Whine and how to isolate it

[LagunaH1]

When I drive my truck for, say, 2 hours or more it will start to emit a high pitched whine. It's hard to tell where the sound comes from, but I *think* it's coming from the front end, and the sound only seems to occur when I am lightly on the gas, or not fully off the gas. In other words, if I feather the throttle just right to make the truck neither coast nor pull, and then add a little bit more, then the sound occurs.

If I'm hard on the gas or completely off, then the sound doesn't happen.

Does anyone have any good suggestions for how to narrow down which component it might be that makes the noise? My first thought would be a mechanic's stethoscope but that's kinda difficult to use under the truck while driving......

Due to how the sound occurs I'd guess that it is driveline related, either a hub or a bearing.

 

[alrock]

Well, it's either engine speed related or vehicle speed related. If it's engine speed you should be able to recreate it when stationary, after the truck has warmed up (since you say it takes a while for it to appear). If vehicle speed related, you should hear it with the transmission in neutral and the truck rolling along.

If you feather the throttle like you described, but in neutral, can you replicate the sound?

A stethoscope can help if you can get it on a lift somehow, and use the throttle as you described.

 

[LagunaH1]

Good points.... I did try to rev the engine while in neutral and that didn't make any difference. I'm convinced the sound is speed and load related

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[Zach]

Uhhhh drive it like you stole it? Have been chasing noises for months in mine. Think I finally got it squared away. Put it up in the lift with Mike and am sure he'll find it.

 

[3Hummers]

Hub gears?

 

[Green 1]

I go back too what is the last thing that was worked on. T-case

 

[LagunaH1]

The noise was present before the new T-case was put in so I think that pretty much rules out the T-case. I'm thinking hub gears, carrier bearing or front diff.

Edit: I guess the challenge is that it takes quite a bit of driving before the noise occurs, and as I learned first hand in Moab this past October, sounds travel *a lot* in the drive train on these trucks.

 

[3Hummers]

Carrier bearing should be easy to check.

 

[4speedfunk]

Pinion bearing.


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[Reloader]

Yep, sounds like possible front diff issue. See if your mechanic has a set of chassis ears. These are sensors you can attach to various driveline componants and send sounds to a reciever inside cab whilst driving . You listen with head phones and switch between sensors to determine noise location. They work pretty good for this.
I know you had the front diff cover off in Moab and nothing looked bad but maybe you should have the shop pull cover again and closely check wear pattern on front ring and pinion.
The symptoms you describe would have me looking at that and bearings. Lots of extra moving parts in those H1 drive trains. You had one of the hub gear assemblies leaking lube in Moab if I remember right.

 

[LagunaH1]

That's a real good idea with the chassis ears, I didn't know such a gadget existed

Based on how the sound appears and how the truck feels when it happens, i'd say either front diff or a bearing in one of the hubs. I'll chat with Mike about this, thanks for the suggestion :-D

 

[Reloader]

Yeah the few times I've used them , they helped nail the problem and you would be surprised how far the sound can travel from the problem. Usually the shop has this tool or some tech working there does. They sell them on the tool trucks and the newer ones are wireless so you don't have to worry about wires getting tangled up in drive lines.