4x4 problem on my Avalanche

[Buoy]

I have a 2004 Av 2500 with the 8.1. LOVE the truck, but having a problem with the front end.
~67K mileage, and always maintained.
Usually leave the 4x4 selector in the mode that let's it self select between 2 or 4 wd. (I need 4x4 just to get in/out of my driveway)
At low speed turns I'm getting noise (parking lots), and it almost feels like having a tandem axle trailer that you backed into a 90 degree angle, and have to "drag" the axle to straighten it out. Kinda like it's hopping across the pavement.
Seems to be fine if I manually put it in 2x only.
Any thoughts??
Electrical at the switch? Slip/clutch in the differential?
It's gonna need to go to the shop, but just want to get some suggestions, and not get BS'd into a 10K bill at the shop:grumble:

 

[ChevelleSB406]

Sounds like something is screwy and its scrubbing the inside tire in the turn. I worked at a chevy lot before my days with Caddy and noticed this with H2's as they didn't have that "Auto 4wd" option and just had 4 hi 2 Hi and 4 Lo that year. I would guess it is thinking it should be in 4 hi and lock the front diff out, or your e locker on the rear is "thinking" the same thing. I am sure someone more in the know will chime in.

 

[Buoy]

Sounds like something is screwy and its scrubbing the inside tire in the turn. I worked at a chevy lot before my days with Caddy and noticed this with H2's as they didn't have that "Auto 4wd" option and just had 4 hi 2 Hi and 4 Lo that year. I would guess it is thinking it should be in 4 hi and lock the front diff out, or your e locker on the rear is "thinking" the same thing. I am sure someone more in the know will chime in.

That's kinda what i'm thinking.
Something in the "brain".
Right hand doesn't know what the left is doing sorta deal.
Im not a mechanical idiot, but this is beyond me, and want to get it taken care of before it tears up something else.
Just want any ideas of what to look for.

 

[SBMech]

Some notes I found :

While operating 4WD vehicles in the 2HI mode they should perform similarly to an equivalent 2WD version of the vehicle. However there are still additional components on the vehicles and there may still be some slight differences in characteristics. Some Part-Time 4WD transfer cases may make a slight gear rattle type of noise when operated in 2HI at low engine speeds similar to a manual transmission gear rattle type of noise. This can originate in the synchronizer assembly from engine harmonics. This noise will usually be reduced or eliminated while driving in a 4WD mode because the synchronizer assembly clearances will be taken up once engaged in 4WD. Operating the engine at a slightly higher rpm should reduce this noise.

While a vehicle is traveling down the road the tires rotate a certain number of times per mile depending on the true tire radius. If all the tires do not have the exact same true radius (due to load tire pressure wear build variances...) they will turn at slightly different rates. Also unless the vehicle is traveling in a perfectly straight line the front and rear axles are traveling in a slightly different arc which means the front and rear axles are traveling at slightly different average speeds.

These systems either do not have a center differential or it has been bypassed (when used in 4HI or 4L0 in Part-Time or Automatic systems or 4HI Lock or 4L0 Lock on Full-time 4WD) so the front and the rear propeller shafts will turn at the same speed which leads to the front and rear axles rotating at the same average speed. Using the 4WD modes (4HI, 4L0, 4HI Lock 4L0 Lock) will usually increase noise in the axles transfer case and the rest of the driveline and is usually greater at higher speeds and will usually increase the more the vehicle is turned. As the vehicle turns the front and rear axles follow a different arc. when this occurs the only place to compensate for this binding is between the contact patch of the tires and the ground. This can feel like the vehicle is vibrating crow hopping or grabbing. Even if the vehicle is driven in a straight line there are slight differences in tire circumference that will cause some driveline binding. If a vehicle had the exact same size tires and was driven in a perfectly straight line the fact that more parts are moving would mean that there would be more noise and possibly some feel of the system operating.

Use of 4HI or 4L0 and 4HI Lock or 4L0 Lock on Full-time 4WD is intended for use on a low traction surface such as snow ice mud or sand. On a low traction surface the differences in front and rear axle speeds will not have as much effect on binding because of the lower traction levels between the surface and the contact patch of the tires. On a high traction surface the higher traction levels will create more binding and noise in the driveline.

Tires are important too:
TIRES

Tire rolling rates can be a major factor in operational characteristics. Consider the following important items:

All tires are the same size and brand. Tires of different brands may have different circumferences (or radius) even if they are the same size.

Tires are set to factory recommended pressures. A tire with low air pressure will roll at a different rate.

All tires have approximately equal amounts of wear. Tires with different amounts of wear will roll at different rates.

