M923a2 clanking grinding noise from under cab? Transfer case or U joint?

[Oldworldtenacity]

I finally got a chance to take some videos with my new phone that have good audio so I posted them on Youtube.

The truck has been making this clanking grinding noise that does not really start until after driving the truck around for a good 10 minutes which tells me it probably has to do with the Transfer case.

I replaced the Transmission back in February due to a transmission issue and hoped it would resolve this problem as well, but that wasn't the case unfortunately.

The noise is worst when you punch the throttle from a dead stop or stop on a hill. It will also do it sometimes when not accelerating and going over large bumps as well.

Most I have talked to or rode in the truck with me are saying it is either a U joint or something like a bearing in the transfer case because of it not starting until the truck warms up.

Here are 3 videos of how it acts.

https://www.youtube.com/watch?v=yZEP5p6duek


https://www.youtube.com/watch?v=WwWaJhUOA4U


https://www.youtube.com/watch?v=kjj7Ly0l5zE

 

[acme66]

I think a u-joint bad enough to make that noise would be clearly obvious with a shake of the joint by hand. Get in there and pry on them with a bar just a little bit. I think I would drain the t case and look for glitter. You haven't got something that rubs on the motor/tranny/t case when the engine mounts flex under acceleration do you? Something that might resonate up through the floor? What about the rear ends, and carrier bearing in the back?

Ken

 

[Suprman]

The bed sides and racks shift and clunk around when driving. The bed itself can shift a bit also. The m939 frame has alot more flex than one would think from just looking at it.

 

[Oldworldtenacity]

I think a u-joint bad enough to make that noise would be clearly obvious with a shake of the joint by hand. Get in there and pry on them with a bar just a little bit. I think I would drain the t case and look for glitter. You haven't got something that rubs on the motor/tranny/t case when the engine mounts flex under acceleration do you? Something that might resonate up through the floor? What about the rear ends, and carrier bearing in the back?

Ken

We checked the U joints and they are tight with applied force by Human hands...no play....they seem to be in really good shape.

Also can not find any evidence of any rubbing happening on the T case or tranny. Rear ends are great and no carrier bearings on these trucks...not like the A1.

The sound is coming from directly underneath the rear of the cab where the main shaft connects the the T case.

It did it slightly even when I picked the truck up at Ft Stewart in Feb of last year and got worse as time went on. N

It starts doing it like clockwork after driving around for 10-15 mins...so something tells me it is a heat based problem.

 

[Oldworldtenacity]

Considering that this truck had this noise coming and going from the time I picked it up after the supposed fresh rebuild 4 years earlier that all Frankencabs models and others definitely had, I am surprised no one else has chimed in about hearing this sound in another truck.

Really? no one has ever heard one of these trucks do this?...or another SEMI truck for that matter?

 

[Cobra03]

pull the front driveshaft off, and then drive it. I just had the same thing happen to mine. It takes ten minutes to get the driveshaft off. My front drive flange in the Tcase has play and the bearing is bad. I will be dropping the case and replacing the case and rebuilding mine for a spare later. It drives really good without the front shaft now.

 

[acme66]

Considering that this truck had this noise coming and going from the time I picked it up after the supposed fresh rebuild 4 years earlier that all Frankencabs models and others definitely had, I am surprised no one else has chimed in about hearing this sound in another truck.

Really? no one has ever heard one of these trucks do this?...or another SEMI truck for that matter?

Well that is a rough noise. Other than a flex plate coming loose from the converter on a SB350 I had in high school it is sort of new that you can have that sound and haven't let all the glitter out. Say come to think of it that might be something to check. It only made the noise under acceleration at first the slowly became more after time.

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[Plane Fast]

You could take a flashlight and look in the bell housing drain hole. See if maybe it's making metal.

 

[wrenchturner6238]

Mine had a noise that would come and go going down the road when I picked it up. The thing I found was that the t-case mount bolts were loose and it would kind of get out of align and the shafts u-joints would make a racket. I am not saying that it was the same noise but it couldn't hurt to make sure those bolts are tight. Does the t-case shift good in and out of low? I would try driving in low range to see if it makes the same noise then as well.

 

[Oldworldtenacity]

pull the front driveshaft off, and then drive it. I just had the same thing happen to mine. It takes ten minutes to get the driveshaft off. My front drive flange in the Tcase has play and the bearing is bad. I will be dropping the case and replacing the case and rebuilding mine for a spare later. It drives really good without the front shaft now.

hmmmm, I will probably try that. Are you saying that your front drive shaft would make a worse noise when under acceleration just like mine?

