post #1 of Old 07-25-2013, 03:12 PM Thread Starter
LightningFAST
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Pinion angle calculations - the math...

I'll make this as short and sweet as possible with all the info.

Bought a XJ back in February, love it, it had RC 4.5" lift with 33's. Took it and added 1.75" coil spacers/shackles. (Wouldn't clear the 33's on 4.5")

First time I stuffed it in the woods the RC leafs crapped out. Sagged on right rear side.

Bought Rusty's 4.5" leafs - they have 6 leafs compared to RC's 5. Sag is gone...RC leafs did have pinion angle shims under them - they were aluminum. They snapped when I took them off the RC leafs to try to put under the Rusty's.

From what I can see the Jeep does not have a SYE kit, it has a TC drop.

TC drop bushings measure 1-3/8"
Total suspension lift sits at ~6.25" suspension

Jeep is all back together and I really don't drive it unless I either want to be out in the woods or take it around town. I never usually go more than 55MPH, barely ever ends up on the freeway.

<55 I experience almost no vibration, if anything I think it comes from the tires. From what I vaguely remember, on the freeway I feel a little vibe around the 60MPH mark?

I don't want any issues so if I need shims I want them installed and I don't want to play a guessing game with what degree shims I'll need. I was told to put the shims that were under the RC leafs back under the Rusty's leafs here on the forum, but as I said they broke and I'm not sure if the difference in leafs makes them useless anyway...

I followed the directions in this article and got the following measurements:

http://4xshaft.com/tech_slopesVSangles.asp

Driveshaft: 22*
Not on the flat part of the yoke, the driveshaft itself right before the rear CV shafts/yoke

Rear diff: 6*

Transfer case drain bolt: 7*

What I do from here is unclear in the article...I'm not sure if I add them up and divide by 3 for an average of ~12* shims...? Seems high...

22-6-7 = 9/3 = 3* shim?

Math was never my strong point and the article is a little vague...

Sorry this ended up long anyway...help is appreciated.


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post #2 of Old 07-25-2013, 05:22 PM
CJ7-Tim
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At 3-4" of lift or more you should have already installed, or be saving for, a Slip Yoke Eliminator (SYE) kit.

Only buy and use steel shims. 2-4* shims may help with vibes on a T-Case drop. An SYE would probably need 4-6* shims.

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post #3 of Old 07-25-2013, 05:39 PM Thread Starter
LightningFAST
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I appreciate the response. I agree with you, I would feel much more comfortable if the jeep had a SYE kit. Unfortunately with being let go from my job, there's no chance a SYE will happen until I can financially bounce back. My Jeep is not a daily driver so I'm not worried about it. It will see minimal use.

Prior to replacing the RC leafs I had taken the Jeep on the freeway (~75-80MPH) and had no driveline vibrations.

Since replacing the RC leafs with the Rusty's leafs I have NOT been on the freeway. I have virtually no driveline vibrations now at <55. As I said, they may be very slight at the ~60-65MPH range...I guess I should take it out and test it and see.

If I am seeing zero driveline vibrations I'm not sure if I should shim the rear axle at all. That's why I'd like clarification on how the math is done, whether I need to apply it to the Jeep or not.

I'll check YouTube...don't know why I didn't think of that sooner.

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post #4 of Old 07-25-2013, 05:49 PM
CJ7-Tim
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If you don't have vibes, you don't need shims.

Here is pic of one our local club members who didn't think he needed an SYE:

.
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post #5 of Old 07-25-2013, 06:02 PM Thread Starter
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I'm not disagreeing with you - I would like a SYE; and will get one... it just won't happen until I can secure another job. As I said, the Jeep is barely driven, so it will happen...just not next week.

I'm going to take the Jeep on the freeway and see if I experience any vibrations.

For reference, here are some pictures I took earlier today. The housing looks uniform with the rest of the transfer case so that's why I suspect there is not a SYE, plus there is the TC drop. In my opinion the pictures do not capture the "severity" of the angle at both ends of the driveshaft, but I know I am a worry wart...

Also, MOST of it's mud...not rust.



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post #6 of Old 07-26-2013, 01:32 PM
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Pinion is to high, you want the yoke on the t case to be parallel to the yoke on the axle.

http://www.4xshaft.com/driveline101.html

98 XJ lifted/Locked/Geared
My Build: http://www.jeepforum.com/forum/f177/my-98-build-1253511/
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post #7 of Old 07-26-2013, 03:49 PM Thread Starter
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I'm aware of the fact that I can stand to adjust my pinion angle. All I was looking for was for someone to tell me HOW to do the math...

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post #8 of Old 07-26-2013, 04:12 PM
whitexj98
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You're over complicating it, put the angle finder on the tcase yoke to find what degree its at, do the same for the diff yoke, subtract the two and thats the degree shim you need.

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post #9 of Old 07-26-2013, 04:16 PM Thread Starter
LightningFAST
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Thank you...sometimes I need things explained to me like I'm 5 years old...

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post #10 of Old 07-26-2013, 04:20 PM
whitexj98
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Note: if you go to a sye kit thats all out the window, then you would want the diff yoke pointed straight at the t case yoke.

98 XJ lifted/Locked/Geared
My Build: http://www.jeepforum.com/forum/f177/my-98-build-1253511/
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post #11 of Old 07-26-2013, 04:22 PM Thread Starter
LightningFAST
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Yeah I do know if I go SYE it will all change. I do have every intention of going SYE when I can find another job. In the meantime I will buy shims anyway. They're cheap...

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