Vibe question w/research

[Ragtopman]

Ok here we go 91 YJ 4.0l 5spd just installed a 3" rough country lift with 1" shackles, and dropkit installed. I get a vibration between 48 and 53ish mph smooth on the highway at 70. I have read the posts about transfercase output and axle output being parallel. I looked at mine and find that the axle is pitched at a greater angle than the transfercase. The axle shimms are attached to the springs so I don't think I can remove them for smaller ones. they are about 9/16's' tall at the front. should I drop the trasnfercase a bit more with a spacer, or get rid of the shackles? anyother thoughts without the SYE, to much cash for this old jeep.

~Art

[LVRockCrawler]

maybe a dumb question but what kind of vibes - could it be tire balance? my old 91 w/the 4" pro-comp lift didnt like the supplied angle shims so i changed them out - and if they are "attached" they can always be "unattached!" - probably the shims.... since the 1" shackles will increase the angle... and hey... you can always break out the grinder!!!! hope it helps!

[Ragtopman]

Vibration feels like its in the whole jeep like right under the floor. I also noticed my rearend is wandering a bit. I loosened it up twice now and lined it back up. I seems to be moving slightly off center to the left. In short the left tire sticks out from the frame about 1/2" or so more than the right. I cut off the rear track bar to get it off was that wrong

[LVRockCrawler]

i've omitted the rear trac bar on both the 91 and the 89 i have now... you'll find thats pretty common mod with leaf lifts... where is the axle drifting at - the spring perches? (they should be pinned with the springs) or are the shackles angling over? - the springs should be rigid enuff front/rear to keep the axle in line...

[Bounty__Hunter]

It's likely the shackles are throwing the pinion angle off, the shims on the lift springs were likely designed to be used with stock shackles. You'll have to remove the lift shackles or install new shims to correct the pinion angle.

You can change out shims by removing the center pin in the leaf pack.

[Ragtopman]

I know this is old but I wanted to add it incase anyone else had the problem. Bounty you are correct. I grabbed a set of stock shackles off a wreck slapped them on, no vibration anymore. Feels like a new jeep. Or at least the way it felt before the lift thanks

[TwistedCopper]

I am sorry I didn't suggest you loosen the bolts under the transfer case that hold the tranny to it, drive it gently around the block, and then retighten them (before you removed the shackles). This should be done whenever you lift a YJ, it allows the transfer case to re-position itself after the lift.

As for centering the rear axle, is it centered now? It's likely that if you used a trackbar bracket back there the added lift of the shackles were throwing the rear off center. I'd ditch the rear trackbar anyhow.

[Ragtopman]

Twisted, Did the transfer case bolts about 4 times didn't help. I also removed the track bar from the start. had to cut it off. The rear is over about a 1/4 can't really notice without a tape. I'm happy with it

[TwistedCopper]

Did they move at all?

[Ragtopman]

1/2" then drove around the block tighten them back up