Strange sound coming from rear end

[OktobrVega]

Been driving my truck for about a week now. The truck sounds normal for first mile, after things warm up. It starts to sound like a dry bearings sound in rear end. Really pretty loud.

I give the vehicle gas and under load sound goes away. Then let of gas like in a coasting situation and it sounds like bearings are dry or like gear lash. Give gas again and sound goes away till like 45 then sounds pretty bad. Hubs are at spec with lube oil.

Asked Wehring and he said his trucks all do this too, asked others and their trucks do not make this sound.


Any ideas? And how difficult is the rear end tear down?

Thanks

 

[Suprman]

I believe they have planetary hubs so there is gearing there also. Did you check the fluid first? I have new in the crate complete rear ends for the 5ton lmtv I think they are the same for the 2.5t.

 

[73m819]

Check for a bad U-joint, I have driven about a dozen LMTVs, NONE had this noise.

 

[quickfarms]

Your problem is you are giving it gas

 

[tennmogger]

My 1994 LMTV does something similar. Same quiet operation as long as there is a little acceleration, then a rattle noise when speed is reached and coast is achieved. just a little more fuel applied and the noise goes away again. I am estimating worst speed is about 40 mph. At higher speeds the noise either disappears or the other sounds from the truck drown out that specific vibration.

What is different from yours is that my noise seems to come from the front. I think it is nothing more than a vibration of some loose part, or of a contact point somewhere.

It's easy to check all reservoirs for level. Next step I did was drain a little fluid and check the magnets for trouble. The front diff had a little fine magnetic stuff on it so it was drained and refilled with Amsoil Severe Gear. Drive shaft U-joints can also be verified tight.

If I might ask a related question, my LMTV has Meritor drive shafts and they look newish. Does yours? Does that mean they have been replaced? Axles are Rockwells, I think, so I assumed driveshafts would be Rockwell also. Maybe shafts are all Meritor.

Bob

 

[Suprman]

There should be a D stamped on the data plate its a bit larger than the serial lettering. That means the front driveshaft was updated the original design had issues.

 

[Lmtv772]

I thought it's the rear shaft that had issues (???)

 

[OktobrVega]

Almost exact experiences Tennmogger. I'll check for the D and see if I can identify. Trying to get NDT over and drive the truck so can pinpoint this down. Thanks again Will and all you guys willing to help.

Truck has always made this sound since I got it and fluids were all to spec

Sounds like metal roller skates on concrete hahah but it does. Also I feel it drag a little too when the sound is at its worst. Aside from that the truck is one the cleanest I've seen come out even though it's a 97. 11k miles

 

[tburk49760]

I'll be paying attention to this thread as my 614 mile when I got it Lmtv does this exact thing. I spent several hours under it tonight looking and wiggling while raising first one then the other front tire. Was happy to find grease zerks on the front axle u joints. Everything was greased and nothing was either too hot or loose. I'd prefer to find the issue before it destroys anything too spendy.

 

[OktobrVega]

UPDate** With help of a fellow member (NDT) found that the sound I was having was actually in trans/rear of engine area. NDT noticed something i didnt even catch and that other LMTV owners should make sure of. My drive shaft was almost 45 degrees out of phase. I droped the drive shaft and realigned it. Although significantly reduced my sound is still present, but now only happens after 40mph. Still usually on coasting. Im thinking possible pinion bearings are shot. Yoke didnt have excessive play, or unusual sounds.

Next step is get it up on jacks and run it and see if I can pin point the dry bearings sound. This is difficult as the sound isnt constant, and only happens during certain speeds, and during coasting. Cant tell if the phase caused the issue or during troubleshooting, maintanence just threw the truck together for deactivation.

Any ideas?

 

[Blackmagic94]

So is yours stamped D or not?

 

[OktobrVega]

No D stamp, but mines a 1997 surely this one got the new shaft right. Thought I read 100% of the units were corrected. By time the A1s went into production.

 

[mkcoen]

Were you ever able to resolve this?

 

[tburk49760]

I changed some ujoints and mine went away.

 

[Suprman]

One of the army mechs told me there was a warning on the u-joints. Any more than .025 end play and they can blow apart. I dont know how to measure it though.

 

[MaiNiaK]

I thought it's the rear shaft that had issues (???)

Ive only heard of the issue they had with the front drive shafts. They would come off the front hit the ground and send soldiers through the windshield.

 

[radbad]

Any update on this? Planning to dig into my truck soon - there's a pulsing rubbing noise around 40mph when off the gas.

Thanks!

 

[Suprman]

In the TM is a "driveshaft hinging test" it shows how to check for excessive play. Excessive play anywhere in the driveline will lead to all kinds of issues to include throwing driveshafts.

 

[o1951]

Ive only heard of the issue they had with the front drive shafts. They would come off the front hit the ground and send soldiers through the windshield.

When I helped prepare weekend racer cars, we were required to install driveshaft safety straps to prevent that. Basically, they were a steel loop that would catch broken shaft before it hit the ground or went wild and tore thru the floor. Shaft would just buzz around in the loop as car came to a halt.

 

[radbad]

We dug into this on our truck tonight a bit. Greased the zerks for the splines on each drive shaft and also the u-joints on either end of both shafts.

I don't have a mounted dial indicator to perform the Driveshaft Hinging Test, but I used my sense of touch and felt no play whatsoever. Granted, .020" play isn't much, but I would think I could feel something if there was play.

Also happened to have my legs resting on the floor of the cab during a test drive this evening and noticed that I can feel the vibration on the cab floor. Seems like it would have to be pretty significant to be felt like that.

We're going to take the truck out this week with a go pro fixed to a few spots underneath to see if the mic can help locate the source of the sound.