Vibration /grinding at front for few seconds when hitting bump

[LikeEnvoy]

On my 2007 Envoy 4WD I have an intermittent problem - while driving along ( I think its when I hit a bump too), a sudden vibration/grinding noise starts; It seem like at the front and low down; almost like ABS grinding but no feeling through the pedal when I brake.
No feeling in steering wheel or accelerator pedal either- just the noise.
The first time it happened it was quite noisy/rough and I braked quickly in case something was falling out. The noise only stopped when the car stopped. After a thinking session I started moving again and no noise- all was fine.
It was fine until a few days later; same thing - I immediately braked and the noise stopped. Again about five minutes later and I pulled over and the noise stopped- all was fine when I moved away.
A week went by then it happened again but this time not as loud. The noise stopped even while I was slowing down. A week later- the noise started again when I hit a bump in the road (most roads in Winnipeg are bumpy) I almost didn't hear it because it was not as loud and the general road noise/traffic masked it, but I recognised it nonetheless; this time it stopped after a few seconds even before I could brake much and so I continued driving.
It has recently done it a few times, maybe about a week apart, and stops on its own a few seconds later while I start braking.
Its very intermittent so difficult to track down.
I am considering:
one of the front axle shafts (with CV joints), because if I grab the inner end and rock up and down there is play with a clank sound - although no noise when driving and no play in rotation and no clicking from the CV joints - is that normal? (No play at outer ends)
Also maybe the front differential? However - wouldn't it make the noise all the time?

It still seems like a bump triggers something, then it stops after a few seconds, so can't be bad, can it?
Maybe even the cooling fan bearing? Some members have mentioned vibration from that, although surely that would give a continuous noise, wouldn't it?

The front differential rear seal has a slight sweat/leak but nothing bad- the fluid does not drip onto the garage floor for example. 4WD works fine when I use it and I have had regular scheduled fluid changes whenever I take the car in for oil change.

I also read about wheel sensors maybe being dirty or having corroded connector pins and causing ABS to kick in on its own, but then wouldn't the brake pedal feel like the ABS was operating? It doesn't.

Maybe someone has had exactly this issue and solved it?

 

[Mooseman]

When you say there's play at the axle, is it going into the disconnect? It could be responsible if its bearings have worn out and there is excessive play. Could be making the noise when you hit a bump and the axle moves. The grease inside could be dried out.

 

[Tiggerr]

The issue you refer to about the abs and wheel bearing happens when braking at low speed...don't think that's your issue...
have you looked over your struts/mounts real well and the brake dust shields, bushings, end links? The usual suspects for front end noises

 

[LikeEnvoy]

OK, agreed, I'll rule out the ABS system. Must be in the front drive system.
I have front struts, end links (and ball joints, just in case) on order because I replaced the rear parts and found one shock totally slack and the other weak; replacing those improved the rear a lot, so that together with the mileage indicates it's time to replace the front struts etc. (ride has been very hard over bumps)
The front drive axles: outer ends are solid, no play; but at the inner ends where the large metal tubes are, with the three depressed lobes in them, (passenger side goes into the disconnect mechanism and driver side goes into the differential casing), if I grasp them firmly and heave up and down, they move up and down.
The driver side only moves a small bit and is silent as it moves but the passenger side moves quite a bit and makes a 'clank' sound as it hits uppermost and lowermost limits. It seems like this is bad and they shouldn't move at all. I just found this thread:
http://gmtnation.com/forums/threads/4wd-acting-odd-intermittent-service-light.16557/#post-524167 ......

"Another thing to check is for slop where the passenger side CV axles goes into the disconnect on the side of the oil pan. If there is more than a slight wiggle, the disconnect is worn."

So the fact that the passenger inner end moves up and down a lot more seems to indicate it's the disconnect that is allowing the play, right?
Today I did a test. First I checked the front differential oil level was ok then I jacked up the front end on axle stands and with engine running I found this: in 2WD each front wheel rotates independently, freely with no clicking and no stiffness (except passenger wheel started out having a stiffer spot at one part of the rotation but that was due to the brake caliper; once I pushed the caliper in and out a bit it freed up).
Then I switched to 4WD and tried turning a wheel again. Each wheel still turned independently, so I learned that the car must move, i.e. the front differential must have to turn so that the axle disconnect will line up and engage.
So I lowered it and drove forward and back slowly, then jacked up onto the axle stands again. Now rotating one wheel produced opposite rotation in the other wheel. I suppose this is how it should work due to the differential gearing. Can you confirm this behaviour of the disconnect etc. sounds right?

So what about the movement I described in the inner cv joints; do you agree it sound like the driver side is normal but the passenger-side has too much play and it's likely the disconnect bearing, as the quoted piece said, and as you suggested?

The car switches into 4WD hi and lo and 2WD cleanly and drives ok in all modes and the grinding noise /vibration is only intermittent. There is no clicking or rattling from the cv joints, either in turns or a straight line.
Mind you, for a couple of years I have heard a 'clank' sound when I go over some types of bumps, seemingly from the back, but maybe it's not from the back after all; maybe the play and clank from that passenger-side cv /disconnect travels along the car and that's what I have heard all this time.

New disconnects seem to be at least CDN$600 on the internet and more like $1500 in local store list prices! Ouch!

 

[LikeEnvoy]

p.s. this thread : http://gmtnation.com/forums/threads/weird-vibration.7260/ may be a similar issue.

 

[LikeEnvoy]

Solved- Yes it was the 4WD disconnect. Car was off the road for a month while the part came from USA- first one was stolen/lost by the time it arrived at the global shipping depot; second one arrived ok .

P.S. GM Canada wanted $1500 for it but that was irrelevant because they have discontinued it! The USA has loads of them so I ordered from APDTY via eBay and got a new oem part, fully greased and with protective caps in the bearings.
So, new bearing, new CV axles (one was damaged by the broken bearing and both were a bit jerky when I flexed the joints off the car; new ones flexed smoothly), new ball joints and sway bar end-links and new front struts- it rides nicely now (at least on decent roads out of province; most roads in Manitoba are like third world tracks so the car is being punished on every trip).

 

[Jeffrey gray]

I seem to have the same problem when going over bumps. It sounds like a rattle in the front end but I’ve replaced everything except the axles and diff bearings. I’m planning on replacing the rear as well but it seems to be the same sound you’re dealing with. I’m replacing the axles and bearings and rear suspension to eliminate any other issues. 180,000 miles and I’m replacing all the suspension components and lifting it 2” in the back and 3” in front with 33” tires. My question is...what exactly did you replace to end the rattle in the front end?

 

[Mooseman]

He replaced the disconnect.

 

[Jeffrey gray]

I’m a little new to this platform and im wondering what the disconnect is? Sorry for my ignorance.

Ok. Excuse me for my reply without doing my homework. I found out what the disconnect is.

[Mod edit: posts merged. Please edit you last post if within 10 minutes instead of posting consecutively. Thanks.]

 

[LikeEnvoy]

Yes, as Mooseman said, it was the 4WD disconnect (aka intermediate shaft bearing assembly). The outer bearing was shot.
There is a lot of good info on this site, so it's worth looking a bit to find all the relevant information. You'll see from other info that this assembly fits on the passenger side of the front differential casing and the passenger front wheel cv axle rides in it.