I have an 02 denali AWD, 138k miles (owned since 67k).

Recently I took two road trips back to back, and noticed afterward that I had developed a new noise/vibration sensation in (what seems to be) the front end.

When driving under load or accelerating everything is fine. If I am anywhere between say 30 and 50mph, and ease off the throttle to cruise (neither accel nor decel) then after about 2-4 seconds, I will hear and feel this grinding vibration sensation which seems to come from the front drivers side area. As SOON as I apply any amount of throttle, the noise and sensation go completely away. So, the problem is both speed and load dependent, but it's not 100% consistent. Sometimes it'll go for a few minutes without doing it, sometimes it's repeatable several times in a row. It doesn't seem to respond to changes in steering or braking at all.

I've already replaced both front wheel bearings about 50k miles ago. Both are perfectly tight when I try the 6 and 12 oclock test.

I've already replaced both front shaft ujoints about the same time. Both feel normal to me with no excess play in the joints.

I inspected the drivetrain and found (what I thought was) excess play in the transfer case's front output, where the front shaft goes into the case. I could wiggle about 1/8" or so there. So, I figure bearings have gone bad and maybe that is the cause of the noise. I tear the tcase out and replace ALL the bearings with an overhaul kit. Put it back together, put it in. Still have same amount of play in front output shaft. Noise/vibration still present.

Next I move up to the front diff, notice a slight oil leak on the driver output flange. Then I notice that I have about 1/16-1/8" play in that flange. So I read up online, find that the denali/escalade/SSS awd diffs are problematic, and assume that I have one or more bad bearings in mine. I drain the diff fluid which I switched to mobil 1 synthetic 20k ago, only to find that it is dark colored with metal particles on the magnet. I remove it, tear it down, sure enough, the diff carrier bearing races are a little worn in spots. So I order an overhaul kit and replace every bearing and seal and set all specs as perfectly as I can. Reassemble, reinstall, fill with fresh mobil 1 synthetic. Play in output flange is gone. Road test...noise and vibration still present.

Now I'm down to replacing parts that I've already replaced and inspected, and seem fine: front shaft ujoints, or front wheel bearings.

Or maybe, this is a shot in the dark, front cv shafts? One is a reman, one is original, both have intact boots and make no noises when making tight turns or accelerating from a stop (which in my experience are the indicators for a bad axle).

Pretty much everything on the suspension is new...all moog front suspension joints, brakes in perfect shape just done 25k miles ago.

Any ideas or experiences?

 

Without first hand checking it out. Left front wheel bearing or maybe something in the Tcase beginning to frag on you.

 

Thanks for the reply, but...

 

You mention vibration, check the idler and pitman arm, along with the front shocks. Also, make sure you don't have a sticky brake caliper, that may be your grinding. You may have already thought about this, but it's a shot in the dark. You have pretty much ruled out everything else, and you are correct about the carrier bearings about being a problem.

 

With today's quality it wouldn't be the first time I've had a new replacement wheel bearing that failed come through the shop. I've had it happen even on gm bearings we have installed as of late.

Did you check the inside brake pad to see if it could have shotgunned the friction material only.

 

When the U-joints were replaced, are you 100% sure they were replaced in the same position?

When a shaft is balanced, it needs to stay in that position, or it needs to be balanced again. A yoke could be installed 180 degrees off, and it would make the shaft out of balance.

 

Thanks for the reply. Idler and pitman arms, as well as all balljoints and tierod ends, are new Moog components about 1 year old.

The term "vibration" may not be totally accurate. But, when the noise in the front starts, I feel a very slight sensation in the floorboard...as though somewhere underneath, something still connected to the truck is dragging the ground. So a subtle feeling, but I can feel it come and go with the noise.

How would front shocks produce a speed and load dependent sound?


Load dependent with throttle application?

 

That's what I am kind of thinking. The front right is about 50k miles old since I replaced it. I actually removed it from the truck so that I could spin it and feel for any binding or tight spots. It rotates pretty freely and doesn't make any noises or have any uneven spots in it's rotation.

I also can't figure out why a wheel bearing would produce load dependent noise that varies with throttle application. The noise doesn't seem to increase or decrease as I go around curves, which also doesn't suggest a wheel bearing.

The pads and rotor looked normal enough when I had them off to get at the wheel bearing.

Two of the brake calipers have been replaced at one point due to broken bleed valves, and the other two were in good working order last time they were inspected.

There are so many new or rebuilt parts on this truck it's not even funny. Literally the transmission and rear diff are the only original/untouched major parts/systems on the truck.

 

Well, on the front shaft, there is only one yoke, that mates with the transfer case output shaft via a spline shaft that has many different possible installation positions due to all the splines. The other ujoint mates directly to the front diff.

To answer your question, no, I didn't mark anything as far as the relationship between the shaft and diff/tcase any of the several times the shaft has been removed from them.

But also note that this problem originated recently, and no new work had been done to the shaft or any drivetrain parts in about 20k miles. So I don't see how suddenly it would decide that it was out of balance.

I am however thinking of replacing those ujoints again just for the hell of it, since they are only like 37 bucks for the pair.

 

the shock will cause vibration in the steering, not a noise. Try pulling the abs fuse to see if maybe the awd is engaging when it shouldn't be. Mine uses the BW TC that utilizes the abs system to route traction. I think you may have the NVG 149 TC being an 02, if so, disregard, but it could be the viscous coupling in the TC. Does it pull to the left or right?