Can I use adjustable rear control arms to adjust my driveline angles, and if so, how? - JeepForum.com
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Unread 05-22-2010, 11:25 PM   #1
guht
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Can I use adjustable rear control arms to adjust my driveline angles, and if so, how?

I am doing a UCF tummy tuck this weekend with a modified transmission mount that gives an inch more clearance. I already have a 1" BL and 1" MML, which also helps.

My driveline angle right now is around 11-12 degrees, and with this tummy tuck I am expecting it to reach at least 15, pushing me near the limit for vibrations.

My question is simply can rear upper and lower adjustable control arms help bring the driveline angles back down a couple degrees, and if they can how should I adjust them to do so?

Are there any GOOD writeups like 4x4xplor style detailing this topic?

Which end do I want towards the front, and which end do I want towards the rear in the picture below?



Thanks for looking!

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Unread 05-22-2010, 11:35 PM   #2
J03_TJ
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Adjust your lower arms to 15.75 and then adjust your uppers to get your pumpkin pointed at your transfer case. (You do have a SYE/Rubicon and new driveshaft right?) After that wheel it and see where your rear tires hit your flares. Here is mine set with 16" lowers.
moonrocks7.jpg  
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Unread 05-22-2010, 11:35 PM   #3
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Yes, they adjust you pinion angle. Bring the lowers to where you want the tire to sit in the wheel well. Then adjust the uppers to correct your pinion angle, it's that simple. Solid bushing goes to the frame and JJ goes to the axle. FYI for the front you can do this too, but keep your caster angle in mind. You have to find the "sweet spot" with the right pinion angle and the right caster angle. Good luck!
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Unread 05-22-2010, 11:41 PM   #4
guht
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Quote:
Originally Posted by J03_TJ View Post
Adjust your lower arms to 15.75 and then adjust your uppers to get your pumpkin pointed at your transfer case. (You do have a SYE/Rubicon and new driveshaft right?) After that wheel it and see where your rear tires hit your flares. Here is mine set with 16" lowers.
No lift, and NO SYE/CV yett.... That is coming next in a couple months... I was hoping I could still adjust the upper lower rears and effect the pinion angle in a beneficial way.....

Are you suggesting that this will not work without a SYE/CV.... If so why wont it work?

If not, then do I need to do something different then what you previously stated?

Thanks for the reply!
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Unread 05-22-2010, 11:42 PM   #5
guht
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Quote:
Originally Posted by SILASPRIT View Post
Yes, they adjust you pinion angle. Bring the lowers to where you want the tire to sit in the wheel well. Then adjust the uppers to correct your pinion angle, it's that simple. Solid bushing goes to the frame and JJ goes to the axle. FYI for the front you can do this too, but keep your caster angle in mind. You have to find the "sweet spot" with the right pinion angle and the right caster angle. Good luck!
Thanks!

I have front lowers, but no front uppers... Im going to leave front alone for now!
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Unread 05-23-2010, 04:08 AM   #6
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To my understanding, if you don't have a cv rear driveshaft then you want your rear angles to match. Meaning the t-case u-joint and the pinion u-joint should be the same. If they're not then you'll end up with vibes. When you put in a cv rear shaft then you want the pinion u-joint pointing straight at the t-case. Does that make sense? If I'm wrong on that someone will correct me.
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Unread 05-23-2010, 08:40 AM   #7
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After a certain amount of lift you can't get the angles correct with a stock setup. They need to be parallel and if you get it there your driveshaft angle will be too steep.
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Unread 05-23-2010, 10:09 AM   #8
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Quote:
Originally Posted by otisdog View Post
After a certain amount of lift you can't get the angles correct with a stock setup. They need to be parallel and if you get it there your driveshaft angle will be too steep.
jim
I really like the pictures, but I am confused. I wouldn't call adjustable control arms "stock", and I have read in many different threads that adjustable control arms are used to adjust pinion angle? Unfortunately this idea was not elaborated on, which is why I am asking for a proper and detailed explaination here. So what am I missing?

When using an angle finder what is the optimal angle of driveshaft, and please dont say 0, I am speaking realistically.

Also, when using an angle finder what are the typical tolerances between "NO VIBES" and "THAT ***** IS DEFINITELY GOING TO VIBE!!"

More pictures please!
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Unread 05-23-2010, 10:57 AM   #9
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Sorry - by stock setup I mean a stock two u-joint driveshaft. You can see in the pic that the t-case and diff angles need to be parallel. As you lift, and you are lifting by doing a belly-up, it gets hard if not impossible to retain thse angles - and if you do then the driveshaft angle can get too steep. I'm not sure what the maximum angle is but I guess you can try your project and see what happens. If you have vibes then you'll need the SYE/CV.
Jim

There comes a point where you just can't adjust the vibes away in the standard two joint short driveshaft on the Wranglers. That's why they SYE/CV system was developed. The SYE not only provides a fixed yoke on the t-case it also shortens the t-case to allow for a longer driveshaft and the CV works at greater angles. Below is what my driveline looked like after a 4" lift. I tried every way to deal with the bookoo vibes I had to no avail. I did an SY/CV right away.

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Unread 05-23-2010, 11:02 AM   #10
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If you don't have a SYE installed yet then you want to split the angle just like the first picture above.

The second picture shows a 0 degree angle at the axle end. Remember, this relationship is not the pinion to the ground. Its the angle between the pinion and the shaft, so in that second picture the axle side is zero. In my experience, with a SYE (cv drive shaft) I like to be 3 degrees or less. On a shaft with only two joints, you need to split the difference between the two (first picture).

Using just adjustable upper arms you can move your pinion up by lengthening them (typical) or down by shortening them (not typical).

Hope that helps.
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Unread 05-23-2010, 11:17 AM   #11
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Lower adjustable control arms set wheelbase. (front axle to rear axle measurement)

Upper adjustable control arms set pinion angle.

Another issue to consider, besides pinion angle, is the overall drive shaft length. The slip yoke can only travel so far before it's an issue. When one installs an SYE (slip yoke eliminator) and CV style driveshaft the slip yoke at the t-case will be moved to splines in the driveshaft (also longer than stock) that will make up this difference in length as the rear axle travels with suspension movement. In the pic above (stock shaft), you can see that the rubber boot is pulled open quite a bit.

For a stock shaft (2 u-joints), the u-joint angles need to be equal and opposite. In other words, the t-case output shaft and the pinion should be on the same plane.

For a CV style shaft (3 u-joints), the pinion angle should be +/- 1 degree relative to the driveshaft.

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