 

[Oldworldtenacity]

Well that is a rough noise. Other than a flex plate coming loose from the converter on a SB350 I had in high school it is sort of new that you can have that sound and haven't let all the glitter out. Say come to think of it that might be something to check. It only made the noise under acceleration at first the slowly became more after time.

Sent from my SCH-I535 using Tapatalk

Well, we replaced the transmission and it really didn't make a difference with that particular noise. I know it's hard to tell by listening to the video, but we have figured out that the noise is definitely coming from the drive line between the transfer case and shafts....not as far forward as the transmission.

 

[Oldworldtenacity]

You could take a flashlight and look in the bell housing drain hole. See if maybe it's making metal.

lol yep already replaced transmission with a new one in February. I was hoping that would make a difference to know avail.

 

[Oldworldtenacity]

Mine had a noise that would come and go going down the road when I picked it up. The thing I found was that the t-case mount bolts were loose and it would kind of get out of align and the shafts u-joints would make a racket. I am not saying that it was the same noise but it couldn't hurt to make sure those bolts are tight. Does the t-case shift good in and out of low? I would try driving in low range to see if it makes the same noise then as well.

Thanks for the advice. It does go in and out of low just fine and driving in low range did not make a difference with regards to the noise. Did your U joints show visual wear from the racket?....A drive line shop here told me last week that the shafts and joints were in great shape...so I left scratching my head of course.

 

[wrenchturner6238]

My u-joints are fine just tightened up transfer case mounts up noise went away. My noise was just because the drive shafts were getting out of align a little but would go back as you drive making it a come and go noise. I would take an oil sample from the transfer case and see if there is metal flakes in the oil and if it smells burnt.

 

[Oldworldtenacity]

My u-joints are fine just tightened up transfer case mounts up noise went away. My noise was just because the drive shafts were getting out of align a little but would go back as you drive making it a come and go noise. I would take an oil sample from the transfer case and see if there is metal flakes in the oil and if it smells burnt.

Yep, I've decided that taking an oil sample and disconnecting the front drive shaft should yield some indication as to what my problem is exactly. I'll update once I figure out what the culprit is.

 

[Shoprat 19th Engr]

I had A problem of the same sort and found that the flange bolts were loose on the shaft between the trans. and the transfer case thighten the bolts and no more noise

 

[Tracer]

Definitely check your transfer case oil. If you have a magnetic drain plug it will be covered with metallic particles.

 

[Oldworldtenacity]

Update: So after all this time we pulled a ll of the shafts out and the truck still does it. Does not matter if the front shaft is out or either of the rear shafts. So can't be axles and cant be Ujoints. Checked T case too and cant find anything. To make matters worse my truck has been at Fleetpride for the past 10 days and they are telling me they are puzzled by it as well. Neither of there best mechanics(supposedly) are certain either. I'm pulling my hair out over this POS at this point. The truck has basically set since last Summer and I got motivated to try and get the problem resolved so I can sell. what sucks is that this truck would be basically perfect if not for this magical issue that refuses to reveal itself.

Again here are the videos if anyone new here hasnt seen this thread since I last posted about it.

https://youtu.be/yZEP5p6duek


https://youtu.be/WwWaJhUOA4U



https://youtu.be/kjj7Ly0l5zE

 

[simp5782]

You can cover the shipping for me to bring it to memphis and ill fix it for free. I will come up and get it with my trailer and bring it back to you or you could fly down and drive it back. I like a challenge. I think swamp donkey may be up for it too.

My costs are just fuel and a little of my time. Not trying to make a profit.

Or i come up for a few days, you cover my fuel costs and hotel room and i will tell you exactly what it is.


Ill be somewhat helpful as far as diagnosis goes. Good way to check for suspension and driveline noises if you have another military truck available is to hook it to a towbar and ride around with truck off. Transmission and transfer case in neutral. Someone rides in the towed truck and listens. Alot quieter this way. Plus it gets the engine and transmission and jackshaft out of the equation as being a problem if its still happening. If the noise is still there drop components off in the driveline to find it.

Have you had all the ROPS mounting checked? There trucks radiate noise bad.
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[wrenchturner6238]

I have listened to the videos again with out driving myself and or being there. Have you checked and made sure there is nothing lose and hitting the cab or enough clearance that not hitting cab under torque, checked your motor mount for tightness or slack