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Unread 03-10-2014, 06:06 AM   #1
smcurry83
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Driveline vibrations and control arm adjustment questions

What I have: 09 JKU auto, 4" Teraflex w/ front upper & lower and rear upper adjustable control arms, 35's, and a JE Reel front ds.

Bought it used in December as is (minus the snow pile).



I know the issues with lifting a jeep. I previously owned a 00 TJ with a 4" short arm and 35's.



Right now my JK drives great. I can easily cruise @ 75 with a single finger on the wheel all day long.

I do have some drive line vibes that I want to address if possible. I'm thinking about adjusting the control arms to find the best balance between pinion angle and caster. Right now it drives so well, I feel there's some room to improve the pinion angle before it starts exhibiting bad steering tendencies.

My question is: How much can I adjust the control arms before I need to start adjusting other suspension and steering components? Can I make minor adjustments to the control arms without touching anything else without causing issues?

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Unread 03-10-2014, 07:56 AM   #2
smcurry83
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Quick update: I just pulled the front drive shaft so I can hopefully pinpoint if the majority of the vibrations are coming from the front or rear. I would assume if the vibrations haven't subsided at all, it's a rear drive shaft issue and if all/most of the vibrations are gone, it's a front drive shaft issue.
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Unread 03-10-2014, 09:23 AM   #3
RockyClymer
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With that much lift and a stock front axle - the best you can hope for is a tradeoff between caster angle and pinion angle. The good news is that the front is a high pinion so pinion angle is not near as critical as in the rear. I set my caster at about 4+ degrees and let the pinion be where it is at since there is no load on it 99 percent of the time. I did reset the rear pinion angle as if it were a double cardan setup, the stock rear shaft has lasted over 50 k miles now with no problem and no vibration.
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Unread 03-10-2014, 01:00 PM   #4
smcurry83
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So I'm guessing if the majority of the vibrations went away after removing the front driveshaft (JE REEL 1310), the vibrations I'm getting may be due to worn u-joints?

It's night and day difference without the front ds.



Still curious about this: How much can I adjust the control arms before I need to start adjusting other suspension and steering components? Can I make minor adjustments to the control arms without touching anything else without causing issues?
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Unread 03-10-2014, 02:59 PM   #5
SubAtomicGenius
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Perhaps the driveshaft is out of balance as well.
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Unread 03-10-2014, 05:06 PM   #6
RedRubiconLJ
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Could be tires and or tire balance as well. What happened when you pulled the front ds?
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Unread 03-10-2014, 06:38 PM   #7
smcurry83
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Quote:
Originally Posted by RedRubiconLJ View Post
Could be tires and or tire balance as well. What happened when you pulled the front ds?
Night and day difference. There is only a slightly noticable vibration now, probably from the rear ds. With the front ds installed, it vibrates bad enough that it seems like something is about to come apart.
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Unread 03-10-2014, 07:55 PM   #8
SoK66
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Ok, coupla things. The front control arm length specs that come with Teraflex's Flexarms are off by about 1" give or take a smidge. For whatever reason they just simply refuse to correct them, and making it worse, the specs in the kit instructions are different than the ones that come with the Flexarms. Cutting to the chase, use Synergy Suspensions' specs from their 4.5" kit and youll likely be spot on the money.

If the rig has Teraflex's driveshafts (Tattons actually) and matching yokes, check them carefully to ensure they were cut on center. A guy on here chased DL vibes for weeks and finally pinned it down to his front yoke not being on center. I checked my rear where I've had the issue and sure enough, not on center, and and my front one is off as well. Terrible issue given the cost.
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Unread 03-11-2014, 08:44 PM   #9
smcurry83
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So I still need to measure and see exactly how much lift I have and then address the pinion/caster angle.

In the mean time, I think I've found the cause of the vibration or at least a partial cause. The main joint in the double cardan is worn. There is no rubber boot on it at all.
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Unread 03-11-2014, 10:03 PM   #10
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Quote:
Originally Posted by smcurry83 View Post
So I still need to measure and see exactly how much lift I have and then address the pinion/caster angle.

In the mean time, I think I've found the cause of the vibration or at least a partial cause. The main joint in the double cardan is worn. There is no rubber boot on it at all.
I would worry less about your angles and more about where your castor is at. The pinion is along for the ride if you get your castor in spec.
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is it a plink plink kerrrrdunk? or more of a brrrrrconk doc doc miiiidge pang!!!? or is it a badonk ka donk? if it is the latter its just the normal fat *** of the JK

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Unread 03-12-2014, 12:34 AM   #11
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Yup, ideally, the axle assembly should be built to allow for both correct caster and correct driveline angles. With a 4.5" lift, you're simply gonna have to compromise for proper caster and sacrifice your pinion angle - just like any suspension/drivetrain when using big lifts with stock housings.
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Unread 03-13-2014, 09:19 AM   #12
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Quote:
Originally Posted by SubAtomicGenius View Post
Yup, ideally, the axle assembly should be built to allow for both correct caster and correct driveline angles. With a 4.5" lift, you're simply gonna have to compromise for proper caster and sacrifice your pinion angle - just like any suspension/drivetrain when using big lifts with stock housings.
No, no, no. #1 priority is the pinion angle. On a JK you just have to live with low caster. Allowing front driveline misalignment to continue on a JK is a prescription for the transfer case to explode. The OP has a lot of lift to be running a stock, uncorrected housing. Needs to get the pinion angle to within 1-2 degrees or so and just let the caster settle wherever it does. We've seen some JKs happy as a clam with 2.5-3 degrees caster after aligning the vibrations out of the pinion.
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Unread 03-13-2014, 09:51 AM   #13
smcurry83
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So I measured the at the front springs yesterday and I'm right at 4".

I'm in the middle of rebuilding my double cardan drive shaft right now (big pita).

Once I get that back together I'm going to figure out the pinion angle stuff.

I'm still curious: when I make adjustments to the control arms to change the pinion angle, will I also need to adjust the track bar and get an alignment done?
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Unread 03-13-2014, 10:31 AM   #14
smcurry83
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Quote:
Originally Posted by SoK66 View Post
The OP has a lot of lift to be running a stock, uncorrected housing. Neeloods to get the pinion angle to within 1-2 degrees or so and just let the caster settle wherever it does. We've seen some JKs happy as a clam with 2.5-3 degrees caster after aligning the vibrations out of the pinion.
When you say a pinion angle of 1-2 degrees, you mean a 1-2 degree difference between the pinion and driveshaft?
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Unread 03-13-2014, 06:15 PM   #15
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Quote:
Originally Posted by smcurry83
When you say a pinion angle of 1-2 degrees, you mean a 1-2 degree difference between the pinion and driveshaft?
Yes, sorry that wasn't clear.
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