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Unread 08-10-2011, 03:16 PM   #1
KyBoy1991
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1998 ZJ 
 
Join Date: Apr 2008
Location: Louisville, Kentucky
Posts: 672
Vibrations & Confused about Castor vs Pinion Angle

OK...so as many have probably seen my previous post, I have front drive line vibrations. I have adjusted and adjusted for the last 6 months, and have NEVER killed this vibration.

New 33x12.50 BFG AT's and an alignment now, and the shop tells me that I have to roll my pinion DOWN to get my castor back to proper specs/safe driving.

Well, if I roll my pinion down it will make that angle worse and my thoughts says make the front vibes worse.

So, I KNOW there are those of you that have GC's that drive properly and don't have vibes...so where is a happy medium?

I wander on the road when hitting a bump now, not horrible, but not great either. But I vibrate bad enuf to cause leaks that i didn't have when i raised the pinion to make the angle less and vibes less.

I have a great jeep, but can't figure this ***** out for the life of me!!! Have put calls in to KevinsOffroad & Carolina Driveline whom i purchased the shafts thru.

But I'm desperately looking for answers so right now, there isn't a stupid suggestion...i'll take advice for anything to help my issue.

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Unread 08-10-2011, 03:27 PM   #2
ajmorell
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Join Date: Jan 2006
Location: Santa Fe, New Mexico
Posts: 7,144
Good caster and a good pinion angle are somewhat mutually exclusive on a lifted Jeep. In order to stay within spec for the caster you're pinion angle is going to be way off. There is a happy medium. I'm at about the same amount of lift as you and have acceptable handling characteristics with no vibes at all. I think my caster is around 4-4.5* or so. There was a good diagram showing the proper way to set up the pinion angles somewhere around here that I saw recently. Basically for the front you want the pinion to be pointing nearly right at the output on the t-case.
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Unread 08-10-2011, 04:02 PM   #3
KyBoy1991
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1998 ZJ 
 
Join Date: Apr 2008
Location: Louisville, Kentucky
Posts: 672
Yeah, I have used that setup process. My problem, me thinks, is I have the D30 Low Pinion...which causes the angle to be more harsh....however, I just got it back from alignment and 0-40mph is perfect for me. And it's at 2* castor....they told me to get to 4* and hopefully that wouldn't effect the vibes. I may adjust and see, but right now if it doesn't do more than it did, I'm happy and will live with it!

But anyone else has advice, i'm all ears. My luck hasn't been great of late and don't see it working here, but keeping the fingers crossed. Chime in with any help please.
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Unread 08-10-2011, 04:16 PM   #4
ajmorell
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I was fine when I had the lp30 though too. Get it to around 4* and you should be good.
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Unread 08-10-2011, 07:26 PM   #5
melk
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1996 ZJ 
 
Join Date: Sep 2009
Location: Charlotte, NC
Posts: 2,891
The real problem is the BFG AT's.....
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Unread 08-11-2011, 02:15 PM   #6
KyBoy1991
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1998 ZJ 
 
Join Date: Apr 2008
Location: Louisville, Kentucky
Posts: 672
Ahhh come on now....the BFG TA KO's are proven tires now for years.....
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