Loud howl only in 4hi and AUTO not 2wd

[Kyleg234]

Loud howl only in 4hi and AUTO not 2wd.. HELP!

Hey guys I have a 2001 Tahoe 4wd 5.3 and when i put it in 4hi the other morning i noticed it was howling very loud. So I tried it in auto 4wd and same loud howl. I got it checked out and the mechanic said front diff was the problem but i wanted to know if anyone has had this issue also and what the problem ended up being. I just don't want to replace it and find out later it could just be a bearing or somp. Any prices it costed to fix would also be appreciated.. Thanks

 

[Jay]

Sounds like the carrier bearings. The IFS 8.25" front diff is known for having the spanner lock tabs break off, which allows the spanner adjuster to back off and release the preload on the carrier bearings. They will chew themselves up and eventually destroy the diff if you drive it too much in auto or either 4wd mode.

Check the u-joints on the front driveshaft first... try to move the shaft around as see if there is any slop. If you have access to a lift, get it in the air and run it in 4wd to see where the noise is coming from.

Just in case you don't know: The 4wd front ends have a small motor that, when in auto or 4wd, engages a lock collar to connect the passenger side axle to a stub shaft at the differential, locking the axle together so it functions like a live axle. GM does this to improve mpg and reduce wear on the differential while in 2wd... the half shafts at the wheels turn all the time, while the differential carrier and, thus, pinion and front drive shaft do not unless in auto or 4wd.

In auto mode, the transfer case is still disengaged, but the front axle is locked in, keeping the front driveshaft turning until it needs to engage the clutch pack in the transfer case for 4wd. This is why you can hear problems in the front diff even if the transfer case isn't engaging the front axle.

Had this happen quite a few times in the past. Rebuild kit with Timken bearings can be had for under $150. It's the labor that makes a rebuild $1,000+.

It's a risk, but you can try to find a good unit in a salvage yard. There's no guarantee it won't have the same problem, the IFS diff has a reputation for this problem and it's worse in the AWD versions since the diff is turning ALL the time. You can get one with 70k miles for $600 or less. Get one from a 4wd since it won't normally have the wear on it like the AWD versions do. You can use either though, just have to swap out the passenger side axle tube if you interchange.

 

[scottg918514]

What does the front diff fluid and fluid level look like?

 

[Gordy]

I have an 01 125000 kinda the same issue. My howl can be heard in 2wd not excessive but noticable to me. When I engage 4 auto it does not change, when I engage 4hi it gets a little louder, 4lo cant tell.


I thought it might be a front hub bearing because if I'm turning left like on a highway ramp it gets louder. Turn right it quiets down. But wheel hubs are tight according to mechanic who did inner tie rods, and front end alignment which I thought might be it all though no pulling or anything just thought since I never had it done would not hurt.


The front diff fluid is clean transfer is clean rear a little dirty. I have had these fluids changed, and maintained. Owned the vehicle since 01 with 19000 miles.


Mostly in 4 auto in snow or rain. Engage 4hi, and lo to keep working. Never off road.


Would thoughts be front differential here. If in park in 2wd with engine off should frondrive shaft be able to turn back and forth a little?



Gordy