Hello,
I have an issue with a serpentine belt that keeps breaking on a 1995 GMC Sonoma. The new belt goes on well however where it wraps around the bottom pulley that is directly bolted onto the end of the crankshaft it is slightly running off to the side of that pulley by one groove. This create rubbing on the Inside Edge of the belt and eventually destroys it. The pulley does not seem loose I'm wondering what the remedy or fixes to this problem are ? Can anyone point me in the right direction. It appears that that pulley is sitting too low and needs to get shimmed back up?

Did you check to see if the other pulleys are tight and not loose or wobbling and in proper alignment with the crank pulley?
The pulley that "feeds" the crank pulley may have bad bearing causing it to run at an angle instead of parallel to crank pulley.
Unless the thing has been messed with I highly doubt the crank pulley needs shimming.

I think a buddy or mine had the same issue on his GMC and that there was a recall or remedy notice for it. I do remember he pulled off a plastic debris cover on fan because he had to replace the belt so often.

I would think that the culprit is the one before the crank shaft pulley. If it was that one, the crankshaft would have moved and then a busted belt would be the least of your problems. Check the idler and tensioner pulleys for play in the bearings.

Usually the culprit in my experience as well. Did just have a power steering pulley come apart on my Father in laws truck. Check them all for play.

i had a 98 dodge caravan that was so bad they made a double sided belt for it

all new pullies and a belt with notches on both sides

if not hit a puddle and there went your belt that was around 150K went a little over 220K but on it's 3rd set of heads

When I was in the dealership, GM was pushing the pwr steering pulleys on too deeply. Generally caused a belt noise but supposed it could cause your issue if severe enough. If the shaft protrudes past instead of flush with the pulley hub, the pulley needs to be pulled out flush.

Just a stretch, but hear me out. Is this Sonoma a manual trans? Reason being, is with lots of miles, if a 4.3 they are capable of very high miles. Crankshaft thrust bearing gets worn from pushing clutch and shifting gears, that would push crank forward, perhaps enough to jump a rib on belt. Other wise the normal suspects of a damaged pulley, tensioner/bearing, mis positioned pulley as mentioned above. Does tensioner spring allow movement without catching? Try releasing it remove belt and see if it will rebound. They are kinda cheap on Rock Auto.

You could also have the wrong width belt, seen that many times.

I'd go with the tensioner being whacked out before the crank does anything though.

I'd also back track a bit and try and remember what cause the first belt change, if you never changed the tensioner then it's probably just gotten worse.

I had a wrong belt twice in a row on my expedition that I was about ready to shoot the auto parts guy, so been there with the wrong width !

The first thing I would check is the belt tensioner. Make sure the bearing are good and where it bolts to block its not loose.

Thanks for insights...it's a manual with 93k miles
Will check tensioner and other pulleys for play.

All good info here, all also pretty easy checks. Now that you said it was a manual trans, rpm's vary quickly and often while shifting. Have someone push clutch in and out while watching crankshaft and belt close, if you see movement, not good. I know a long shot, but in all my years of transmission work I have seen enough of this. I saw a few cases where oil pressure dropped at idle when clutch pushed in v/s released. Long shot, sure but all good info and mostly quick items. Betting on stuck rusted tensioner spring. A tip when putting tensioner on, with new belt is to run for a minute, shut down and mark moving part of tensioner with fixed part. This shows exactly how much wear and stretch serp. belt has over time. Paint stick works, as does deep scratch.

Had a Rendezvous that the dampener pulley on the crank started working loose. It was a two piece with an inner outer held together with rubber. When the rubber broke down the outer shifted forward causing misalignment and belt breakage.

Ok, trapper mechanics ...
I just put on a new belt tensioner and I'm having the same problem. I checked all the idlers and they are all very straight and appear to be in line. However on the fan where the belt wraps around it there is a decent Groove in that housing. Belt is correct size. As soon as you started it jumps over off of that one groove on the main crank pulley. So we shut her down and I take the tension off about maybe 1/2 inch and it snaps back into place where it should be. I know this isn't rocket science it's just a fan belt and where is Shoe something's not lining up or is out of whack

Pic is looking down onto the crank pulley

That's the dampener I speak of. GM makes the crank/dampener pulley as a two piece unit with a rubber "dampener" sandwiched in between. When the rubber breaks down the outer slides forward. The whole pulley unit will need replaced.

Could the crank pullly be on to far. Could it be moved just 1/16th of an inch out or in whichever it needs. I am not a mechanic

Quote<I know this isn't rocket science it's just a fan belt and where is Shoe something's not lining up or is out of whack>quote

Something IS out of whack. Look VERY closely , something is out of whack. Belts do NOT like anything out of whack. Period.
Crank pulley is about the only thing that is not out of whack (generally)
Something is not right. I can't tell just from some pictures , sorry.
Look everything very, very closely , even ilder pulley tension can be an issue. The slightest thing can cause things to get out of whack. Double check you have the right belt , even.
Something is not perfect. That is the key. Wish I was there to see it in person.
Everything HAS to be perfect , that is the key. Something is not perfect.

You stated , fan belt has a groove in the housing , it that also the water pump ? I would look there very closely.

Year , make, model and engine size helps for diagnosis for us Tman mechanics. Please give us the info ,thanks.

Take the belt off then check each pulley for play. You have a bearing out or something has come loose.

I think it's the balancer behind the crank pulley...we have replaced all parts except that one.. ..on this
95 gmc sonoma, 4 .3 liter manual transmission.