in the mechanical fan, and tangled between the fan clutch and radiator. This caused the radiator to pop and I had to order a new one.

Question is, what all should I check to see why the belt was thrown? I will inspect the pulleys and make sure that they are good, but I am assuming the belt just got old and stretched in the extreme southern heat. I was planning on replacing the belt since it was 6-7 years old, but just never got around to it.

Just look for any debris wrapped up behind any of the pulleys--use a bright light for the inspection.

Spin all of the belt-driven accessories and idlers to check the condition of their bearings/bushings.

Check the condition of your harmonic balancer (crank pulley). Other than a seized pulley elsewhere the HB can begin to separate and one half of it walks in or out and gets out of line with the plane of the other pulleys.

If it looks like the one in the picture...it's starting to go. Whether that's what caused your problem or not...I dunno. A messed up HB can also walk the other way and wear a hole in your timing cover.



The outer part is held to the inner part with a rubber "seal". If the rubber seal deteriorates. the two halves separate...and that's bad.

I hope the balancer isn't bad because it was replaced about 3 years ago.

check the water pump and idler pullys for play, those are the 2 most common culprits

I changed out a wobbly water pump in a co-worker's '00 last night that threw the belt into the mech fan. It took 5m just to cut and untangle the belt. Now if I can find the 8mm socket that it ate. . .

I've found nuts/sockets stuck behind the WP pulley, just on top of the HB...this after 2 years if driving. Don't know if it contributed to my WP going south, but it likely didn't help...I got it out with a magnet.

Well I got the new radiator in and the new belt. I put the belt on first and fired the Jeep up for a brief few seconds to watch all the pulleys spin just incase and everything seemed fine. I felt each pulley and they all seemed solid. The amount I had to adjust the pulley out to get the new belt on, really showed me how much that belt had stretched over the years. So everything is good now. Temps from the new Champion 3 row radiator is great! This is the same one I had before and the performance was awesome! Thanks for all the help guys!

my experience was i couldn't stop the belt chirping found it was a idler pulley that had worn and the running surface was no longer parallel to the axis

so the belt would try to run off only to be pulled back by the next pulley with the accompanying chirp

just about drove me insane trying to find it

Ewenm said:

my experience was i couldn't stop the belt chirping found it was a idler pulley that had worn and the running surface was no longer parallel to the axis

so the belt would try to run off only to be pulled back by the next pulley with the accompanying chirp

just about drove me insane trying to find it

Click to expand...

I love that, I had the same thing some months ago, I was convinced it was the water pump... put in a new water pump, put it all together... CHIRP CHIRP CHIRP AAAAAHHHHHH!!!!!

More oddly still, this was in the dead of winter, but I dutifully took out the pressure washer, hooked it up to hot water, and blasted everything clean with boiling water and purple power. So at least I didn't get covered in grease fighting with everything. At the same time it was so cold the overspray turned to ice and I couldn't figure out why my tools kept sliding off until I took my gloves off and was like "oh, derp".

But $12.99 later I had a new pulley installed. I've since figured out which mcmaster-carr part number I needed and bought 5 more bearings so I punch out the old bearings, and I always have a live spare.

That aside, +1 on whoever mentioned the harmonic balancer, if it's even suspected I would recommend replacement, they're relatively cheap ~$40 and they're sort of easy to replace. But it's a lot easier to deal with a "scheduled" replacement than it is dealing with one that's thrown it's rubber somewhere on the highway.