Howl/whir from front end only in 4wd

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blnickel

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Hey all, first post here. I have a 95 K1500 with 462000 kms on it. I’m getting a loud whir or howl in the front end only when i’m in 4wd and above 30-40 km/h and it gets louder with increased speed. It’s tough to isolate since both front wheels spin well with maybe a slight worn bearing noise in the front left side?? I’ve replaced front CV axles, upper and lower ball joints inner and outer tie rods, sway bar links, front drive shaft u joints, idler arm and pitman arm in the last year. I’m thinking it’s gotta be a front wheel bearing but feel it’s a bit odd that I only hear it in 4wd. Any other suggestions?? Could it be something in the front axle or transfer case? Thx in advance!!
 

Supercharged111

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Wheel bearings and CV shafts spin in 2wd too. Is the front diff full? If so, does the oil have 462000 km on it? My first guess is either pinion bearings or differential carrier bearings in the front diff as those remain stationary in 2wd.
 

1998_K1500_Sub

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Hey all, first post here. I have a 95 K1500 with 462000 kms on it. I’m getting a loud whir or howl in the front end only when i’m in 4wd and above 30-40 km/h and it gets louder with increased speed.

When this happens, are the road conditions "firm" (dry dirt or dry pavement) or "loose / slippery" (gravel, snow, ice)?

If you're on a firm surface, the drivetrain may well be experiencing torque wind-up, which would put the entire drivetrain into a condition of very heavy load and may contribute to increased noise from one or more components (e.g., in your case, front diff bearing, hubs).
 

blnickel

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Wheel bearings and CV shafts spin in 2wd too. Is the front diff full? If so, does the oil have 462000 km on it? My first guess is either pinion bearings or differential carrier bearings in the front diff as those remain stationary in 2wd.
I changed the front diff fluid about 2 years ago, under 2000km ago. I will double check to see if it’s still full and not leaking
 

blnickel

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When this happens, are the road conditions "firm" (dry dirt or dry pavement) or "loose / slippery" (gravel, snow, ice)?

If you're on a firm surface, the drivetrain may well be experiencing torque wind-up, which would put the entire drivetrain into a condition of very heavy load and may contribute to increased noise from one or more components (e.g., in your case, front diff bearing, hubs).
It happens on loose/slippery conditions as well
 

blnickel

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So I double checked and the front diff fluid is 7000km old. Not sure if it had ever been done before that as I acquired the truck a few years ago. Anyways the level was a touch low but im not concerned as I had a leaking 4wd actuator that I recently replaced. I topped up the fluid and drained a bit for a sample as below. I’m pretty sure I can see some metal specks in the fluid but am just a hobby mechanic that has never dealt with bearing issues before. The fluid looks pretty nasty to me but not sure if that’s somewhat normal for 7000km fluid.
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Supercharged111

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Gear oil is an often neglected fluid, which is why I asked the way I did. That's straight up nasty if it only has 4,000 miles on it, but changing it again isn't likely to quiet the noise at this point.
 

blnickel

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Gear oil is an often neglected fluid, which is why I asked the way I did. That's straight up nasty if it only has 4,000 miles on it, but changing it again isn't likely to quiet the noise at this point.
I appreciate the feedback! Worth trying to change the fluid again for the cost of gear oil or not bother?
 

alignman88

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I’ve replaced the hubs on my 2013 1500 4x4 GMC when I heard/felt what I thought was a hub bearing going bad. With the front end raised I could hold one hand against the bumper while spinning the wheel and could feel the bad bearing through the bumper. Replaced the other side as well at same time. I’ve also diagnosed and replaced several 18 wheeler semi tractor front bearing assemblies when I owned my alignment shop.

In my experience a “whir” coming from a differential has been the pinion bearing/race going bad. A deeper “growl” sound was from the diff. carrier bearings, and a “whine” that changed when letting off the throttle was gear related.
 

Supercharged111

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I appreciate the feedback! Worth trying to change the fluid again for the cost of gear oil or not bother?

If you're going to take it apart and fix it, leave it. If you're going to try and live with it as long as possible, then I might change it.
 
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