All tires are the same tread type. Don't mix on-off road all-season or street tires on the same truck as they may have different circumferences and roll at different rates.

Sounds like you may have an issue with the autolocking feature not disengaging, the clutches may be worn or binding. I would guesstimate around 3-400 to start, some of the control motors can get really spendy if it's not just a one way clutch worn out. Could easily get into the 2-3k range if something is really wrong, but not even close to 10k

What happens if you force it manually into 2hi? Does it still feel like it's stuck in 4wd?

 

[Buoy]

It's all push button electric shifting on the dash, so I don't feel anything.
I'm not very knowledgable about how the front end of 4x works. I was thinking like a "limited slip" diff.
But, that's why I'm asking here.
Tires are not an issue. All new about 10k miles ago.
Obviously my $10k repair was an exaggeration, but just trying to get an idea of elect vs. mech problem.
I plan on keeping this truck for a long time, haven't seen anything else I'd rather be driving. 3/4 ton luxury truck

 

[Deleted Account]

Almost sounds like the front diff is locking up. Does is do this the worst the tighter you turn? I would throw it into 2WD and only use the selector for home driveway use until you figure it out.

I have seen a ton of blown up H2 frontends out on the trails...

 

[Buoy]

Almost sounds like the front diff is locking up. Does is do this the worst the tighter you turn? I would throw it into 2WD and only use the selector for home driveway use until you figure it out.

I have seen a ton of blown up H2 frontends out on the trails...

Exactly.
Tight turns are the worst, but it's also intermittent, sometimes worse than others.
I run a lot of dirt roads living out here, don't know if dust could also be an issue

All this mention of H2's... My wife has a H3, should I expect a problem there as well?

 

[pronstar]

I highly doubt you have a front differential - its open so left-right rotational differences don't matter.

What you're feeling is a transfer case issue. It lacks a center differential, so it needs to unlock to account for rotational differences between the front and rear wheels. If its not automatically unlocking correctly, then you get scrub, just like putting a 4wd truck into 4wd and driving on pavement.

I would get it checked out ASAP, and drive in 2wd as much as possible until you do.


2 Tapatalk 1 Cup

 

[SBMech]

Actually it does have a diff in the front, all 4wd have either a transaxle or a front differential. Depending on the options he could have a full locker as well, it was an option.

Your switch should have a setting for 4hi, 2hi, auto, and 4low, right?

Take it off auto, try manually forcing it into 2hi, see if it makes a difference. Try manually selecting 2hi and reverse it for 20 feet to roll out the locking hub.

There was a transfer case fluid change in 2008, manditory for all systems to be upgraded to the new synthetic transfercase fluid, NOT DEX 6.

There are one way clutches in the auto locking hubs that can go bad if not lubricated or be activated by a bad wheel bearing etc, get it in asap if you still feel it binding, it will only cost you more the worse it gets.

 

[pronstar]

Actually it does have a diff in the front, all 4wd have either a transaxle or a front differential. Depending on the options he could have a full locker as well, it was an option.

Yeah, but it's an open front diff so you don't have rotational issues to worry about.
And he has a traditional tranny location (behind the engine), no transaxle.

Very few 4WD vehicles have limited-slip or locker-type diffs in the front, usually hard-core vehicles which the Avalanche is not.
I'd be surprised if it even has LSD in the rear, most are open in the rear as well.

If he has 4Hi/4Lo, then he has a transfer case instead of a center differential.
And that's where the binding is happening, and also why it goes away when he locks it into 2WD :thumbsup

 

[RivrKD]

TRADE IT IN FOR A FORD. THE AV IS TUPAWARE!!!!

 

[Zaairman]

Sounds like the typical Chebby issues of the transfercase randomly shifting into 4x4. Buddies of mine did it at 70 MPH... bnag!

 

[FreeBird236]

Engine usually has to run before you can have a transfercase problem....

 

[Buoy]

The 4x vs2x shifting is all done by the switch on the dash (elec. push button), so I can't "feel" what it's doing.
Agreed, typically an Av is not a "hardcore" truck, but mine is a 3/4 ton (only made for three years) and specifically why I bought it. I'm thinking it might be a bit more "hardcore" than the soccer-mom version.
And don't even start the fucking ford/Chevy war... That's a waste of breath.
I like the truck, and I'll run it until the wheels fall off, hell, I'll probably just put them back on.
I appreciate all the replies - even the ones that are going a bit over my head.

 

[Hugh Jascaulk]

That tranny has a known problem with the transfer case. Check the fluid level. The gear inside rubs in the case and eventually wears a pin hole in the case.
Kennedy Diesel sells a fix for this problem, hope it's not to late.