Grinding while coasting in 4hi

Hi all. Need some advice.

When I first bought my 07 DC 4x4 in January I noticed there was a very very slight grinding or whirring from the front end in 4hi but just assumed it was normal (this is my first true 4x4 vehicle). I put the truck into 4hi this last week to lubricate the diffs per the user manual and now the noise seems louder (or I have just gotten more sensitive to it.). It is very very minimal when applying throttle, but becomes much more noticeable when coasting. Goes away completely in 2wd.

Three questions:
1) how much noise is normal in 4hi? I’ve read posts that say some noise is normal and others that say no noise.

2) is it more likely that the noise is coming from front diff or t case? I’d like to try to put fresh fluid in and see if it mitigates the issue as I don’t have cash to replace either component. Would like to know whether to start with front diff or t-case with the fluid changes.

3) How likely is it for the front diff or t case to actually break? Am I ok letting this ride if the fluid changes don’t solve it? As long as nothing is going to get ruined I can live with the noise. I am even ok just not using 4wd if necessary. Mostly just want this truck to last at least 3 or 4 more years to tow and daily driver uses.

I should also say that when I bought the truck with 170k, all diffs fluids had only been changed once at around 90k. My mechanic said rear fluid looked worn but not worse than it typically would after a normal fluid change interval, and front diff fluid looked like new. He only changed the rear fluid. I can’t remember what he said about t-case but I’m pretty sure it looked new too.

Any info or advice would be appreciated. Please put my mind to ease!

 

Diagnoses would be to check all of those things. Starting from most obvious or easiest.. I'd try putting new fluid in front diff and transfer case. Also lubricate the front drive shaft I believe it has a grease zerk. On my 07 it has a clunk when shifting out of 4wd back into 2wd only sometimes. Which I believe to be normal for these trucks. Also when I put mine in 4Low for the first time it made a high pitch whining noise so I took it out and back in a few times to lubricate and to make sure it didn't get too hot. After a few times it stopped making the high pitch whining noise.

On my 92 4runner rock crawler I can recall a similar problem when coasting in 2wd it was whining and not sounding right at all.. what happened was the rear diff was actually seizing. All the differential fluid leaked out when I didn't tighten the bolts, I must have forgot. It complete grenaded and it was like heavy braking while i was driving down the road. Hopefully nothing is seizing on yours I highly doubt it. But just another experience of mine.

 

Update: Problem Solved.

Finally got bad enough that shop could easily hear/feel it - started doing it in 2wd and at different speeds too. They drove it on the rack and listened with a chassis ear and realized it was actually rear wheel bearing. Apparently those are really a PITA to change out because all said and done it cost me $900. The shop had to spend extra time "impact calibrating" the backing plate because it was rubbing on the brake after reinstallation. Truck drives like a dream now.

All said and done, I bought the truck in Dec 2017 with 168k and since then it's gotten:

- 2x drain and fill on transmission, all diffs, t case
- New coil springs, struts, and shocks (TRD off-road OEM Bilstein stuff)
- New windshield
- Rear wheel bearing replacement - was scratched by rocks in windshield wiper by previous owner
- Alignment and tire balance
- Replace gas tank straps (rusted through)
- Replace all brake lines (were very rusty)
- Replace rear exhaust hanger (rusted through at exhaust)

Here's what's on the docket for the next year:

- Corrosion warranty extension - New frame for free??? fingers crossed...
- New tires - Michelin LTX M/S whatever they're called now
- New Brake rotors and pads all around - Powerstops
- LED lighting all around, exterior and interior
- Replacing sub with something with a flatter response
- Replacing audio amp - mine is acting up intermittently. Need to decide if I want to go aftermarket or stick with the stock unit. I kind of want an in-line pro sound grade graphic eq to tame the sibilance of those JBL tweeters.

Eventually will need:

- New bed. Getting pretty damn rusty.

Gonna try to make this machine last for half a million miles...