Bad Bearing or ???

The Denali (AWD) has developed an interesting noise lately in the front end...here are the symptoms:

- Noticeable when coming to a stop, between 25-10MPH...not constant
- Partial throttle between 30-50 can induce the noise
- Sounds like a groan when stopping, driveline whine at PT
- Noise not existent when cold, louder when warm
- No noise when wheels "free spun" by hand on jackstands
- Wheels tight when rocked top to bottom

I'm used to a constant howl or grinding noise when a wheel bearing goes bad, but this is a different noise. Front/rear diffs and transfer case fluids have been flushed recently (noise present before and after) and brakes are fresh.

Any ideas what this could be? Hub, carrier, front diff input bearings or ???

Normally carrier bearings show themselves in the 30-50mph range at very light throttle and it's just a hum unless you drive it long enough for the bearings to start disinitigrating, then it becomes a growl and eventually a boom.

At slow speeds on decel the transmission will be downshifting and if there is any slop anywhere, be it driveline bearings or u-joints, it will cause a chatter. Wheel bearings usually show symptoms the worst when you steer while in motion. A good test is to find a parking lot and do figure 8s at 10-15mph.

I would double check the joints on the driveshaft first. Put one hand on the driveshaft and with a rubber mallet lightly rap on the shaft and yokes to feel for movement. Try wiggling the front tires again, there should be no movement since the bearings are preloaded. From there I would assume the front carrier bearings are at fault since the 8.25" IFS differential has a bad reputation for the spanner lock tabs breaking off, letting the spanner nuts back off and obliterate the preload.

FWIW, I've never had a pinion bearing go bad in these diffs, it's always been carrier bearings and every one of them had a broken spanner lock tab. Those things piss me off.

They aren't that hard to change if you have the right tools. Just a bit unusual since the front diff must be "split" to get to the carrier.

Appreciate the detailed response, Jay!

I did some more testing as per your recommendation and am ruling out the driveshaft and hubs at this point, especially since at very light throttle a hum does exist (different noise than the decel groan) and disappears when you let off. The two noises seem to be pointing directly at the carrier bearings, at least from my limited understanding of it all.

Likely I'll take it to a trusted mech to verify, but at least now I can speak somewhat intelligently about it.

Some additional questions:

- Since I recently changed the diff fluid, would I have seen the broken lock tabs on the drain magnet? There were two decent sized pieces (1/8") attached to it, but looked more like shavings...
- What are the "right tools"? I am a relatively competent DIY guy, but limited experience with trans/driveline...
- I did notice that the half shafts seem to have some play, i.e. if you rotate the inboard end back and forth slightly the outboard end does not move like I would expect it to. Normal operation or ?

Thanks!

For giggles, check your emergency brake shoes, mine went out and thought it was a bad bearing, was metal to metal and tore up my disks. Only heard at lower speeds coming to a stop.....

Definitely not the e-brakes, but I certainly appreciate the suggestion!

Having the GM techs look at it on Saturday...I'll post what I find out. Hoping they find it's just a wheel bearing...we'll see if I'm that lucky.

Be careful assuming it is coming from the front. I had a 2001 Suburban that had a noise that I swore was coming from the front. Put on new hubs, rotors, pads and spent a lot of time on it. Turned out to be a rear axle bearing. The sound was resonating through the driveshaft. Sounded like it was coming from directly in front of the brake and gas pedals.

Well, it's a carrier bearing, unfortunately...super!

Thankfully, the R&P is damage free...only one bearing is bad (i.e. "grenaded"), but odds are that all are close to being at the end of their service life and have been subject to metal floating around. Replacing them all while the case is split and everything is torn down. Amazed that a bearing would go that fast in less than two weeks...catching this early and getting it fixed is DEFINITELY the key differentiator between a <$1K job and >$2K job!!!

Should have it back today!

Thanks for posting back an update on it so that we know what the resolution was! That'll help in the future when people come back and search for this very same problem

07Burb said:

Thanks for posting back an update on it so that we know what the resolution was! That'll help in the future when people come back and search for this very same problem

Click to expand...

Absolutely!!!

Picked up the Denali this afternoon...wow, what a difference...it's like a new truck again and noise free!!!

Broken spanner nut lock tab caused it all......what a ****** design!!!