i have a 89yj with 4inch springs and 2.5 shackles i have 0 vibration ever i have stock driveshaft and just a Tc drop i had 0 vibration be4 TC drop i just fiqured i do it. i had had the universals snap on me but that was because i had a stupid mechanic put the wrong gears in my rear 307s what an idiot so offroad in ruts i was getting wheel hop from the differnt gear ratios and i guess maybe some of the angle or what ever and pop the rear snapped and i was some what out of commision. than i just pulled rear driveshaft out and went back with just front wheel drive and still did beter in the 4foot + puddles than trucks more beeded up than mine i have never gotten stuck in my truck EVER(minus it braking down) and i hope to keep it that way
I'm running 4" springs, on 33's. Definitely a lot of vibration. I'm currently looking for an SYE . *BUT* That's because I plan of doing SOA, getting a Ford 8.8 etc. etc. So.... I would spend the money if you plan on going further, but if not, just try to make it work.
When I 1st installed my 4" rc springs almost 2 yrs ago I added the drop and it didn't vibrate at all. I then added their 1" boomerang shackles and it started having vibes around 45-55mph. When I took the hardtop off then it got worse to a point 40-60mph it vibe mildly. Shortly after that I blew a ujoint at the slip yoke. Until this day it vibrates 40-50mph or under heavy acceleration. I need a sye. Minimum lift without a sye to me is 3.5-4" lift anything higher than that you need to look into investing a sye.
"Its a Jeeps World, other 4x4s just get stuck in it."