2005 noise in AWD, goes away in 2H

[XR4Ti]

Hey guys,

I'm trying to track down a noise and am wondering if anyone ran into this before:

I've got a 2005 and almost always drive it in AWD. Lately I noticed a rumbling noise that seems to come from the driver's front corner at highway speeds (over 100kph/60mph). Sounds like driving over rough pavement.

I checked the front end contact points and everything seems tight. Tires are nearly new and look fine (I will be rotating them soon but I don't think they are the issue).

So then the other day I switched to 2WD on the fly and the noise went away. Switched back to AWD and the noise/rumbling comes back.

I did some searches and found the exact opposite (noise in 2WD, goes away in AWD).

Just wondering if anyone had a similar problem or some suggestions on what to check.

Any advice much appreciated.

2nd EDIT: Done more testing and the symptoms are indeed as above. When cruising at hwy speed in 2WD, I switch into AWD, feel a bit of a load on the truck, and the noise starts. Switch back to 2WD and the noise goes away.

I'll be reading up on the AWD system to understand how it works, but in the mean time, if someone can suggest any pointers for what could be causing noise in the AWD system, that would help. Does the front driveshaft turn when in AWD (and no slippage) or only when slippage is detected? I'm wondering if maybe the cause of the noise is the u-joints (I checked for play and couldn't find any, but they could be on the verge of seizing).

3rd EDIT: I replaced the u-joints and the noise is gone.

 

[XR4Ti]

Anyone? Can someone explain what happens when you switch from 2WD to AWD? That would help me track down the noise. Thanks.

 

[Notmyidi]

Power transfer from wheel to wheels that have the most traction

Either the front driveshaft is rubbing something in the front or youve got a cv going out

sent from my mind via of telepathy

 

[XR4Ti]

Thanks for the reply. Is the front driveshaft turning all the time in AWD?

 

[Notmyidi]

I believe so, IIRC the way power is actually transferred, since power moves to the wheel with least resistance, the brakes are applied at a certain wheel giving it higher resistance transferrring power



sent from my mind via of telepathy

 

[tsgrpr97]

Yes with traction control it should apply brake at the slipping wheel to divert power across an axle, and in awd setting the transfer case is always diverting some power but it is not "locked" in 4x4, it allows some slippage to accommodate for differences in rpm while driving on dry pavement/turning etc. When wheel slippage in the rear is detected the system increases the duty cycle to the transfer case allowing less "slop" between the front and rear. That's the way I understand it, at least.

Do you have a matching set of tires? A small difference in circumference can translate into a signifigant rpm difference between axles, which you won't notice with the front freewheeling in 2wd but since in awd your transfer case is always diverting some power to the front it will cause the two to "fight" each other.

It could be the cv joint too. Does it make any noise in a tight turning radius while in awd or 4wd?

 

[Notmyidi]

If your running different sized, tread type on a awd or a 4wd it will eventually grenade everything

sent from my mind via of telepathy

 

[XR4Ti]

About the tires -- all tires are exactly the same and have less than 10k miles on them.

I haven't noticed any noise from the CV joints. I had also checked the boots -- no sign of cracks or leakage.

Doesn't look like the driveshaft is rubbing anything. But I wonder if the U-joints are starting to go, since they can't be greased.

 

[tsgrpr97]

That's a good possibility. Cv joints can wear but I would think there should be some shaking/vibration along with that. Not just the noise. I'm assuming the second gen has a sealed hub/bearing unit too. If that was wearing, I would expect at least a small amount of play when with the wheel off of the ground. I can't say off hand the proper way to diagnose the u joints but I think its worth checking out.

 

[XR4Ti]

I checked the u-joints just by trying to find some play in the driveshaft in both axes of the joints (just like I used to do on the CJ-5s my brothers used to have). Nothing. But they remind me of the Expy's steering knuckle which, after I gave it a good dousing of a lubricant/penetrant, cured a stiff steering problem ie I get the sense it's starting to seize. I think I'll try turning it & see if anything obvious comes up.