I agree with this 10000%. It's almost impossible for anyone to balance my tires. I've finally given up hope and put 10oz of air soft bb's in them. I've recently spent an entire day trying to get these balanced, after 5 different shops failed, and many many that wouldn't touch them, I said **** it.
Your issue certainly certainly sounds like it is a balance issue.

 

This has happened to me as well. Go in to get them balanced, and drive home with them worse than they were lol.

 

Ok, by the numbers. (Many years of CJs and that stuff here)

1) Tires: Tire separation at speed - possible. Logically this should move with the wheels. Maybe number the rims with paint pen to keep track of position? You said balance is good. How much weight did they have to add? Are some really really weighted for balance? What's their spec for 'good'? I've had some tires require a TON of weight while others didn't. Could be a bad batch of tires. Got some spare wheels you can test with? (I keep the stockers in my garage for snow tires)

2) Caster - How's your steering? Is your caster in spec? With a lift that big, you may want to add another half degree or so.

3) Steering damper - Maybe a little weak for 37s if it's stock. It could also be hiding the issue at other speeds. Sometime experiment is to pull it and see if the issue pops up at other speeds. (Carefully)

4) Tie rods/Ball Joints - Might have a loose one that's really letting go at this point. Again, this could just be starting up. A tight joint should move with some effort, but not be floppy. If you can mess with any of the linkages and get them to rotate by hand without much effort, it's time to get some service done. If you want a feel for it, stop by the auto store and ask to see one. Try to angle it by hand - it's hard work.

5) Weight distribution - One CJ I had got really bad when I put a trailer on it. The extra rear weight pulled the front higher - thus reducing caster and making things get a little wacky and head into death wobble. That 37 spare on the back may be altering the effective caster on you. Test: Remove the spare, take a drive. If you meet success, head back to #2.

6) Drive shaft - Could be the front drive shaft. I ended up putting double cardigan joints on the front of one trouble maker. The double joint reduces the angle that each joint sees, allowing smoother rotation. Test: Remove the drive shaft, take a drive.

7) Steering box - maybe the mount is loose. I had one nearly self destruct on a CJ, but it was really, really bad. This is more of a contributing factor, but the general theme is: all the parts are solidly mounted, right? Typically you'd see bad behavior at all speeds if this is an issue, but it'll show up really badly when there's a harmonic problem.

 

There's allot of good info here. I too encountered this problem a while ago but I only have 35's. Took me a long time to find the problem. I didn't see anyone mention the track bar, which was my problem, but that'll cause death wobble at lower speeds too. I needed to replace them cause the lock nut kept coming loose and had a bunch of play in the track bar because of that. I read a bunch about when going 37 the rubber bushings in the suspension parts are more prone to going bad also.

 

I'm thinking of adding the Teraflex front end HD parts. Ball joints, track bar, high steer knuckles, tie rod, drag link. Has anyone used these parts? Will it make a big difference? I inspected everything and it all looks ok to me but I'm wondering if beefing up my front end will help smooth things out with my 37's?

 

I think step 1 should be to perform another 5 tire rotation just to see if the shimmy still appears. It's not official death wobble based off your description. That 50mph seems to be the sweet spot for tire issues to show up.

 

Check your ball joints. Pretty simple to do. See how much play you have. 37's are heavy. Then I'd check all the bolts in the steering components

 

Check the tires first, as others have said tire places don't balance stuff all the time.

If its truly death wobble, Its definitely gonna be track bar related - if you've been having death wobble and you've been driving on it for a while you might have worn out other stuff like TREs on your TR and drag link or even your BJs....but that won't be the cause. You may still need to replace some of that but fix the DW first then deal with the other stuff

Since AEV lifts are usually just a bunch of brackets and factory crap, you probably have the factory track bar with some sort of raised bracket on the axle side. Pull the bolts and see if the holes are wallowed, on both ends of the track bar and the bracket itself. regardless of what you find, upgrade to the bigger bolts off northridge's site or just go to a hardware store. Torque them to spec, something like 140 ft/lb but double check. Most likely the bolts are loose, the holes are wallowed, or you may be getting deflection from the track bar itself, but this is the least likely.

DS isn't going to cause DW, steering stab is also not something you should replace, you don't need one if your jeep is set up properly. castor is taken care of by the AEV drop brackets.

Start with the most likely and cheapest, track bar, before you go throwing money at it.