HMMWV Serpentine Belt Issue - 6.5L

Derrinh

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I’m having an issue with my serpentine belt shredding on my M1123 (pictures attached). It looks like it’s slipping off center and maybe getting caught up on a bolt. Anyone else had any issues with this? Is it typically a belt tensioner issue?

I appreciate any help!
 

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avman

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Yes, had the same problem with my 1123. Replaced 3 belts until I put on a Napa micro v 25 081102. Been on for 11000 miles with no problem.
 

Derrinh

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Yes, had the same problem with my 1123. Replaced 3 belts until I put on a Napa micro v 25 081102. Been on for 11000 miles with no problem.
Thanks for the advice and part #. I’ll give that a try. Does your truck have the red dot ac? Just want to make sure I get the right length belt as I do have the red dot ac.
 

Coug

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I tried finding the belt listed above on the NAPA website but it isn't showing up for me.
Gates K081102 is the same belt (and judging by the NAPA part number NAPA is buying them from Gates)

For tensioning, I can barely force it on by hand with no tools, but using a ratchet or breaker bar on the tensioner makes it a lot easier.
If yours is easy to install then there is definitely something wrong with your tensioner, or maybe one of your other pulleys is the wrong size or something? I mean, it shouldn't jump out of the grooves unless something is pretty far out of whack.

Do all the pulleys spin freely? It doesn't look like there is any damage to the belt back like it's slipping.

Also just to check, is the belt you have on 6 ribs or 8? The civilian trucks used a 6 rib serpentine belt, the military used 8

The one listed above is 8 ribs. And yes, I can confirm it's the correct part number for use with the Red Dot compressor. (my thread below)

 

Derrinh

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I tried finding the belt listed above on the NAPA website but it isn't showing up for me.
Gates K081102 is the same belt (and judging by the NAPA part number NAPA is buying them from Gates)

For tensioning, I can barely force it on by hand with no tools, but using a ratchet or breaker bar on the tensioner makes it a lot easier.
If yours is easy to install then there is definitely something wrong with your tensioner, or maybe one of your other pulleys is the wrong size or something? I mean, it shouldn't jump out of the grooves unless something is pretty far out of whack.

Do all the pulleys spin freely? It doesn't look like there is any damage to the belt back like it's slipping.

Also just to check, is the belt you have on 6 ribs or 8? The civilian trucks used a 6 rib serpentine belt, the military used 8

The one listed above is 8 ribs. And yes, I can confirm it's the correct part number for use with the Red Dot compressor. (my thread below)

Hey Coug,

Thanks so much for all the info. That other post you linked was super helpful as well.

So as far as tension, it’s just as you described. A little too tight to get off by hand but using the ratchet I was able to get it off fine. Pulledthe belt off and it measures about 126”. And found the part number printed. Looks like it’s a belt specific to red dot.

All the pulleys seemed to be spinning freely and none seemed bent or wobbly. I put the belt back on centered and will see if it slides over again. Ordered a couple belts just in case.

I took video of the belt with the motor running and you it’s definitely pulling to the one side (closer to the cab). It also seems to have a rev-up every so often...not sure if that has to do with the belt issue and something holding it up...maybe a bearing. Not quite sure. But thank you again for all the help and we’ll see how it goes with this belt and once I get a new one on.
 

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Derrinh

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Las Vegas
I tried finding the belt listed above on the NAPA website but it isn't showing up for me.
Gates K081102 is the same belt (and judging by the NAPA part number NAPA is buying them from Gates)

For tensioning, I can barely force it on by hand with no tools, but using a ratchet or breaker bar on the tensioner makes it a lot easier.
If yours is easy to install then there is definitely something wrong with your tensioner, or maybe one of your other pulleys is the wrong size or something? I mean, it shouldn't jump out of the grooves unless something is pretty far out of whack.

Do all the pulleys spin freely? It doesn't look like there is any damage to the belt back like it's slipping.

Also just to check, is the belt you have on 6 ribs or 8? The civilian trucks used a 6 rib serpentine belt, the military used 8

The one listed above is 8 ribs. And yes, I can confirm it's the correct part number for use with the Red Dot compressor. (my thread below)

Oh and it’s definitely an 8 rib belt...but about two of the bands have been ripped off :/
 

Coug

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Hey Coug,

Thanks so much for all the info. That other post you linked was super helpful as well.

So as far as tension, it’s just as you described. A little too tight to get off by hand but using the ratchet I was able to get it off fine. Pulledthe belt off and it measures about 126”. And found the part number printed. Looks like it’s a belt specific to red dot.

All the pulleys seemed to be spinning freely and none seemed bent or wobbly. I put the belt back on centered and will see if it slides over again. Ordered a couple belts just in case.

I took video of the belt with the motor running and you it’s definitely pulling to the one side (closer to the cab). It also seems to have a rev-up every so often...not sure if that has to do with the belt issue and something holding it up...maybe a bearing. Not quite sure. But thank you again for all the help and we’ll see how it goes with this belt and once I get a new one on.
So looking up part numbers and crossing it to an NSN ( 3030-01-524-2460 ), the belt in your hand is for a truck with a serial number higher than 196901, and the one I posted is a shorter belt, for trucks with a serial number 196900 and below. For my truck it's only 110.75 inches, so if yours measures out to about 126 then it's definitely not going to be the same belt.

hmmwv serp belts1.jpg


Last two NSNs on this page are the red dot belts for our trucks (or at least that's where they are when I bring up the page)
 
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Derrinh

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So looking up part numbers and crossing it to an NSN ( 3030-01-524-2460 ), the belt in your hand is for a truck with a serial number higher than 196901, and the one I posted is a shorter belt, for trucks with a serial number 196900 and below. For my truck it's only 110.75 inches, so if yours measures out to about 126 then it's definitely not going to be the same belt.

