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

[Tracer]

From what my old ears can hear in the video, it sounds like something is loose and rattling. As wrenchturner stated, start checking for loose items. I have had rattles in my deuce that have driven me up a wall, one was a copper airline rattling against the fire wall. No noise at idle, but once underway the rattle would start.

 

[Swamp Donkey]

I'd take Wes up on his offer. Seriously. It's a shame this has been going on so long without a diagnosis, much less a repair. All these paid mechanics that have looked at the truck are missing something in their troubleshooting methods. I had high hopes that the college would figure it out. But I digress...

My offer still stands...get it to me and I'll sort it out for you. Easier said than done I know...but having Wes come up there will get you the same results. He'll find the problem. Keep your head up. I'll holler at ya this evening.

 

[Oldworldtenacity]

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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Wow, thats a really nice offer...and yeah I know swamp was up for it too..problem is that shipping it down there was to high. I'll probably be contacting you after Thanksgving. Fleetpride wants me to come down there next week to ride with them on it and i may let them try one more day on it before I take you up on your offer.

Also, all ROPS mounting and cab mounts has been checked and we have ruled out anything being loose pertaining to the body/bed. If you listen to the videos closely you can hear that the grinding/clanking is in conjunction with the rotation of the drive shafts...or so it sounds that way. Crazy because we eliminated it being the shafts, Ujoints, bearings...and I cant even remember everything at this point to be honest. I'll keep you posted and thanks.

 

[Oldworldtenacity]

Yep, everything tight. See my respons to Simp5782.

 

[Oldworldtenacity]

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

Yep, everything tight. See me response to Simp5782.

 

[Oldworldtenacity]

I'd take Wes up on his offer. Seriously. It's a shame this has been going on so long without a diagnosis, much less a repair. All these paid mechanics that have looked at the truck are missing something in their troubleshooting methods. I had high hopes that the college would figure it out. But I digress...

My offer still stands...get it to me and I'll sort it out for you. Easier said than done I know...but having Wes come up there will get you the same results. He'll find the problem. Keep your head up. I'll holler at ya this evening.

I know man, I cant believe it myself especially after talking with the guys at Fleetpride yesterday. They don't know anymore than the students at the Technical school.

 

[wrenchturner6238]

When your transmission was out did you check the flywheel housing bolts to make sure they were in and tight? It sounds like it would be worth you time and money to take simp5782 up on his offer

 

[Oldworldtenacity]

When your transmission was out did you check the flywheel housing bolts to make sure they were in and tight? It sounds like it would be worth you time and money to take simp5782 up on his offer

Well, the technical schools checked it and said there were no loose bolts. The teacher there thinks that it is the flywheel causing my problem after pulling all of the shafts and other troubleshooting with the T case. Others disagree with that and Fleetpride is just flat out clueless at this point lol.

 

[simp5782]

Just let me know when. I would probably only need a day. Two at the most to figure it out. Not including a repair. Something heavy i cant do being that i will only have my on board tools.

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[sandcobra164]

My Deuce used to creak and grumble when driven the same way. I'll bet it's spring pack or dog bone related. Possibly the bed mounts but I'd bet it's nothing worth selling the truck over. I never solved the issue on my deuce, the biggest "crack" sound would occur when turning right onto my dirt road at around 30 mph. I know it's an apples to orange comparison and my 5 ton doesn't have any of the noise that I've heard. Mine does have that loud 250 Cummins, it may be making noises I don't hear? The engine noise on the 5 ton gets somewhat quiet when making the turn. The deuce had a C turbo and it would be whistling at idle during the same turn but I'd hear the clunk. I'd put my foot into it anyway. I hope you find the solution and share with us. Now crawling around at idle in the 5 ton and flexing the suspension, mine makes similar noises in the school bus turn around. It has some deep but dry ruts.

 

[146APF]

Could be the rear transmission mount bracket is contacting the cab,my truck sounded same ....see post #9 Russ Knight Drive train Noise post.

 

[lindsey97]

Does it make the noise sitting still, in neutral, revving the engine up?

Have you checked for "extra" bolts/nuts/washers laying in the bottom of the bellhousing, being thrown around by the torque converter?

Does the transfer case have oil in it? Is the oil pump working on the back of the transfer case?

