Drone under load!

Gordo

Original poster
Member
Mar 26, 2012
81
I've got an annoying "drone" from somewhere in my driveline. Sounds like tire noise but stops immediately when I let off the gas. No change when I switch from 2 to 4 wheel drive, or drop a gear in the tranny. I'm bringing it in the shop today but not sure where to start looking! Can't see it being a wheel bearing, differential maybe??
 

gmcman

Member
Dec 12, 2011
4,656
Could be an exhaust leak...I had that and my muffler had a gaping split on the top side. Did this happen all of a sudden? Have you checked the rear diff fluid or transfer case fluid? TC has a 50K change interval.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Or the exhaust manifold, especially if it gets better after warm-up.

Driveline noise can be differential, U-joints, transfer case.

How many miles, any maintenance history, and how recent were your TC and diff fluids changed?
 

Gordo

Original poster
Member
Mar 26, 2012
81
the roadie said:
Or the exhaust manifold, especially if it gets better after warm-up.

Driveline noise can be differential, U-joints, transfer case.

How many miles, any maintenance history, and how recent were your TC and diff fluids changed?

287000 Kilometers, no history on front dif or TC. Changed the rear dif last spring. Don't think it's exhaust, too high pitched, sounds like a bearing issue.
 

gmcman

Member
Dec 12, 2011
4,656
I would surely check the transfer case for fluid, use only Autotrak II fluid which is blue in color. Whatever you plan on checking, be sure you can remove the fill plug and remove that first, don't drain then try to remove the fill plug...you may be stranded, over time they become stubborn.
 

Gordo

Original poster
Member
Mar 26, 2012
81
gmcman said:
I would surely check the transfer case for fluid, use only Autotrak II fluid which is blue in color. Whatever you plan on checking, be sure you can remove the fill plug and remove that first, don't drain then try to remove the fill plug...you may be stranded, over time they become stubborn.

Had the top plug out, no problem, fluid is up, and blue! I'll visit the GM dealer in the morning and get some new stuff. Front U joint is pooched, I'll let you know if this fixes the noise!
 

gmac310

Member
Dec 4, 2011
174
I have the same problem. For me it's because I have too much backlash in my diff. I replaced the locker last year with another and had to reuse the stock shims for the carrier and ever since it has made a droning sound like you describe.
 

Gordo

Original poster
Member
Mar 26, 2012
81
Changed the front U joint rear shaft, it was pooched. Other 3 are good. Now the noise seems even more pronounced, guess cause I can't hear the ad U joint anymore.

It's on the hoist so I can run it in gear, Now seems noisier in 4H. Not bad in 2H but now it's more pronounced when I let off the gas. Opposite to when I'm driving it. I'll change the TC fluid tomorrow.
 

gmcman

Member
Dec 12, 2011
4,656
Are these factory joints or have they been changed once? You can tell generally by the little white pimple of a tap on the yoke. This is factory epoxy and needs to be heated before pressing out.

If they have been replaced, look for any absence of retainers., generally a large C-clip...shown in pic. Factory joints don't have the clips, the epoxy holds them in.
 

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Gordo

Original poster
Member
Mar 26, 2012
81
I believe U joints are all good. Got the rear dif cover off and crown and pinion gears look real good but I can see some movement on the right side bearing when I put a bar under the crown and apply a little pressure. Nothing on right side.

Trying to find some specs now on what play should be where!!
 

Gordo

Original poster
Member
Mar 26, 2012
81
Ended up being the inner race of the bearing right next to the pinion. Rollers and outer race looked perfect but the inner was shot. New pinion bearings and carrier bearings and it's FINALLY quiet!
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
Found this too late, but I had the rear u-joint failed, but still worked...just had slop in it and that caused the pinion bearings to junk themselves and i had the same drone.
 

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