Vibration at 70mph

[Fless]

So I put the 2003 Tahoe up on jack stands and noticed that with the '4-auto' button lit that the front driver tire and the back tires would rotate (but not the front passenger tire?). I tapped on the t-case encoder with a hammer and got it to shift to '2wd'. I heard the front differential motor unlock the front tires but it then went right back to '4-auto' on the button. At this point I suspect the t-case encoder motor so I removed it from the t-case and played with the dash buttons. The system intermittently would go into '2WD' and I could hear the front diff motor working but the encoder motor did not do anything. By the end of the trouble shooting the led's on the switch buttons were not lit at all. I suspect a bad connection inside the t-case encoder motor assembly and have ordered a new one. I believe the vibration and sound that was coming from the T-case area was due to going 70+ with the front tires engaged and the t-case was vibrating due to the computer trying to 'automatically' run the t-case with the t-case not responding to commands. Saturday the new encoder motor will arrive and I will install and (hopefully) any signal the computer is depending on from the t-case motor will be good again and it will shift normally out of 4-auto.

Save that old encoder motor. You can replace the range position sensor that's inside and probably have a good one for a spare.

 

[InterceptorF]

OK that is good to know! Thanks!

 

[InterceptorF]

FIXED. Replacing the encoder motor fixed the issue with the transfer case but once 4X4 was repaired there was still some noise from the from driver corner. In dealing with that I replaced both the hub assemblies and put in fresh disk pads since I was already there.
Now the transfer case shifts and works correctly and the weird vibration and noises are gone. It feels very good now.

 

[S33k3r]

Can you come fix mine now? May I ask from where you sourced your encoder motor?

 

[InterceptorF]

Can you come fix mine now? May I ask from where you sourced your encoder motor?

Ha - ya but no.. scitoo autoparts

 

[InterceptorF]

I'm having a similar issue with my 2003 tahoe LT. I replaced the transfer case in 2017 with a rebuild and last year the wife blew the transmission which I replaced with a rebuild from AAMCO which has been working great but last week the button went to "4-auto" and would not switch. I loosened the bolts on the encoder and got it to switch to 2 wheel but it went back to 4 auto after some time. Also after some time the "Check 4X4" lit on the info screen. What I am also noticing is at 70 + mph the Tahoe starts vibrating slightly and it feels like the t-case output shaft or the rear drive shaft where it connects has a slight wobble. I haven't looked any closer yet but if I let off the gas the sound its making changes. Things I am suspecting... low fluid, loose mounting bolts to trans, bad encoder motor (making the computer try to do the 'auto 4x4' stuff), failing bearing in the T-case, drive shaft out of balance or possibly the front u-joint on the rear drive shaft but I'm pretty sure I have already replaced that u-joint last winter. Any other ideas are welcome. I am hoping the T-case is just low on fluid at this point and will be looking closer in the next few days but will keep updating this post on what I find.

So I put new tires (Toyo 265/70R/16) on the 2003 Tahoe and of course balanced them. The transfer case needed a new encoder motor and now it shifts correctly. The u-joints are all new. I still have a vibration that feels like its from under the seat ( t-case area) at 70 + and with some time it seems to 'balance' and clean up but does come back - then cleans up, etc. The T-case was replaced in 2007 but the transmission blew out in 2020. I am wondering if the transmission exploding may have compromised the bearings in the transfer case. At this point I usually don't drive it faster than 50 ( to work) so I am still diagnosing and hoping I don't need to rebuild the t-case and replace its bearings. It seems fine even when going freeway speeds but I do notice the vibration. Depending on time and availability I may drop the transfer case and replace the bearings in it this summer as a last resort to get a smooth +70 mph.