lifted ZJ vibrates, someone help!! - JeepForum.com
 
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post #1 of 9 Old 11-15-2015, 11:56 AM Thread Starter
MDtags98
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lifted ZJ vibrates, someone help!!

Hey guys, this is my first post on here so bare with me. Two weeks ago I got a 3.5" Rough Country lift for my 98 Grand Cherokee. Install is all complete and now I have a vibration that I just cant figure out. It never did it before the lift, and it started as soon as I put it on. It starts dead nuts on 30mph, smooths out about 35, returns about 38 (at a higher pitch if you know what I mean), then smooths out at 45. I might feel it a little bit around 55 60 as well. Anything under 30 is totally smooth, and between 45 and 55 is too. If I let off the gas it goes away a little bit, but I think that's just because it slows down to a speed that it doesn't vibrate at. If I coast to a stop from 50mph, I still feel it at all the same speeds as when I accelerate. I replaced the u joints on the front and back of the rear drive shaft and nothing. I pulled the front drive shaft and test drove and still no change. I kinda ran out of ideas here so any suggestions will be much appreciated!

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post #2 of 9 Old 11-15-2015, 12:29 PM
OverlandZJ
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Rear pinion angle.. contributing to driveline vibe. Investing in adjustable length control arms can fix it, lots of info here on the forum can be brought up in a search.
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post #3 of 9 Old 11-15-2015, 12:44 PM Thread Starter
MDtags98
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thanks ill give it a try. is there any way to check that without buying the new control arms? I think you might be right though. the RC control arms with that kit are like an inch and a half longer than the stock ones. you are talking about the rear LCAs right? not the front
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post #4 of 9 Old 11-15-2015, 01:35 PM Thread Starter
MDtags98
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oh okay I see what youre talking about. the shorter control arms will turn the diff upwards to make it meet the ds more head on. correct?
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post #5 of 9 Old 11-15-2015, 03:45 PM
OverlandZJ
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Didn't realize you had aftermarket control arms. I have no experience with those fixed arms, I opted for adjustability.

Guess you need to see where it's sitting, get yourself something like this and get a measurement. Then you'll know which direction it needs to go.

http://www.amazon.com/Johnson-Level-.../dp/B00004T807

Another option I suppose would be a transfercase drop.. but those have the adjustment your looking for. Seriously, do a search and you'll most likely find well written threads showing pics and drawings that'd help you understand. As well as your options.
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post #6 of 9 Old 11-15-2015, 03:57 PM
kg6mov
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You should not need a t-case drop on a ZJ at that height.

The pinion yoke of the diff should parallel with the t-case output at ride height.

Your description also sound like it's at certain RPM ranges that it vibrates. Have you checked your motor and trans mounts as well as your harmonic balancer?


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post #7 of 9 Old 11-15-2015, 05:10 PM
green98ZJ
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I second that you don't need a t case drop. I had one on before I swapped transmissions and it vibrated at 45 mph. I decided to ditch it since I knew it was unnecessary once I had everything out. Now I don't have any vibes (knock on wood)

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post #8 of 9 Old 11-15-2015, 08:58 PM
t600
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Can you pull your rear DS and do a test run in front wheel drive? If it still vibrates I'd look at the mounts and balancer like Kg said.
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post #9 of 9 Old 11-16-2015, 05:59 AM
MurdaJs
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If you installed longer than stock rear lower cas and kept stock length rear upper cas, your pinion angle must be pretty bad. Either get longer uppers or shorter lowers, or adjustables.

Id pull the driveshaft, cover the tcase output if it is the internal slip yoke style, and go for a drive to see if the vibes go away.
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