Slow Shredding of serpentine belt

This has slowly gotten worse, so I thought I'd post about it and see if anyone has any thoughts or similar experiences.

On our 2007 3.7L automatic 4x4 KJ, the apparently OEM (Still has pentastar IIRC and the OEM PN) belt developed minor chunking at the edge/side on the back (smooth) side. I noticed this somewhere around 20-25k. (We bought with something like 16k Aug 31, 2008 and are about to turn 31k.)

It's gotten worse, to where fiber is starting to poke out a little bit.

I did new plugs and air filter last night, so I also took the time to look over all pulles. I looked over the AC, PS, idler, tensioner and alt. pulleys visually and rubbed my finger over them. I also felt all the way around the crank pulley.

One with an apparent odd surface was at a seam in the steel PS pulley. But that seam continues across the ribs and the sides of the belt don't touch the pulley in a way that it would cut into the sides of the back of the belt.

Another odd surface is the water pump pulley that has developed small bumps more towards the front of the vehicle. Sandpaper didn't take these down fully. But again, I'm not seeing how those would cut into the sides of the belt and not the backside of it.

My focus on this is not due to being able to buy a belt every 30k. It's that I'd like an expensive repair (AC comp. for example) done under warranty if appropriate.

And especially this: the ribs of the belt are uncracked, have flat faces at their peaks still and are not heavily worn.

I've done a little bit of searching on this topic in the past and today but didn't run into threads that covered this.

Thoughts on how to further troubleshoot?

The only things I can think of to check is where the back of the belt contacts any of the pulleys (which it sounds like you have done) and make sure that there is correct play in the belt. In case you don't know how to do that take a straight edge and put it across two pulleys and mesure the distance you can deflect the belt. It could be that the belt is too tight, and is putting too much stress on the fiber backbone of the belt.

Have you replaced your belt tensioner/pulley assembly? I doubt it at 31k... But had to ask.

If the tension isn't right on the belt it could be flapping around a bit under acceleration, and that might be causing some wear. Used to see that all the time on other vehicles i have owned, usually replacing the belt and tension took care of it. I haven't had to on my KJ yet.

Odd problem... I would do what he suggesting and take a long metal ruler and check that all the pulleys are aligned. If one of the accessories with a grooved pulley is slightly shifted to one side it might have the pulley at a slight angle to the belt and that would rub the heck out of it too.

Ever had anything replaced, alternator, AC, PS Pump?

Would replace belt,probably tensioner also.Could be just a sorry belt.

I change my belt and tensioner every 30,000miles just because,it's cheap insurance.

Oh and the cut in the PS pump pulley is supposed to be there,it's for heat expansion due to the pulley being plastic.

I went on vacation; thanks for the help in my thread.

Nothing has been replaced AFAIK. (we bought @ just under 16k miles)

The tensioner felt very appropriate in tension against my 1.5ft breaker bar. It definitely didn't feel undertensioned.

I will go over the pulley fore-aft alignment. As well as the deflection of the belt vs. straight-edge.

Now I wish I would have checked mileage on our trip after the plug change.

Awww KJ said:

I went on vacation; thanks for the help in my thread.

Nothing has been replaced AFAIK. (we bought @ just under 16k miles)

The tensioner felt very appropriate in tension against my 1.5ft breaker bar. It definitely didn't feel undertensioned.

I will go over the pulley fore-aft alignment. As well as the deflection of the belt vs. straight-edge.

Now I wish I would have checked mileage on our trip after the plug change.

Click to expand...

There are marks on tensioner that indicate wear in it,should be less than 1.25in I believe,check FSM or haynes for certion

When we took it in just prior to end of warranty, I asked for them to look at the pulleys since the belt was in good shape except for the sides. They replaced the belt free. It has not shredded since (in 5000 mi.)

When does your warranty expire?
You should keep an eye on the new belt. Anything that it passes over may have caused to wear out prematurely. When my belt failed so did the tensioner & the water pump. It's hard to say what failed first.

Myself I carry a spare belt just for insurance.