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post #1 of 12 Old 02-14-2013, 02:13 PM Thread Starter
sxysouthtx
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Acceleration Shimmy

Ok, I've searched, searched again, and searched some more. But I haven't found anyone that has had this problem who has solved the issue.

I only have a vibration when accelerating from a dead stop. The harder the throttle, the more vibration. I can feel the whole jeep vibrate in the seat of my pants. When I accelerate downhill, there is no vibration. There isn't any vibration while cruising at any speed or accelerating while already traveling at a decent speed. Only first gear vibes. Also, when accelerating from a dead stop going uphill, the vibes are greater.

I started to think this was maybe a 32RH problem. But no such problem have been posted that mirrors mine. So I'm leaning towards pinion angle. I'm not sure the exact angle I need. I think the axle is shifting downwards during acceleration, but I have no proof of this happening. I am really stumped here.

The rear u-joint is solid. I have tried to wiggle that little bastard with great force but it will not budge. So any help will be greatly appreciated. If one of you can help narrow this down, I will reward you with a magical fire breathing kitten that smites all enemies. That a huge reward.

Thank you.

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post #2 of 12 Old 02-14-2013, 02:38 PM
YJ4LIFE
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looks too high so with torque froma stop it will twist even higher

'89 YJ, 4.2L, ax-15, B&M shifter, 1" BL, TJ flares, '99 intake, '91 EFI, 5.0L explorer injectors, GenRight tank & stretch, 35" ProComp Xtreme muds, 52" chevy springs rear, 44044 Ranchos front.....
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post #3 of 12 Old 02-14-2013, 02:54 PM
jokerchief462
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With a slip yoke shaft your pinion angle should be level with the T-Case not pointed at it. Check these pics.
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2joint_angle.gif   cv_angle.gif  

89YJ 2.5L TBI, AX-5, NP231 SYE, Ford 8.8, Yukon Grizzly, Tom Woods Shaft, 33" BFG T/As, 4" lift, Warn VR10000s.

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post #4 of 12 Old 02-14-2013, 02:57 PM Thread Starter
sxysouthtx
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It looks like I need to point my diff downwards then. How would I go about doing that?

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post #5 of 12 Old 02-14-2013, 03:10 PM
Joe Dillard
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Check the motor mounts, tranny mount, and torque bushing.
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post #6 of 12 Old 02-14-2013, 03:11 PM
Day215
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Quote:
Originally Posted by sxysouthtx View Post
It looks like I need to point my diff downwards then. How would I go about doing that?
Have the vibes always been there, or is this a new issue? I have the same issue, my driveshaft and pinion are 10 degrees different from each other. My issue is caused by sagging springs, the full size spare and all the body armor made them sag. You can check the angle with an angle finder, then order some all steel shins in the degree that's needed. The other method would be welding the perches on at the correct angle.
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post #7 of 12 Old 02-14-2013, 03:21 PM Thread Starter
sxysouthtx
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Ah, thank you. The shimmy has been there since I can remember. I think the PO just threw some shims under there and called it good. Also, motor mounts, tranny mounts seem to be tip top. I'm not sure what a torque bushing is however. Thank you guys for all of your help. Hopefully I can get this resolved in the near future.

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post #8 of 12 Old 02-14-2013, 04:02 PM
skyj
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Quote:
Originally Posted by sxysouthtx View Post
Ah, thank you. The shimmy has been there since I can remember. I think the PO just threw some shims under there and called it good. Also, motor mounts, tranny mounts seem to be tip top. I'm not sure what a torque bushing is however. Thank you guys for all of your help. Hopefully I can get this resolved in the near future.
Remove the shims the po put and see how it does definately looks high and the torque bushing is only if you have a manual tranny.

build thread: http://www.jeepforum.com/forum/f22/skyj-eccentric-build-1467426/ '90 YJ 5.2 magnum MPI, AX15, NP231 SYE, Dana 30 4.56 open/ 8.8 4.56 detriot locker. 1" shackles
2" BL, 4" stretch all on saggy waggy springs.
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post #9 of 12 Old 02-14-2013, 06:21 PM Thread Starter
sxysouthtx
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Thank you. Am I right in saying that there should be a give or take 2 Degree difference for the angle? Hopefully this will work out.

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post #10 of 12 Old 02-14-2013, 10:19 PM
jokerchief462
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you don't really want a difference but you still have to take in account for axle wrap which means that when you step on the gas the spring flex and the pinion angle rises momentarily. There was a great video at youtube on axle wrap if you want to take a look. So the max would be 2 degrees.

89YJ 2.5L TBI, AX-5, NP231 SYE, Ford 8.8, Yukon Grizzly, Tom Woods Shaft, 33" BFG T/As, 4" lift, Warn VR10000s.

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post #11 of 12 Old 02-15-2013, 08:40 AM Thread Starter
sxysouthtx
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I understand axle wrap. I've seen guys with really built rigs having to use anti-wrap bars to prevent spring inversion. Luckily, I'm not going that route. I'm just concerned about the caster on the rear axle. It seems to be pointed too high. When I get an angle finder, I'm going to fix this pig. Thank you for the help.

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post #12 of 12 Old 02-15-2013, 08:58 AM
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Quote:
Originally Posted by sxysouthtx
I understand axle wrap. I've seen guys with really built rigs having to use anti-wrap bars to prevent spring inversion. Luckily, I'm not going that route. I'm just concerned about the caster on the rear axle. It seems to be pointed too high. When I get an angle finder, I'm going to fix this pig. Thank you for the help.
^ I think u mean ur pinion angle, but we get the point. It does look a tad high to me, bring it down a few degrees n u should b fine. On the axle wrap part, setting I lower to account for the pinion raising when u press the gas is more important in a spring over setup, not so much spring under. Getting ur yokes parallel should b ur goal.
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