Heya all, this is a question for any of you who know your vibrations...
friend of mine has a 93 jeep ZJ (grand cherokee), recently 6 inch lifted with 33s, has a vibration from 25 to 45, and is afraid to take it over 45.... says it starts as a side to side, then uncontrollable vibration, it did this before and after the lift... with 3 different sets of wheels and tires, and everything suspension is new from the pitman down... i say do motor mounts... he has already done
ball joints and hubs/wheel bearings... any input?

 

My guess is the u-joints on the driveshafts. The problem may now be magnified since after the lift the angles are more severe.

 

I'd check the u-joints, and then check the drive line angles. Might want to check tranny/transfercase mounts too.

 

my CJ-5 had that problem till I shrank the tires from 35's to 32's, I also went from 7" of lift, 4" suspention ,3" body to 3" which helped with everything from rock crowling to freeway speeds. I am now running a 2" suspention and 1" body. the drive shaft angles are back to the good range and most if not all of my vibration from my earlier stupidity is gone.

Changing the angle of the spring seats(welding). add some wedges, have a custom CV made or go back to a size that will complement your buddies ride chareristics( boy do I suck at spelling). Is 6" going to help him do anything but roll over at moab. most hard core cats are putting 6" in their rock only rigs and have 15+" of travel on each axel. these dudes also run 35's for going over large holes, cracks and the big stairs. check your angles and go have some fun...