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I dont know if this is more of a transfer case issue or a differential issue, I was hoping you guys/girls might help me shed some light in the subject. Here is the scoop.....
Let me start off by saying that none this happens while in 2x4. FWIW, the truck engages into 4x4 mode rather easy. No clunking/thud is made when I shift from 2x4 to 4x4 (parked or while moving). I notice the thud/clunking sound predominantly after acceleration, either accelerating from a dead stop or accelerating while cruising, it doesnt matter. I can feel it in the front end. The clunking/thud is deff coming from the front end. It may be doing it in the rear, if it is I cant hear it. It is quite loud at times. I wouldnt call it a violent thud, maybe an agressive thud.
Additionally, I noticed another noise/issue while backing up in 4x4 a day or so ago.....while backing up it there was a sound coming from the front/under that sounded grinding/whinny noise. The noise kinda resembles the sound of "grinding the gears on a manual transmission/clutch". Although this sound was more whinny than grindy. Nonetheless, the sound my truck made when this happened was still similar to the gear grinding sound that happens on a stick shift automobile. Additionally, the intensity of the sound was greater with more acceleration. Again, this noise only happened while in 4x4 and while moving in reverse.
I bought the truck about a month ago. It has about ~70k on the odo right now. I am going to differentials, transfer case, and a tranny service soon. I dont know if the noise(s) are due to a lack of service. However I was wondering if you think a fresh differential/transfer case service would take care of things. What do you think, is this a differential issue or a transfer case issue?
The grinding noise=sounds kind of like ice in a blender or sheet metal being dragged? That is from the IWEs not being fully engaged with the hubs on the front wheels.
The clunk, if occuring at the end of a "grinding noise" is the IWEs re-engaging with the hubs.
Possible causes are leaks within the vacuum system (to include the IWEs themselves) that operates the 4x4 on our trucks, or an intermittant malfunction of the solenoid that turns on/off the vacuum to the IWEs.
The good news is troubleshooting and repairing is relatively easy. These two threads are my "go to" sources for info on the issue.