4WD Problem

[TBEXT2003]

When switching to A4WD in my 2003 TB EXT I'm hearing a banging noise from underneath the car. It feels like one is going over speed bump at high speed (like when one is approaching a toll both). I had the front differential replaced last year at the dealer. The original had an seal leak that could not be fixed. Does anyone know what is happening or perhaps guide me on how to troubleshoot this problem. No noise or problem in 2WD. Thanks.

[rodeo02]

Is the thump/bang happening when A4WD kicks in after sensing rear wheel slip? Or just when you select from 2wd to A4WD with the dash switch? A jarring feeling during wheel slip in A4WD is normal. With just switching the dash switch is odd. I'm wondering if you have something other than GM Auto-Trak II oil in the transfercase. Other oils will cause problems with the clutches in the transfercase.

Joel

[TBEXT2003]

The thump/bang is not related to a rear wheel slip. Its a continuous bang in the A4WD mode. I'm not sure what kind of oil is in the transfer case. Is there a way of telling? or should I try changing the Oil? I appreciate your help Rodeo02.

[rodeo02]

AutoTrak II will be blue in color. If it's not blue, it aint autotrak II. Unfortunately it's a dealer only oil @ ~$7/qt. You'll need 1.5qts (IIRC).

Joel

[clutch492]

you may have the wrong gear ratio in front end. Dealer may have installed the wrong ratio front differential.

[maxwedge]

Look at the dates before posting this is 3 years old, plus if that were the case it would lock up in 4wd, if it engaged at all.

[clutch492]

A post that is 3 yrs old is still very valuable when working on a 2003 vehicle. Let's not get critical of each other, let's help each other.

[jdmccright]

Old posts are valuable, but more so are timely posts. If the thread starter hasn't fixed the problem in 3 years, then his diff and transfer case would be in shreds by now, or parked all this time, or he's sold it and moved on. Max is simply suggesting to look more closely to see if a thread is still open and relevant.

That being said, not saying your post isn't a possibility, though at a dealer the mixing of ratios would be a big FUBAR. But different ratios engaging would lead to immediate damage or sudden lockup. On the other hand, if the system were trying to engage a 4wd with different ratios and the difference in spinning front and rear diffs prevented full lockup in the TC, I would expect more of a gnashing noise than a bang.

As mentioned, a slight bump feeling is normal when the A4wd engages, but a big thump and bang isn't. The fluid could be old or contaminated, or the encoder motor is malfunctioning.

[Jethro]

I good way to fix that is for the Mod to lock all the old posts so no one brings up the topic ever again. I have seen old topics come up in other forum for years without the starter even being around anymore. It doesnt bother me at all but some have their peeves.