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Author Topic: Front end (?) whine while driving  (Read 581 times)

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uconnjack

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Front end (?) whine while driving
« on: April 2, 2019, 10:30:06 AM »

Hi all, I was hoping for some help troubleshooting some noises coming from my 2008 Avalanche 5.3L 4x4 with 160K miles.  When the truck is in motion, starting at about 20 mph, I begin hearing a low whine/hum that gets higher pitched as speed (not RPMs) increases, although I canít say it gets too much louder with speed.  The sound is similar to bad tire/pavement noise, but pretty sure itís not that.  No grinding noises (yet), just whining, and does not get so high-pitched that I would can it squealing.  It seems to have gotten more noticeable since it started a few weeks ago.

I want to say itís coming from the front, but its so hard to say for sure the way sounds travel in the car.  Its most noticeable when accelerating and under load, and does tail off when taking the foot off the gas (or putting it into neutral), but doesnít go away immediately or completely.  The ďinterestingĒ thing is that when I put it into 4WDH, the sound seems to get a little louder and consistent, and no longer tails off when decelerating.  The sound also doesnít change when turning the wheel.   

I had a transmission rebuild last August, and there is only 15,000 miles on the truck since then.  The tranny fluid looks fine, although it may be a little high.  Both front wheel bearings were replaced 2-3 yrs ago, and the rear differential bearings were all replaced 3 yrs ago.  I have also been experiencing an occasional clunk when changing drive/reverse and sometimes during low speed gear changes which I was attributing to the slip yoke, but maybe its related.

The fact that the sound is a little worse and more consistent when 4WD is engaged makes me think itís in the front end, but I donít think its wheel bearings again since they were recently replaced and turning the car doesnít change the noise.  I would also be surprised if itís the tranny since it was recent rebuilt.  Maybe front CV joints, transfer case, front differential? 

Thanks in advance!
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JVZL1

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Re: Front end (?) whine while driving
« Reply #1 on: April 2, 2019, 12:14:07 PM »

 :wave: :welcome:

  Is your Trans still under warranty? Jack up and support the Avy. Still check your front
hubs some have problem with new hubs. Can you check the fluid in the Transfer Case, front diff?
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uconnjack

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Re: Front end (?) whine while driving
« Reply #2 on: April 2, 2019, 13:17:49 PM »

:wave: :welcome:

  Is your Trans still under warranty? Jack up and support the Avy. Still check your front
hubs some have problem with new hubs. Can you check the fluid in the Transfer Case, front diff?


No, its just out (its still within the 12-months, but out of miles by 3K).  I would still try to get the tranny place to at least diagnose, but the failure and rebuild happened in FL on vacation and I am home in CT.  I have emailed the shop with a description though to see if they have any insight/suggestions.

I doubt its the wheel bearing this time either since they are relatively new, and since the sound changes between 2WD and 4WD, is worse with load/acceleration, and doesn't change at all when turning, but I will go there again if its not obviously something else.  Ironically they were changed before because I was troubleshooting what ended up being a REAR differential bearing issue.  I am going to check/change the front diff fluid tonight, and maybe put the rear on stands to see if the noise is there when the drivetrain is engaged but truck isn't moving.
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JVZL1

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Re: Front end (?) whine while driving
« Reply #3 on: April 2, 2019, 22:11:09 PM »

   You do have your year in the post. It dose help other to help if you put in your sig.
Be sure to check you t-case fluid. Use the fluid recommended in the owners manual. Dreaded T-case rub.
 Good luck.
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uconnjack

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Re: Front end (?) whine while driving
« Reply #4 on: April 3, 2019, 12:49:02 PM »

So I did some additional troubleshooting:
 
I checked and changed the fluids in the front diff, transfer case, and rear diff.  All looked generally OK.  The front and rear differentials were a little low by maybe 1/2-3/4 qt, transfer case was just about full.   All have some gunk and very fine metal on the magnet plug, but nothing out of the ordinary and no metal flakes or shards were seen in the old fluid.  No change to the humming/whining sound in the subsequent test drive. 

I put the rear end up on stands to run it in 2WD while listening under the car, but it didn't tell me much.  Without any real load and with Stabiltrak going nuts, I couldn't recreate the sound, at least not for any sustained period.  I suspect I would need to try with all 4 off the ground (and in 4WD), or at a garage with rollers, to makeit useful.

I also tinkered with gearing some more while driving, and this is what happens with the sound:

   - In 2WD the sound is definitely present during acceleration, but winds down if decelerating or put into neutral, although doesn't go away completely.

   - In Auto4WD, the sound acts the same as in 2WD as described above.

   - In 4WDHi, the sound is a bit louder and more consistent, and does not change much or go away when decelerating or put into neutral.  And when the truck drops below 10-15 mph, I almost hear a sandpaper like sound, not real loud, but noticeable, kind of like when brake pads are nearly worn.

The whirring/humming sound certainly sounds like a bearing about to go bad, but I don't see why it would be the wheel bearings again so soon after replacement, why they would be affected by the 2WD/4WD changes, or why the sound doesn't change when turning.  Because the sound is affected by 4WD (definitely worse than in 2WD or even Auto4WD), I suspect its a bearing in the front diff or transfer case.   So to try and narrow it down before I start tearing things down, what is and is not engaged with respect to the front differential and transfer case in each of these drive settings?   

Thanks!
 
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JVZL1

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Re: Front end (?) whine while driving
« Reply #5 on: April 3, 2019, 17:10:12 PM »

  (So to try and narrow it down before I start tearing things down, what is and is not engaged with respect to the front differential and transfer case in each of these drive settings?)
 
