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Unread 06-22-2013, 08:48 AM   #1
jollyroger
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Front DL vibes: Need to know options

I have a 2001 XJ that I put a 4.5 in lift on about a year ago. It drives fairly well until I hit speeds around 60-65mph. At these speeds I have a front drive shaft vibration/harmonic noise. You can hear the shaft spin out of balance (sounds like it winds up) then wind down, repeat, repeat, repeat.... Rear has no issues even w/o a SYE.
Usually the jeep sees very little highway service - something to do with the 15mpg's - however; I have driven the Jeep to CO twice and will do so again this summer. My solution in the past has been to remove the front DS while I am on the interstate & reinstall once I arrive. As well as this works I want to set this Jeep up correctly because I really do like the XJ. What are my best options to make this Jeep do 75-80 mph and still drive like it did pre-lift? 2001 XJ has the low pinion D30. Is a hi-pinion D30 the *correct* and best way to fix this? If so, are there any certain years I would need to look for or avoid when looking for a replacement front end? Are there any less expensive and effective options I should consider first? The jeep was aligned post-lift and I would consider the caster to be maxed out in the sense that the Jeep does not seem to re-center the steering wheel after a turn as well as other vehicles I own, and have owned, very well already. So I would rather not tip the axle any further in the up direction.

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Unread 06-22-2013, 08:59 AM   #2
CJ7-Tim
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Long arm lift, short arms, drop brackets, whatcha got under there ? Are all your steering and suspension components in good or better condition ? Drive shaft u-joints and slip yoke good? Had it re-balanced ?

Pinion angle is more important than caster angle on a lifted XJ. Not recentering can be a sign a failing ball joints, or the need for more toe-in. If you had a retail tire store perform your alignment, they probably used specs for a stock Jeep.
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Unread 06-22-2013, 09:43 AM   #3
jollyroger
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The XJ currently has RC short arms, but planning to add long arms when time permits. Those short arms are ROUGH. Are you pleased with your long arms? I would consider the front end components to be in good condition. I could be mistaken, but I thought caster angle and pinion angle to be m/l the same, depending on which part of the axle you are measuring. IE tipping the axle will affect both, correct? I suppose (assume) I could probably adjust the pinion upwards to reduce the vibes since the front has a factory CV, but (I think) it would adversely affect the caster and therefore steering. This has been recommend (by Rough Country) as a possible solution because as you said the alignment shop probably has room to tip the pinion up some more. I would guess, based on my driving of the Jeep, the shop could not tip the pinion up enough to eliminate the vibes without a negative effect on the steering. I did not have the DS balance checked after the lift. Should I start there? I was kind of wondering/assuming this is a typical problem for low-pinion D30s with 4.5 inches of lift, but perhaps not. Thank you for your help.
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Unread 06-22-2013, 09:54 AM   #4
CJ7-Tim
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At 3.5" of lift and with short arms, I had no vibes and the steering was acceptable. When I installed control arm drop brackets and lifted to 5.5", I still have no vibes and have acceptable steering with stock parts. Short arms ride rougher the taller you lift, so at about 3-4" of lift you should consider drop brackets.

Pinion angle is more important than caster angle. As the pinion tips up to point at the transfer case, the caster angle decreases. Maintaining stock caster on a lifted Jeep with short arms is not going to happen.

Point the pinion directly at the transfer case and make sure your toe-in is 1/16 - "1/8". Use as much pinion angle as needed to reduce/eliminate vibes and also to maintain some caster.

Consider installing control arm drop brackets. A HP D30 may help with drive line angles.
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Unread 06-22-2013, 10:03 AM   #5
jollyroger
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Sounds good. I will try that first. I was suprised when I installed the lift it looked like the factory D30 pinion angle was nearly flat. I thought a CV needed to point up at the TC? I do have CA drops already.
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Unread 06-22-2013, 10:40 AM   #6
CJ7-Tim
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Edited for clarity : Point the pinion directly at the transfer case ...
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Unread 06-22-2013, 05:13 PM   #7
lazyxj
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Quote:
Originally Posted by CJ7-Tim View Post
Edited for clarity : Point the pinion directly at the transfer case ...
My 01 XJ had terrible front shaft vibs, especially after regearing to 4.56s.
After trying several wrong things, I aimed the D30's yoke directly at the driveshaft so the angle was less than a half a degree...vibs gone completely.
The FSM says pinion angle (less than 1 degree) supersedes caster specs.
Follow CJ7-Tim's suggestion and see how it feels
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Unread 06-22-2013, 09:48 PM   #8
Millermagic
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3.5'' of lift on my 2000 XJ and I had HORRIBLE vibes. Unfortunately, I thought it was coming from the rear ... Run it without the driveshaft whenever you can; otherwise, you'll kill the pinion bearing, pinion and ring gear :S
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Unread 06-24-2013, 07:03 AM   #9
jollyroger
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Thanks for the advice. Will try adjusting pinion angle first and go from there.
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