Serpentine belt keeps destroying forward rib

[SubstanceP302]

Just purchased a 1025A2 last week and I have a long list of items to work through.

The current issue I’m having is with a serpentine belt. The first belt ate itself the 3rd day of driving. It shaved the forward rib partially off and the tail hacked up one of the coolant hoses. All the pulleys spun freely, and the tensioner certainly had plenty of tension. I do not have an AC system.

I replaced the ~98” belt with a Gates Micro-V K080981 (which I believe is 98 3/4”. I had to use a breaker bar to take 100% of the tension off in order to barely get the new belt on. (which makes me worry the belt was a little too short.).

after reading several other threads, I checked all of the pulleys to make sure the belt was properly aligned. The truck ran fine for the better part of the week, then last night started shaving the front rib off just like before.

this morning, I inspected the whole system and watched it run. It appears the belt is slipping forward on the crankshaft pulley when the motor is under load. Sometimes when the truck is idling or off, it will slip back on to the correct grooves. When I increase revs, it pops forward a rib.

The tensioner is also moving back-and-forth quite violently. This might just be a function of the fact the belt is missing half of the front rib. The oscillations of the tensioner seem to match up with every time that tear in the belt hits the crankshaft pulley.

The crankshaft pulley does not appear to be wobbling or out of alignment, but something is causing the belt to slip forward a rib when revs increase.

i’ve read some other threads, but they all have the opposite problem where the belt is shredding itself on the cab side.

Any thoughts?

I can’t find anybody in the Charleston area who’s willing to work on a HMMWV, so I really have no choice but to figure this out myself.

 

[TOBASH]

Look for a cracked bolt or a loose bolt or incomplete or broken brackets. Use a straight edge to make sure everything is either parallel and lined up without displacement, or at exact right angles.

 

[NDT]

I would inspect each and every pulley for nicks. I would put a straightedge on each pulley to make sure it’s not out of plane.

 

[Thunderbirds]

In my case the most upper pulley attachments bolt was lose, but still held everything in place. It also pushed the belt forward a bit due to the incorrect angle. You can barely notice the alignment when looking, but when I removed the belt it rattled around. Didn't cause my belt to tear, but enough strain on one side i replaced it.

 

[SubstanceP302]

Thanks, I’ll certainly recheck all pulley bearings, bolts, and alignment when I take this belt off.

I was just wondering if anybody had any experience specifically with the belt sliding forward on the crankshaft pulley. I didn’t know if that can be indicative of something outside the pulley system like motor mounts.

also wondering if anybody has had success with alternate aftermarket 98 inch serpentine belts. This one felt very tight going on at 98 3/4. If that’s the case, would it make it more prone to slipping when the motor moves?

 

[Thunderbirds]

Thanks, I’ll certainly recheck all pulley bearings, bolts, and alignment when I take this belt off.

I was just wondering if anybody had any experience specifically with the belt sliding forward on the crankshaft pulley. I didn’t know if that can be indicative of something outside the pulley system like motor mounts.

also wondering if anybody has had success with alternate aftermarket 98 inch serpentine belts. This one felt very tight going on at 98 3/4. If that’s the case, would it make it more prone to slipping when the motor moves?

I used the Bando 8PK2490, which is 249 cm (2490 mm) equals to 98 inches... It works quite well for my 1999 M1123:

Amazon.com

 

[Gcelevator]

Check the alternator shaft, make sure the bearings are good, make sure the bottom bracket of the alternator is tight. Check the tensioner, make sure is not bouncing excessively and lastly make sure the rear section of the tensioner (the stop bump) is not cracked. That is taking in consideration all the pulleys are in good shape. Make sure the crank shaft damper/pulley rubber is in good condition.

 

[SubstanceP302]

Check the alternator shaft, make sure the bearings are good, make sure the bottom bracket of the alternator is tight. Check the tensioner, make sure is not bouncing excessively and lastly make sure the rear section of the tensioner (the stop bump) is not cracked. That is taking in consideration all the pulleys are in good shape. Make sure the crank shaft damper/pulley rubber is in good condition.

Will do… I didn’t even realize there was rubber in the crankshaft pulley… I will definitely check that.

 

[Retiredwarhorses]

Version of serpentine setup determines correct belt…for OEM, that would be 3 different length belts.

 

[SubstanceP302]

Yes…I have the non-A/C, lower serial number 6.5 with 98” belt.

 

[SubstanceP302]

Update: This might be helpful to anyone else who has the same issue

I took the most recently destroyed belt (Gates Micro-V K080981) off and inspected the pulleys and brackets more closely. All pulleys spin freely and are aligned, no broken bolts, crank pulley rubber isolator is in good condition.

However, the power steering pulley grooves are in really rough shape. Pictures attached.

That being said I put a new cheap belt back on so I could drive the vehicle while I wait for the new pulley. The belt is actually 98” while the last gates belt was closer to 98 3/4”. Now there is significantly less tensioner movement and the belt is not coming off the crank shaft pulley after a day of diving around town. So it’s possible the damaged power steering pulley is not actually the problem and the belt was just a little too big.

We will see…can’t believe the system in that sensitive to 3/4” belt circumference.

 

[Retiredwarhorses]

The proper belt is :

12469149-1 / 01-466-9476 / 3030-01-466-9476 - BELT, SERPENTINE (HMMWV) {196900 AND BELOW} [2481MM / 97.67 IN] | Hummer Parts Guy (HPG)

www.hummerpartsguy.com

the tensioners are also a problem if the correct tensioner isn’t used

 

[SubstanceP302]

OK…97.67” which means the gates belt was > 1” too big…maybe that was it.

 

[Coug]

Another possibility for an early serial number truck is the rear mount stud for the generator is sheared off and allowing the generator and PS to flex forward a little under load. I had this happen and could watch the belt move when the glow plugs were pulsing

Just something else to check.

Sheared generator bracket bolts.

When I first got the truck(m1123, 200 amp generator) the stud on the exhaust that holds the rear generator bracket was sheared, and a couple of the front bolts were loose. It started making noise again, so I checked, and the exhaust stud is sheared again, and at least one of the front bracket...

steelsoldiers.com

 

[SubstanceP302]

Thank you, I will recheck that as well. So far, the 98” belt vs the 98.75” belt seems to have solved the problem.

This was a cheap belt I did as a stopgap just so I could drive it around, i’ll probably swap it out with the 97.67” OEM belt soon.