  Iíll have look to back. What I can recall the right side front diff there is anactuator  that engages the right front axle when put 4-H or 4-low with T-case. Auto the front axle is engaged and the T-case is engaged by the computer as needed.  2-wheel the clutches in the T-Case that drive the back drive shaft.
There are more posts on this and this may help.
http://www.chevyavalanchefanclub.com/cafcna/index.php?topic=41895.0

« Last Edit: April 4, 2019, 20:02:32 PM by JVZL1 »
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marzahld

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Re: Front end (?) whine while driving
« Reply #6 on: April 3, 2019, 22:31:38 PM »

While I'm no expert, I did have to rebuild my t-case on my '03.   The noises it made were not very extreme at all... you had to really try to listen to hear the clicking of a case losing fluid (which it was in my case)
Ditto on what others have said about the wheel bearings-- check the easy stuff first.   It takes very little time to jack up a wheel and check for lateral movement (which there should be none of).  Is there any noise at all at idle?  How is your oil pressure when driving, and when you stop at red lights?
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Re: Front end (?) whine while driving
« Reply #7 on: April 4, 2019, 03:00:51 AM »

My EXT has AWD, so all of the front drive train is always under load, as opposed to a 4WD truck.

The front differential in my truck is a constantly engaged, open differential.

That being said, when my front differential was nearing it's rebuild time, there was a constant growling noise coming from under the front of the truck, regardless of turning or speed.

The growl did vary in pitch and grew somewhat louder as the speed increased.

When we changed the front differential fluid, there was quite a bit of metal shavings material on the drain plug.

I ended up having all of the internals replaced and that made a huge difference in the noises my truck made.
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uconnjack

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Re: Front end (?) whine while driving
« Reply #8 on: April 11, 2019, 14:48:14 PM »

So, in order to troubleshoot some more, I was thinking about disconnecting from the differential to see if that removes the noise.  I understand I can remove the front axles as long as I use/make some stub axles to hold the wheel together while driving, but I am not sure about taking out the front driveshaft.  I believe it bolts to the front diff so that's easy enough, but connects to the transfer case with a slip yoke.  Would there be any issue driving the truck without the front driveshaft, with the yoke/spline removed from the transfer case (e.g., fluid leakage, or is it sealed?)
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marzahld

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Re: Front end (?) whine while driving
« Reply #9 on: April 15, 2019, 11:43:31 AM »

It sounds like you've tried all the different tcase modes and listened.  I can tell you for sure that every chevy 4x4 I've ever heard makes a "pavement" type noise when the case is set to AUTO.  This noise goes away when using 2WD instead.   That's why I never use AUTO.   Since you've still got the problem in 2WD, I'm thinking your problem is not with the tcase.
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Motor7

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Re: Front end (?) whine while driving
« Reply #10 on: May 1, 2019, 06:03:19 AM »

Are you getting any vibration when off the throttle, or going downhill above 70 mph? I had the whine and that vibration. A dealership and an independent tranny shop found lots of metal in the front Dif, so I had it replaced with a re-man. Also did all U-joints on v=both driveshafts. The whine is a lower frequency now and not as loud, but the vibration is still there. I'm thinking front wheel bearing now & even if yours were replaced non oem parts might be the issue.
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Re: Front end (?) whine while driving
« Reply #11 on: May 4, 2019, 11:25:09 AM »

I have had my fair share of drive train noises and issues and the noise you are describing sounds a lot like the planetary gears in the transfer case.  My Avy was making a whining noise as you described and I thought it was the gears in the rear diff again, but it turned out to be the T-case.  Most transmission shops will give a free diagnosis and it will also be a lot less of a headache trying to track down the issue yourself AND still having to take it in for repair as well.
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uconnjack

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Re: Front end (?) whine while driving
« Reply #12 on: May 20, 2019, 18:59:25 PM »

So to dig up my older thread, I finally found some time to do the additional troubleshooting I wanted:

First, I checked the front wheels for play.  Drivers side seemed to have some slop, so I changed the wheel hub assembly.  No change in the noise.

Second, I bought two junker front axles and disassembled the CV joints to make splined "blanks".  I removed my front axles and replaced them with these blanks (to keep my wheel hub/bearings stable), essentially disconnecting my front wheels from the front differential.  No change in the noise under normal 2WD.  HOWEVER, now when I engage 4WDHi, the noise does not change at all (before it would get louder and more constant in 4WD).

Third, I removed the front drive shaft from the transfer case/front diff.  Sound was the same as above.

So since the wheel bearing replacement made no difference, and the sound was still there when totally disconnecting the front differential from all movement, it takes the front end portion of the drive train out of the picture.  This basically just leaves the transfer case, rear driveshaft, and rear diff.   

Like I said before, I rebuilt my rear diff a couple years ago, so I would be surprised if bearings went bad there again already.   Plus, when the front portion of the drive train was connected and 4WD engaged, the noise would be discernibly louder and constant.  If it was the rear portion of the drive train, I see no reason why the sound would change with 4WD engaged since the load on the rear wouldn't change.

So I am pretty sure it must be the transfer case.  I think that when the front drive train is connected, the sound gets worse in the transfer case with 4WD engaged because there is actual load added to the system.  But with the front drive train disconnected, the transfer case noise doesn't change because there is no load (its just spinning a blank yoke).

Does this logic make sense?  Any opposing opinions?  Thanks!
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