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Unread 08-30-2012, 11:29 AM   #1
straightsixjeep
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Bad Vibes :(

Hey guys, quick question for ya. 1 week ago I had brand new tires mounted and balanced on my 98 cherokee. It drove smooth as butter and all was well. I went ahead and replaced the leafs springs since the stock ones sagged. I replaced the leafs packs with heavy duty crown ones, new rugged ridge leaf shackles, and new u-bolts. Since Iv replaced those things I get a nasty vibration between 37-40mph. Once I accelerate to around 37mph it starts vibrating real bad, you can see the rear view mirror shaking but it goes away right after 40mph and its smooth again. Decelerating it does the same thing once I hit 40mph but its smooth again from 37mph (apx.) until Im stopped. I took it back to costco and had the tires re balanced, this made no difference with the vibration. Can it be the pinion angle even though the leafs arent lifted leafs? I took it to class and stuck it on the alignment rack. Everything was perfect however the rear axle thrust angle is slightly off. I jacked it up, loosened the u-bolt nuts and try to re-position the axle. This didnt change anything. So im thinking its either the thrust angle or a pinion angle issue. Any ideas? I want to fix this before the vibes take out the new u-joints I just put in. Thank you

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Unread 08-30-2012, 01:26 PM   #2
sAe23
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Are the new shackles the same length as the ones they replaced?
Are the new u-bolts in the same spot as the old ones?
Have you measured the angles of your transfer case and pinion?
Do you have any shims?
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Unread 08-30-2012, 02:16 PM   #3
straightsixjeep
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Quote:
Originally Posted by sAe23 View Post
Are the new shackles the same length as the ones they replaced?
Are the new u-bolts in the same spot as the old ones?
Have you measured the angles of your transfer case and pinion?
Do you have any shims?
The new shackles are the exact same size, Id imagine the u bolts are in the same spot as well since theres not a lot of room to move them. I dont have any shims and I do not have a pinion angle gauge. I guess my next step is to check the pinion angle. Could I really have a pinion angle issue after replacing leafs with new leafs of the same size?
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Unread 08-30-2012, 07:44 PM   #4
sAe23
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It's possible, if the old ones were saggy enough. And I presume you did one side at a time, so the axle probably could not move sideways...

It rode smoothly before the change, so unless you knocked a wheel weight off during the install, it's likely related to the new ride height.
But, maybe rotate the wheels anyway and see if anything changes??
Or if you have a SYE you could pull the driveshaft and shift to 4WH and drive a bit to see if it goes away.
(Don not try w/o a SYE)
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Unread 08-30-2012, 08:31 PM   #5
straightsixjeep
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Quote:
Originally Posted by sAe23 View Post
It's possible, if the old ones were saggy enough. And I presume you did one side at a time, so the axle probably could not move sideways...

It rode smoothly before the change, so unless you knocked a wheel weight off during the install, it's likely related to the new ride height.
But, maybe rotate the wheels anyway and see if anything changes??
Or if you have a SYE you could pull the driveshaft and shift to 4WH and drive a bit to see if it goes away.
(Don not try w/o a SYE)
At first I thought it was a wheel weight so I had the wheels re balanced and it still vibrates. Also, I did replace one leaf at a time. Thats why I dont understand why my thrust angle is off? Could that cause vibes?
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Unread 09-01-2012, 01:50 PM   #6
sAe23
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If the thrust angle is off enough (and I don't see how it could be on a leaf spring suspension) it could cause the u-joint to bind...
BTW, how much IS it off??

I'm guessing you do NOT have an SYE? I wonder if there is a way to drive w/o the rear shaft and NOT spill fluid?

Sure wish someone with more "forum cred" (like CJ7-Tim) would chime in (hint hint)
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Unread 09-01-2012, 02:09 PM   #7
straightsixjeep
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Thanks for the reply. I will go try to find my alignment sheet to check the thrust angle. No sye, the xj is completely stock. I am able to remove the rear driveshaft without fluid coming out however I dont want to take it up to 40mph in 4wd (fwd) to check for vibration. I need to get an angle finder to check the pinion angle. It wasnt lifted enough to cause any issues, this is what I dont get. Hopefully cj7-tim sees this, he has given good information before.
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Unread 09-01-2012, 02:15 PM   #8
sAe23
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I've driven 65+ (I have an SYE) w/o problems... Just don't punch it off the line
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Unread 09-01-2012, 02:38 PM   #9
straightsixjeep
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So pull the rear driveshaft, put it in 4hi, and take it up to vibration speeds?
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Unread 09-01-2012, 03:27 PM   #10
straightsixjeep
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Total toe for the rear is .40*, the rear thrust angle is -.24*. The right rear toe is .44* and the left rear toe is -.04 degrees ??
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Unread 09-01-2012, 06:22 PM   #11
Millermagic
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If he has a 98, he can pull the rear shaft without spilling fluid.
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Unread 09-01-2012, 07:29 PM   #12
straightsixjeep
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Are those numbers way out of wack? Tires are 1 week old I really, REALLY dont want to tear them up from something out of alignment.
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Unread 09-01-2012, 09:17 PM   #13
BUSA
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Quote:
Originally Posted by straightsixjeep View Post
Total toe for the rear is .40*, the rear thrust angle is -.24*. The right rear toe is .44* and the left rear toe is -.04 degrees ??
Is that what the alignment suppose to be on the XJ's
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Unread 09-01-2012, 09:57 PM   #14
straightsixjeep
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Quote:
Originally Posted by BUSA View Post
Is that what the alignment suppose to be on the XJ's
Im not sure I just posted my jeeps specs, hoping to hear from someone more experienced if these numbers are an issue. My alignment sheet does not show the specified range for the rear toe or thrust angle. I replaced my leaf springs but I am getting bad vibrations so I want to find out why before it takes out my new u-joints. Also, Im wondering if my alignment numbers are bad because I really dont want my week old tires to wear quickly due to something out of alignment. Overall the specs for the front end are pretty good, however the rear thrust angle is to far off (I read the specified range is -.15* to .15*) and also the rear toe seems odd. The driver side rear to is -.03 where the passenger side rear toe is .45. I loosened up the u-bolts and tried adjusting the rear axle however it didnt move much, probably because the centering pins lock it in place which makes me wonder how these #'s are off. I am the 2nd owner, it has a clean carfax and shows absolutely no evidence of it being in a collision. I just want to get in and drive my jeep with no worries, Im battling several issues right now and dont even want to drive it. Its driving me nuts
Edit: just took a measurement of the wheelbase. The driver side rear wheel center to the driver side front wheel center is 101.5in, exact same for the passenger side. This is somewhat of a relief. I still dont have an angle finder however If I seriously have to correct the pinion angle just due to a possible 1in lift in the rear, instead of shims or a t-case drop im thinking about adjustable lower control arms. What do you guys think?
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Unread 09-02-2012, 08:29 AM   #15
Millermagic
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Should there be toe in the rear? It's a solid axle that doesn't turn ...
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