4x4 Hi Problem, Z71s Better Check This Out

Okay everyone,
After being dormant for a while, I have something to share.

If I place my Av in 4x4 hi, driving in a straight line, then brake normally to come to a stop, I will hear a resonating moan and grinding/rubbing sound coming from the front axle at slow speeds all the way up to a stop.
It does not happen in 2hi or 4x4 auto, only when the transfer case is engaged. I am not turning on dry pavement, only moving in a straight line.
My truck has 30,000 miles and only started doing this recently. I engage my 4x4 in straight lines periodically to keep the lube agitated and check for abnormal behavior. The dealer put the ears on the truck and is sure the noise is coming from the front axle, and took apart the front axle, replaced the axle races and bearings, checked the pinion gears, removed and disassembled the transfer case, put a newer blue colored fluid in the transfer case, and the noise is exactly the same. They stated that the clutches and gears in both parts looked new, no abnormal wear whatsoever.
I went for a ride this morning with the Service Advisor in another customers Z71 with the same mileage as mine, and it makes the same exact noise under the same exact conditions. They are in agreement that this sound is nothing that a 4x4 vehicle should make, but cannot find the cause. The TAC has had them check obvious areas for the cause, but no help there. The dealer is now contacting the GM Field Engineer to come out to ascertain the cause.
If any of you have a 4x4 with 25,000 miles or more, I urge you to check it out and reply here. I will post results as I get them from GM.

Check front or rear differentials. My Avalanche was doing this and it turned out to be my REAR differential. Yes, the noise was clearly coming from the front but repair to the rear made the difference.

Hey, I just work here...

Thanks Chief,
Did it happen in the rear only when 4x4 was engaged? The dealer also told me they had the ears on twice, and both times stated it was definitely the front. Is it easy for them to miss that?

It sounds similar to the sound that I am geting with a truck that only had 100 miles on it. But my truck makes the same noise in 2 hi as well.

Ahhnuld,,,

I have heard that the front prop shaft needs to be removed, and splines, cleaned, and re-lubed with the special prop shaft spline grease, (12345879 / page 7-24 of owners manual) or noise/binding will occur after some time/mileage... Did they perform this service? ... It's only on autotrac systems for the front, and rear on some 2wd models ... A way to tell if this is happening, is to come to an abrupt stop like HARD without activating anti-lock (put the driveline in a forward bind), and hold the brake tight the whole time... Once the truck brakes hard, and settles, take the slack from the driveline, then jump on the gas, and see if the driveline makes a "thunk" sound... That's a tell tale sign of the prop shaft splines getting dry... It doesn't sound like this, but worth mentioning...

11H

Hey 11H,
Thanks for your info, but its not the same issue. If yours is a Z71, please try driving in 4x4 hi at around 10-20 mph, driving in a straight line, then brake normally to come to a stop. I would like to know if others are gettingthe same grinding/rubbing noise. It is very noticable and obvious if you hear it.

I would like to see if we have others with the same issue before the GM Engineer shows up next Monday. You would not know you have this noise unless you drove in 4x4 hi frequently, or try exactly what I mentioned. As I stated, I drove in another customers av at the dealer and his has the same mileage as mine, and makes the exact same noise.

ok ya'll,
Here is another thread started that has similar symptoms to mine. Front Differential Problem

I know there are a bunch of you with Z71s. Please go try my suggestion. You can do it in a parking lot at work as you leave. I am sharing the information from this guys dealer with mine, and we have a GM Field Engineer who is looking at mine. I am willing to bet there are more of you who may have this issue, but don't know because you don't use the 4x4 a great deal.

I tested mine last night and didn't have any problems - Also my front diff and transfer case have both been rebuilt, so my problem might have been fixed already.

Good Luck Ahhnuld

No problems here.

Soul

This was the same problem I had with my Jeep. I needed a new transfer case. THat's when all my problems with the Jeep started.

I'd bring it in to the shop

Once again, I recieved an unacceptable answer from GM Corp.
The engineers are aware of my issue, and the statement is" We have no fix available for your problem". They acknowledge that it is a issue, but will let me know if they come up with something. To add insult to injury, if They happen to pull a fix out of their a$$ after I cross the ol 36,000 mile point of no return, they won't even promise to cover me, even though I opened this case a month ago, and well before the limit.
They also stated that there is a "concern" with the 2002 4x4 Av's, so I know there must be more out there that are doing this.
I gotta hand it to you die hard Chevy fans, yours is the patience of Job.
Can't say I will be sampling any more of the "fine crafting" that GM puts out in the future. I had a chance to Lemon law my truck a year ago, but gave them ample opportunity to finally get it right, and this is my reward for showing any loyalty. About the only thing left is filing a BBB complaint. I do have to give my shop kudos, they are really trying to help me. Unfortunately, they are tied up by the crap that GM Corp. mandates.
As I mentioned to Chief in a conversation, this truck is a great idea, poorly executed. Defintely a love/hate relationship.

Keep in mind that the AV is a Suburban chassis, including the drivetrain. If the AV has the problem I would think that the Sub also has it, and the Silverado and GMC PUs probably also.

i had the same problem and i got techs in from mich. and they figured out that it was because they put an aluminum housing on the fromt diff and when the spider gears were under high pressure that they chatter a littel bit and that is what we here. they said that this happens in the reat also but the steel housing quiets it down. i finnaly got mine to stop makeing this noise by puting lucas gear oil stabiliser in the fluid and it quit! good luck!

AAAHHHHH!!!
I'm not insane. Someone else not only has it, but has a fix. Thank you Stoodge!!!
I sent you a PM with some questions.

Thanks again,

Ahhnuld

I tried this on mine, and suprisedly did not have any symptoms....

stoodge said:

i had the same problem and i got techs in from mich. and they figured out that it was because they put an aluminum housing on the fromt diff and when the spider gears were under high pressure that they chatter a littel bit and that is what we here. they said that this happens in the reat also but the steel housing quiets it down. i finnaly got mine to stop makeing this noise by puting lucas gear oil stabiliser in the fluid and it quit! good luck!

Click to expand...

Like most others I have noticed no symptoms. My AV only 15K miles, so this thread is a great heads for things that may come. Good job stoodge!!!

One questoion: What made you look at and use Lucas Gear Oil Stabaliser?

Thanks again for your input!