Have you checked your knuckles and front wheel bearings?

Have you checked the parking brake assembly on the back of the transfer case? Are there loose, broken parts tumbling around in the parking brake drum as you drive around?

 

[lindsey97]

Could be the rear transmission mount bracket is contacting the cab,my truck sounded same ....see post #9 Russ Knight Drive train Noise post.

(2) 15/16" bolts hold the rear transmission mount in place, and there is a rubber resilient mount there.

Crawl under the truck with a flashlight, look for any wear spots in paint that are fresh and rusted, anywhere components of the drivetrain are bolted into the truck.

Could it be the spare carrier?

 

[Oldworldtenacity]

Does it make the noise sitting still, in neutral, revving the engine up?

Have you checked for "extra" bolts/nuts/washers laying in the bottom of the bellhousing, being thrown around by the torque converter?

Does the transfer case have oil in it? Is the oil pump working on the back of the transfer case?

Have you checked your knuckles and front wheel bearings?

Have you checked the parking brake assembly on the back of the transfer case? Are there loose, broken parts tumbling around in the parking brake drum as you drive around?

All of those things have been eliminated and the problem has to do with the RPM of the speed of the shafts turning. It gets worse the more torque is placed on the truck under acceleration..especially on grades. I'm definitley gonna have Fleetpride check the rear Transmission mounts next week though.

 

[Oldworldtenacity]

Could be the rear transmission mount bracket is contacting the cab,my truck sounded same ....see post #9 Russ Knight Drive train Noise post.

Was yours temp sensitive like mine is? When its hot out it does it right away, but if I take it out in colder weather like now I have to romp on it for at least 5 minutes before it starts to get bad...so it has to be warmed up to be fully revealed. I'm defnitley gonna have the those mounts checked though.

 

[146APF]

Yes,it was heat sensitive.The transmission tailshaft moved upward 1/2 inch after loosening mount bolts.It's binding/preloading the upper bushing.Loosen the bolts and insert a piece of rubber between cab floor and mount(I used a leather glove,all that was available at the time) for temp repair to verify issue.The contact was transfering all the driveline noise,squeaking etc sounded exactly like yours.

 

[Jbulach]

This is fun, I’m going to guess exhaust system? Hard to tell from a video and whats really been done/eliminated and by who?

At this point if I where you, I’d take Simp up on his offer, maybe if your not in a hurry he’ll be headed in your direction anyhow, save you some money and make him some more fuel money?

 

[Tracer]

This is fun, I’m going to guess exhaust system? Hard to tell from a video and whats really been done/eliminated and by who?

At this point if I where you, I’d take Simp up on his offer, maybe if your not in a hurry he’ll be headed in your direction anyhow, save you some money and make him some more fuel money?

I agree. You've tried just about everything else.

 

[silverstate55]

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.

My 931A2 (RRAD rebuild 2005) had this exact same problem; removed the front driveshaft & found that the front output shaft was broken off inside T-case, and pieces were lying on bottom inside case (per 98G I put some strong magnets on bottom of case to hold them in place while driving). Noises similar to OP's were from remaining ball bearings rattling around inside bearing carrier....about half of the ball bearings were rolling around inside the bottom of the T-case, I fished around for about 30 minutes with a magnetic parts finder to try to remove all the shavings/pieces I could.

Simp5782 hooked me up with a good take-out T-case to replace it with.

While searching around for replacement parts, it seems that these things are virtually impossible to find parts for. Oshkosh Equipment listed some of them, but then told me that they were subject to minimum-quantity requirements and would be pretty expensive to tool up a run for.

 

[Oldworldtenacity]

Yes,it was heat sensitive.The transmission tailshaft moved upward 1/2 inch after loosening mount bolts.It's binding/preloading the upper bushing.Loosen the bolts and insert a piece of rubber between cab floor and mount(I used a leather glove,all that was available at the time) for temp repair to verify issue.The contact was transfering all the driveline noise,squeaking etc sounded exactly like yours.

Wow, very interesting to hear this could be the problem with mine...especially if it was making the same noise and temp sensitive. Youve got my hope up now lol...hoping it wont be crushed again next week ha! This will be the first thing I have them look at next Monday