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Unread 06-03-2013, 01:10 PM   #1
ZJMatt
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Driveshaft vibrations - angle or VC?

Jeep in question is the bottom one in my sig. Has an NP249 t-case. I know the viscous coupler is bad, I'll be replacing it once I get the money for a 242.

The previous owner installed a 4.5" lift but admitted to me that it was his first time lifting a vehicle. The only thing I've noticed that isn't ideal, is that he has front upper fixed arms. The front lowers are adjustable, as well as all 4 in the rear.

The jeep had never been off-road before I bought it. When I bought it, it didn't have the front driveshaft installed because he said it was giving him horrible vibrations since doing the lift, so he pulled it out. He also installed a t-case drop hoping it would fix the problem but he said it didn't. It was the CV style, which doesn't have the telescoping capabilities of the U-Joint style. So I swapped the pinion yoke and driveshaft out of my old jeep. I also took the t-case drop out, because well, it's a t-case drop.

I still have sporadic driveshaft vibrations. Sometimes it'll go down the road perfectly smooth. Other times it's just a light hum. Other times it'll shake everything. It's not even dependent on the speed - just whenever it feels like vibrating it will.

I measured the driveshaft angle with a digital inclinometer. It measures 11.6. I know the drive shaft and u-joints are good, since this shaft came out of my old jeep, which last time I drove it was 30 miles in front-wheel-drive, and it didn't vibrate or make any noise.

Also as I said I know the viscous coupler is beyond shot. I never did the figure-8 test because I could feel it just pulling out of my driveway.

So, could the viscous also cause a vibration? What should my driveshaft angle ideally be at? My guess is the p/o put in adjustable arms, but didn't know how to adjust them. To decrease the angle, I would want to adjust them in, correct?

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Unread 06-03-2013, 01:33 PM   #2
WhiteOut
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The pinion should be pointing at the output on the transfer case. Also possible you have a joint on its way out.

Pull the shaft again (your case is already wrecked) and see if the vibes continue.
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Unread 06-03-2013, 01:42 PM   #3
ZJMatt
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Quote:
Originally Posted by WhiteOut View Post
The pinion should be pointing at the output on the transfer case. Also possible you have a joint on its way out.

Pull the shaft again (your case is already wrecked) and see if the vibes continue.
As I said, the u-joints are OK. They were recently replaced when the shaft was in my other jeep, and I had no issues with that one.

What do you mean by "pointing at?" The driveshaft should have zero angle to it?

I don't want to pull the shaft because I frequently need 4 wheel drive.
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Unread 06-03-2013, 01:55 PM   #4
kg6mov
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Pinion bearing? Maybe missed something when you did the swap?

VC shouldn't cause vibrations, shot vc just means you are locked 4wd, which if anything would make any vibrations consistent with speed.

Pinion angle should be set so the driveshaft is basically straight coming out of the diff, and only bends at the t-case.
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Unread 06-03-2013, 03:12 PM   #5
WhiteOut
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Pull the shaft, drive around for 20 minutes and see if it happens.

Easiest way to eliminate a part.
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Unread 06-03-2013, 03:14 PM   #6
ZJMatt
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Quote:
Originally Posted by WhiteOut View Post
Pull the shaft, drive around for 20 minutes and see if it happens.

Easiest way to eliminate a part.
As mentioned, it does not vibrate with the front shaft removed. This front shaft also did not cause any issues in my old jeep (same lift height, longer fixed lowers & stock uppers). Therefore I don't believe it's the shaft itself or a joint that's bad, but instead my angles.

Here is a pic of the pinion yoke & shaft

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Unread 06-03-2013, 03:19 PM   #7
ZJMatt
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Just took a few more measurements, pinion angle as relative to driveshaft angle.

Pinion angle (inclinonmeter on the top of the u-joint yoke) - 1.0 tilted up
Driveshaft angle - 11.6 same direction.

So it seems the driveshaft is 10.6 off from the pinion, and they should be the same, correct?

Can I make this adjustment with fixed uppers and adjustable lowers?
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Unread 06-03-2013, 03:29 PM   #8
HighLonesome
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The cause of your vibes from looking at the pic. Pinion seal is leaking too, ergo I would check for lateral slop where the driveshaft enters the diff. You should have about 1 degree pinion angle.
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Unread 06-03-2013, 03:38 PM   #9
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Quote:
Originally Posted by HighLonesome View Post
The cause of your vibes from looking at the pic. Pinion seal is leaking too, ergo I would check for lateral slop where the driveshaft enters the diff. You should have about 1 degree pinion angle.
Unless I'm misreading that then I completely disagree. Pinion angle should be as close to the driveshaft angle as possible. The really crappy angle he has in the pics probably caused the pinion seal leak because the joint is out of alignment on the elliptical rotation with the CV joint at the case.

This is what it should look like

Iirc my pinion is around 5-7 degrees
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Unread 06-03-2013, 03:39 PM   #10
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Lengthen the uppers or shorten the lowers. To fix......
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Unread 06-03-2013, 03:42 PM   #11
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Diff should be pointing at the t-case output.
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Unread 06-03-2013, 03:50 PM   #12
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Quote:
Originally Posted by speedbucket View Post
Unless I'm misreading that then I completely disagree. Pinion angle should be as close to the driveshaft angle as possible. The really crappy angle he has in the pics probably caused the pinion seal leak because the joint is out of alignment on the elliptical rotation with the CV joint at the case.

This is what it should look like

Iirc my pinion is around 5-7 degrees
See how the driveshaft is a perfectly straight line coming from the diff? That is where the 1 degree should be.
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Unread 06-03-2013, 04:03 PM   #13
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Quote:
Originally Posted by HighLonesome View Post
See how the driveshaft is a perfectly straight line coming from the diff? That is where the 1 degree should be.
Angles are always given from 0(flat) or vertical from 90. I understand what you meant now
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Unread 06-03-2013, 04:25 PM   #14
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Originally Posted by speedbucket View Post
Angles are always given from 0(flat) or vertical from 90. I understand what you meant now
And you I.
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Unread 06-03-2013, 05:02 PM   #15
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FWIW, The LCAs are for axle placement in the wheel well and the UCAs are for pinion adjustment. To do it correctly, you need adjustable uppers to push the top forward until the pinion is the same angle as the DS.
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