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Unread 03-22-2013, 03:11 PM   #1
bhansen99xj
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Rear end vibration..help please!

So this has been a rough couple of weeks. I broke a leaf spring and ripped of my exhaust. A friend and I replaced the AAL + blocks 3" lift with some 3" rough country leaf packs. I took the XJ to a shop to have a new cat and muffler installed. Now, after everything has been repaired, I get some wicked vibrations at 55 - 70 mph. At 70 mph the vibes dull to a hum. It sounds and feels like it is coming from the rear as I don't feel it strongly in the steering wheel.

Anyone know what the problem could be? Engines are my thing. Suspensions, trannies, beatings..not so much. I searched a little but didn't come up with much in the way of definitive solutions. Also browsing mobile so please excuse not doing a thorough search.

Thanks for any help!
Cheers!

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Unread 03-22-2013, 04:04 PM   #2
cbenez1
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You changed the driveline angle by lifting the rear. I'm guessing you did not do a t-case drop or use angle shims to raise your pinion angle ? Either one of these would help. The more expensive and sure way would be a slip yoke eliminator. Use the search for any of these 3 and you'll get all the info you need.
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Unread 03-22-2013, 04:14 PM   #3
bhansen99xj
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The old lift was 3" and this problem didn't exist then. This is why I'm confused. Take out a 3" budget block/AAL and replace with 3" leaf packs. Thinking nothing should have changed.

The vibes really started when I snapped one of the original springs. Passenger side. I thought the vibes were related to the uneven angles I was traveling at.
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Unread 03-22-2013, 07:46 PM   #4
cbenez1
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Didn't realize it was lifted prior. However the lift blocks may have been taperd like a shim. Or you've got something wrong in the diff. Is it the same height with the new springs or did it change at all ?
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01 XJ 'Up Country' 3.5 on 29's former fire vehicle. Bright red. "Fire Wagon"
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Unread 03-23-2013, 01:51 AM   #5
VTEK1
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Is it possible that the "3 inches" of lift could have shagged and the new "3 inches of lift" is actually higher giving you just enough more lift to cause the vibes. My 3 inch lift actually helped my vibes but my XJ's leafs were inverted the day I bought it 5 years ago. Just my 2 cents.
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Unread 03-23-2013, 01:56 AM   #6
91AzXJ
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Try the simple things first and balance your rear tires. Also jack up the rear and put it on stands, then have someone slowly run it and watch to see if your drive shaft might be out of balance.
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Unread 03-23-2013, 03:10 PM   #7
bhansen99xj
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The block appears to have a slight taper to it. Does anyone know what the tolerable angles for the tc-driveshaft-differential should be? Really want to verify before I assume I need to drop the tc or go SYE. I don't want to put those efforts into it and find I need to change my axle bearings ot have to rebuild the differential.
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Unread 03-23-2013, 03:12 PM   #8
bhansen99xj
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I forgot to mention that I did rotate and balance all 4 tires and still have the same vibes starting at 55 mph.
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Unread 03-23-2013, 04:15 PM   #9
JeepN4KC
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Put some 4* shims to the leaf springs and go from there. Personally, I don't care for t-case drops but I've got a 1" spacer drop kit layin in the tool box I'd sell for cheap.
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Unread 03-23-2013, 04:29 PM   #10
cbenez1
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I agree with Jeepn4kc. 4 degree should do it.
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Unread 03-23-2013, 05:17 PM   #11
bhansen99xj
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Is that something that would involve removing the springs all the way? Just looking at degree of difficulty and how much time I have to dedicate (how much time I can get out of spending time with my outlaws lol)
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Unread 03-23-2013, 06:17 PM   #12
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Quote:
Originally Posted by bhansen99xj View Post
Is that something that would involve removing the springs all the way? Just looking at degree of difficulty and how much time I have to dedicate (how much time I can get out of spending time with my outlaws lol)
Jack the Jeep up and put stands under the unirails.

Wheels off.

Let the axle drop and set on another set of stands.

Unbolt the u-bolts.

Unbolt the center-pin of the leafs (some guys use c-clamps to hold the packs together)

Bolt the shim to the bottom of the packs with the center-pin.

Torque the u-bolts back down.

yada yada - pretty much a cliffnotes run through but you don't have to remove the leafs to install shims.
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Unread 03-24-2013, 03:30 AM   #13
sAe23
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Quote:
Originally Posted by bhansen99xj View Post
The block appears to have a slight taper to it. Does anyone know what the tolerable angles for the tc-driveshaft-differential should be? Really want to verify before I assume I need to drop the tc or go SYE. I don't want to put those efforts into it and find I need to change my axle bearings ot have to rebuild the differential.
If you don't have a SYE, the pinion and T-case output need to be parallel.
Get a cheap angle finder and MEASURE your setup before installing shims...
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Unread 03-24-2013, 05:42 AM   #14
JeepN4KC
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Quote:
Originally Posted by sAe23 View Post

If you don't have a SYE, the pinion and T-case output need to be parallel.
Get a cheap angle finder and MEASURE your setup before installing shims...
Good point. Hell I'm not an "app" savvy dude but I have an angle finder/level app on my phone.
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Unread 03-24-2013, 09:25 AM   #15
cbenez1
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Quote:
Originally Posted by sAe23 View Post
If you don't have a SYE, the pinion and T-case output need to be parallel.
Get a cheap angle finder and MEASURE your setup before installing shims...
In a perfect world maybe but thats a little overkill in most cases. Neither of my Xj's are parallel and both have no vibes. I would go with lessening the angle until the noise/vibration goes away.
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91 XJ 4.0 5spd 5.5 on 32's, flat flares, sand camo'd. "Battle Wagon"
01 XJ 'Up Country' 3.5 on 29's former fire vehicle. Bright red. "Fire Wagon"
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