Whining Front Diff - Next Steps?

Ever since my 100k service, I have been getting what I think is the drivetrain whine that so many have experienced. It happens when I'm on the gas between 53-59mph and gets louder the more throttle you give. The pitch doesn't fluctuate with RPM so I'm 95% sure it has to do with driveline. BTW - there is no adverse affect on performance other than the noise.

I took out my entire front driveline (diff, axles, front driveshaft) and have been driving around the last few days. The driveline noise is gone.

So now I am staring at my M205 on the floor of my garage, wondering what I should do next. Is it worth opening up and looking into? Can this noise be caused by not having enough fluid? Even if I open it up and find a problem, can I even do anything about it short of rebuilding the whole diff? Seems to be to just let it go until it really becomes a problem. I've heard people have driven 80k miles with whine...

What do you guys think?

 

When you say "gets louder the more throttle you give" do you mean the faster you go? If it was the front diff, it wouldn't matter how much throttle you're giving it in 2wd, it would be purely related to speed.

I would open the diff up myself and look for obvious signs of issues. Bad wear pattern, loose bearings, lots of metal particles, ect.

 

The only logical option is SAS

 

More throttle == louder noise
More speed == higher pitch

When I say "more throttle" I mean like if I'm going uphill and the car is working harder to maintain speed; I don't necessarily have to be accelerating.

It's REALLY weird to me because I am running in 2wd... so I'm confused how the front would be affected. I might have to do some more driving on some mountain passes. But in the 100 or so miles I've put on for now, I was having a hard time recreating the noise

 

Because everything in the front end is turning, from the wheels all the way back to the transfer case.

 

You could try putting the diff and axles back in. Leave the driveshaft out. See if the noise changes/comes back.

It kinda sounds like bad ujoints to me, but the front ones are a little harder to diagnose.

 

I drained the diff today. I spilled a little bit but I am fairly confident that it was underfilled. I read 1.6L of fluid is supposed to go in there and I estimated I only had about 1.2L. This probably makes sense because I only started having the noise after my 100k service where I changed all fluids. It's not like there was a major off-road breakage or something. So maybe it is simpler than I think?

Because of this, I'm not gonna take it apart just yet. I'll put it back in with the proper fluid without the front driveshaft temporarily (even though the driveshaft feels very solid) and then eventually button everything back up. The M205 is easy enough to take out without disassembling everything if it continues to be an issue.

 

FINAL UPDATE:

Alright... this is really dumb but I supposed I can't complain lol. Filled the M205 outside of the truck to exactly 1.6L shoved everything back in last night (including all axles, driveshafts, etc.). The noise is completely gone............!

PSA: make sure you actually measure how much fluid gets in your diff. I just filled until it started to spill out, but it looks like I made an error and definitely stopped too soon!

 

Great news!

 

The cheapest solution for the win!

 

If you filled me up [ to the proper fill line ] with liquor , I'd stop whining too !!

Glad it worked out on the cheap for ya !!