Hi, all!
I am at my wit’s end with this thing. I drive a 2008 Suburban LS. It’s the 5.3L flex. I recently had the oil pump, timing chain, and a few other things replaced and it runs better than it has in years.....while in 2WD. As soon as I put it in 4WD high and get up to 20-25 mph the whole front end shimmies and shakes. I switched it back to 2WD and all of it goes away. Being that it has 193k miles on it, I figured drop the front differential and it was time for a rebuild anyway. All new bearings and races throughout the diff. Got it put back together and back in. Went ahead and replaced the u joints on the front drive shaft. Already had one end disconnected and they were the original u joints, so made sense to go ahead and swap them out. One of them was in pretty rough shape, so was just a matter of not very much time on it. Wrapped it all up yesterday and test drove it. The shaking was gone for my test drive, but I was getting a “service 4WD” on the DIC. Got back home and ran a scan on it. It was throwing a C0379 code. I pulled the actuator out and tested that, and it works fine. Put the actuator back in and test drove it tonight and the shakes and shimmies at 20 mph are back. I know I still need to go check to see if I’m getting voltage where I should on the harness and continuity like I should.

Does anyone have any other suggestions of what on earth I should check? I’m super frustrated!
Thanks!

 

Check the hub bearings, sometimes they can be loose but not make any sounds.
CV's loose or not binding ?
4wd will bring out any looseness in the front steering like tie rod ends, etc. .
Maybe actuator is only partially shifting ?
Just a few suggestions, good luck.