Rough ride at highway speed; feels like imbalance
 

I've got a 4x4 2-door Blazer that has an imbalance feeling at highway speed. It's certainly not subtle. Feels like the front wheels are driving over rumble strips. It's not noticeable at in-town speeds, but once its above 55, well, I hope you like your drinks shaken and not stirred.
I've commented on this shimmy/shake problem numerous times before any I've spent the past 3 years troubleshooting this. I've tried narrowing it down to several things like wheel balance to suspension. Since then it has new tires: all perfectly balanced; rebuilt suspension: ball joints, tie rods, bushings, shocks, the works basically; wheels hubs, and CV axles.

The only thing I haven't thrown the part cannon at yet is u-joints, but I don't think mine are bad. Using a pry bar, I don't feel any play in u-joints. Also I don't feel the vibration is in the chasis. Definitely 4x4 front end. But what else can I check and replace?
Is there anything on the front differential I should look into? I'm unfamiliar with what all the probable front axel components are that would create these symtoms.

I should also add that it does make an awful grinding noise when making turns while torque is not being applied. Been trying to solve this symptom for a long time. It sounds like a wheel bearing, but all 4 wheel bearings/hubs have been replaced (unless maybe I installed a defective component). I have no clue what this noise is. I assume it's something internal to the front diff, but I'm not familiar with the mechanism to know what it could be.

Do you have any uneven tire wear like cupping? With one front tire off the ground how is the side to side play?

George

On the old tires there was cupping. That's what prompted me to rebuild the suspension and such back in 2018. There's no cupping, yet, on these new tires.
Side-to-side play doesn't feel "terrible". I don't think it's "amazingly solid", but not "terrible". I don't quite have the experience with these sort of "feel" things so I recorded a few videos.

Driver side
Angle 1
https://www.dropbox.com/s/zdtv5rx5mz...12156.mp4?dl=0
Angle 2
https://www.dropbox.com/s/fee394jwu0...59258.mp4?dl=0
Angle 3 (fast forward to last quarter of the video as I am futzing around with getting the phone camera to stay still)
https://www.dropbox.com/s/90irnyc5ee...53589.mp4?dl=0

Passenger side
https://www.dropbox.com/s/nzzpzghn7l...49360.mp4?dl=0

I stopped short on the passenger side, because upon review I noticed a few things going on with the driver side.
Inner tie rod seems loose in angle 2. I know it's not because I pulled the cotter pin and checked it it with a wrench. For good measure I torqued it one more notch on the castle nut and installed a new cotter pin.
The pitman arm also seems loose. Checked it with a wrench too and it's good.
Afterwards I made sure all the boots were fully packed with grease which did help reduce the side-to-side play some. I had just greased everything, too, last oil change about 1500 miles ago.

Lets get one thing out of the way, I am not a 4x4 guy. Never owned one, never even worked on one. That said:

Its hard to say from those videos but you may have too much play in that steering system. Is that side to side play clunking or squishy? Chevy oem idler arms are notoriously bad as an example. Then there's steering box, pitman arm, tie rod ends (I think you did those). When my idler arm went bad on this and other Chevys I had all kinds of road shimmy but it almost always cups the tires. My Blazer has 200K miles and needs ball joints and shocks but what got mine going was a loose idler arm. Put in a big overbuilt Moog, set the toe in with painter tape and a tape measure (check this too) and I'm solid. Another thing that can get you going into sympathetic vibration are wheels or tires that are out of round. With the wheel off the ground lay on your back, rotate and watch the wheel lip and then the tire for lateral runout or vertical hop. Sometimes I set up a runout gauge or at least a straight edge. I just put those tires on my GMC Sierra and they are the smoothest tires I have ever put on a truck but who knows ...? If the 4 wheels are OOR and get in just the right orientation with a loose idler arm you can really get dancing at the right speed. And dude, edit those videos on your iphone, just takes 30 sec to cut out the ends, I got sea sick.


George

Have you checked the bushings on the control arms? I had the same problem and it took some time and parts to nail it down!

Is it a rythmic vibration, like a light wohwohwohwoh almost like driving on uneven tires but instead seems to come more from the center of the vehicle? Increases and decreases with speed?

Have you checked the front driveshaft? My blazer and my moms jimmy had a light sounds like that, turned out the front driveshaft was shot, not the ujoint, but the cvaxle looking side of it that attaches to the case...

Sorry I didn't read through the thread to see...