I was planning on ditching the old roto flex. But I'm afraid that since the old one sheared a bolt and wollowed out the driveshaft bushing after 3000 miles I don't want to mask a bigger problem. With the car sitting in the garage the axle is tilted 4° from level. The rear prop shaft is at 8°. While the transfer case and the frame of the car sit almost level at 1°. So the difference in angle is between the transfer case and prop shaft is 7°. And 4° between the axle and prop shaft. Is that normal for a non lifted disco? Would that angle cause the issues that I'm seeing?

Backstory
Went on a road trip and on the way back home my 96 disco started shaking at speeds between 60-80mph. Felt pretty Similar to driving on a rumble strip. Any faster or slower and it more or less went away. We continued driving it 1,500 miles home and noticed that the newly replaced rotoflex had one of the bolts was missing the nut, threads, and mishapen. Upon further inspection the bushing in the end of the driveshaft had the rubber insides all wallowed out.

I haven't lifted the vehicle but i did replace all of the suspension bushings as well as the track rod and drag link. The previous owner replaced the shocks. And I recently had the transfer case and driveshafts out to get resealed and have the roto flex replaced. I didn't know better at the time and took all of the bushings out at once. After doing this the disco got a pretty bad death wobble after hitting a bump at highway speed. An alignment and tires took care of the problem. However it came out of alignment again soon after. so I'm not sure if everything needed time to settle or if I've messed something up. Firestone also didn't bother to straighten out the wheel and said they got it "as close as we could". So I'm not sure what happened there. I'm also curious to see if its still in alignment after driving with the vehicle shaking for so long.

 

It was probably a bad install on the Rotoflex. Hopefully they got the bolts on tighter and with some locking nuts or loctite.

Death wobble could be a couple things:
- Poorly balanced tires, of course. Also tire out of round. Road Force Balancing would get to the bottom of the balance/tire issue.
- Bad front shock
- Bad/Worn shock bushing (I just went through this ...lower bushing on my tk's Ft shock degraded). I put on a new lower bushing and it helped a lot. But I discovered a 'free spot' on my shocks. There is a spot where they easily move 1/2-3/4" with little resistance. So the shock need replacing. Haven't put the new shocks on yet. But just the new bushing greatly tamped down the wheel hop.
- Excess play in the wheel bearings. There should be 'some' freeplay, but not too much. I have mine adjusted to slightly less tolerance than the manual suggests ....just right, where there's just a slight amt of freeplay.
- Worn or excess 'play' at the upper/lower swivel-pin bearings/bushings. Everybody thinks this at first, but test it out (tons of how-to videos). Be sure to check out other things listed above too.

If it does the shakes when you hit a bump that kind of makes me think it's with the front shocks. A bump on the road or tar strip initiates a tire 'bounce' and the shocks cannot control it like they should and the bounce gets worse. That's what was happening on my Disco. Don't let it go on too long, it could create a permanent out-of-round issue with the tire that can't be corrected.

I've been setting my own vehicle's tow for years. Got tired of paying shops good money and not getting the steering wheel right either. Make two jigs from aluminum home-depot square-tube, and some blocks, which are straight & 'true'. Affix to wheel. Lay a tape measure front and back. Set toe about 1/16" (in) on the front. My jig is simple but it works on my fleet, for the little I need them. You don't need anti-friction plates...just make tow adjustments and rock the vehicle forward/back a foot to equalize the forces/wheels. Test drive and re-adjust as necessary. You'll be finished in the time it would have taken you to drive your Disco & drop off at the alignment shop. All my vehicles, the steering wheel is 100% "on the money" going down the road.

 

That is awesome that you do your own alignment! Sorry, my post was written out of order. The death wobble is fixed. Although when I hit a bump it does act like it might start again for half a second. Ive replaced it with a four bolt flange now. So the vibration is also gone. I'm still worried that I may have done something wrong with the driveshaft angle being that steep. I'll check out everything you mentioned as well. As I haven't looked at several things you mentioned.