hum or howl in 4wd

[Doubeleive]

this has been a historical issue on the gmt800's some of the front diff''s are just noisy period..
I experienced the same (noise in 4wd) and there was no indication of anything being bad, miles and miles and miles, always worked fine, just noisy when engaged
no metal shavings, no leaked out fluid, no play in anything, just noisy.
have not really heard of it happening on the 900's though until now.

 

[Charlie207]

this has been a historical issue on the gmt800's some of the front diff''s are just noisy period..
I experienced the same (noise in 4wd) and there was no indication of anything being bad, miles and miles and miles, always worked fine, just noisy when engaged
no metal shavings, no leaked out fluid, no play in anything, just noisy.
have not really heard of it happening on the 900's though until now.

I would have been fine with the noise in my front diff, but it was getting worse and worse, and the fluid was clearly full of bearing material - lots of sparkles accumulating after fluid replacement and almost no 4WD engagement.

I have the bad unit sitting on my workbench, and I'm not sure what to do with it. I could probably pull it most of the way apart, but I don't have a press to reassemble, or the desire currently to fire the parts-cannon at it.

 

[DaveO9]

I had my wife drive it tonight so I could sit in front pass seat and rear seat to listen. Still don't have it nailed down, but I think I can rule out t-case. It's most noticeable from driver's seat. I've got 207k with what I'm assuming are the original front hubs/bearings. If the noise isn't coming from the wheel bearings, no worse off since I should replace them anyway. If I still have it, I'll have to think about replacing the front diff with another used unit. But I am curious about the possibility of it just being a normal thing for these front diffs. It's not a super obnoxious noise. My subaru had bad rear wheel bearings when I bought it - that noise was crazy obnoxious. Most of the time in 4wd in the Tahoe, it just sounds like I'm running knobby mudder tires up front.

I'll report back after the hub replacements. Might be a month or two.

 

[DaveO9]

Ordered 2 AC Delco Gold hub assemblies, should be here on Wed. We'll see if that helps.

 

[DaveO9]

New Delco hub assemblies installed. No dice - noise unchanged. It has to be coming from the front diff. I will probably let it ride for a while - I don't use 4wd a ton, and it's usually short distances.

It was wishful thinking that new wheel bearings would solve it, I know. But I'm not disappointed I replaced them. At 200k+ I'm sure it was just a matter of time and now I have piece of mind on those crucial parts.

 

[GMCChevy]

My Z71 was making a humming noise only in 4 wheel drive mode turned out to be the front wheel bearings. After I installed new bearings the noise came back after about 5 months. So I reordered wheel bearings this time I ordered the timken the humming disappeared.

My wheel bearings had play in them but didnt make any noises until it was in 4wd mode but Eventually after driving them for a while they got worse and started humming constantly.

CV axles usually make a click-clacking noise when they go bad.

FWD cars can make that noise also under load so thats a good possibility. Chances are good it's something not directly related to the diff assembly since it was changed.