View attachment 823495


Last two NSNs on this page are the red dot belts for our trucks (or at least that's where they are when I bring up the page)
Oh got ya. Thanks for finding that. Yeah I ended up finding the correct belt for mine (the last NSN in that awesome graphic). Thanks again! We’ll see what happens.
 

Derrinh

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Are all the pulleys lined up front and back? Maybe one is too far forward? Just a thought.
Yeah I started wondering that as it seemed like the tensioner pulley was actually out a bit more than the rest...the belt seemed most off on that one. I’ve read up a bit on checking alignment and had a laser level lying around so I tried that but couldn’t quite get the angles right to tell.

Any idea if there is adjustment in and out for that tensioner? When I had the belt off and was checking them, it didn’t seem like it had any play.
 

Action

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There are drawings with measurements, in a HMMWV TM, for how to construct a pulley alignment tool. Just a couple pieces of flat metal attached together. It works well. Search the pdfs for "manufactured items" to find it faster.
 

Derrinh

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Las Vegas
There are drawings with measurements, in a HMMWV TM, for how to construct a pulley alignment tool. Just a couple pieces of flat metal attached together. It works well. Search the pdfs for "manufactured items" to find it faster.
Great, thanks for the heads up! I’ll get on that.
 

Sigi

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I had a similar belt shredding problem on a Detroit Series 60. Turned out to be a tensioner bearing that locked up intermittently. It still spun when I tested it by hand but you could feel some wear. Mine locked up off and on when the bearing got hot. Wasted a lot belts.

I'd take the belt off and spin all pulleys including the tensioner. If you hear any bearing grumble it is time to replace that bearing.
 

Mullaney

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I had a similar belt shredding problem on a Detroit Series 60. Turned out to be a tensioner bearing that locked up intermittently. It still spun when I tested it by hand but you could feel some wear. Mine locked up off and on when the bearing got hot. Wasted a lot belts.

I'd take the belt off and spin all pulleys including the tensioner. If you hear any bearing grumble it is time to replace that bearing.
.
Nice idea - and even better with experience behind it! Thank You.

AND, it looks like you might be a new guy around here just based on the numbers.
Welcome to the outfit and thanks for contributing to the knowledge here!
 

phemer

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I've having the identical issue w/ the 6.5 1123 w/ reddot AC. Did the new belt (micro V 25 NAPA) fix the rib-jumping issue? Always placed correctly then upon start, immediately jumps a rib.
 

Action

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I've having the identical issue w/ the 6.5 1123 w/ reddot AC. Did the new belt (micro V 25 NAPA) fix the rib-jumping issue? Always placed correctly then upon start, immediately jumps a rib.
I had a belt be 1 rib off on a pulley before. It was just installed wrong. After a bit of driving, that 1 rib started to separate from the rest of the belt. As it spun around, the one rib section cut through a coolant hose. Coolant came out and steam covered windshields.
Make sure you belt stays in place.
 

phemer

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I certainly don't intend on driving it this way, however, I'll reset and correct the belt placement then upon starting motor - climbs over that rib every single time. Belt seems stable once it climbs over that one rib - but still not correct. Still troubleshooting. If anyone else has any suggestions / solutions, I'm all ears.
 

Action

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I certainly don't intend on driving it this way, however, I'll reset and correct the belt placement then upon starting motor - climbs over that rib every single time. Belt seems stable once it climbs over that one rib - but still not correct. Still troubleshooting. If anyone else has any suggestions / solutions, I'm all ears.
Which of your pulleys is the belt riding up on? Has it done this since you got the hmmwv? or just started? Have you looked into the pulley alignment tool mentioned in post #12 ?
 

phemer

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Scottsdale, AZ
Which of your pulleys is the belt riding up on? Has it done this since you got the hmmwv? or just started? Have you looked into the pulley alignment tool mentioned in post #12 ?
Hey ACTION,

The Sandin is the trouble pulley. I have never before seen this. I'll either reset the pulley to the correct rib or it will already be correct, but upon start, I'll notice the belt climb just one rib toward the cab (rearward) and ride up there. I'll kill the motor and it will snap back down to the correct alignment. I'll notice that when I engage the AC Compressor, the belt will (audibly) snap back down to the correct rib for a couple seconds, then snap back up to the incorrect position for a couple seconds then back again. It will do this non-stop when the compressor is engaged. Very strange.

The pullies are lined up perfectly as I can tell visually. I've also built multiple race motors, race bikes, etc (very mechanically capable).

I have the original belt, a Dayco Gold, that I swapped for another manufacturer version a few months ago out for some preemptive maintenance. I can try an swap that back.

I suppose there's a possibility that I just just never noticed the rib-jumping issue? So far it shockingly doesn't seem to damage the belt.

My diagnostics included: had it running at idle for probably an hr in the driveway. No issues. THEN I locked the throttle half open for prob 5-8 minutes, came back out and it seems to have purged 1/3 my steering fluid (ATF) reservoir all over my driveway via the overfill/vent line. That's another can of worms I will have to get into at a later date.

What a pain.
 
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