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Discussion Starter #1
Just wondering for those that have shackles if you've experienced any
vibration specifically when accelerating from a stop. Can shackles cause
driveline vibration? I've got the AC shackles by the way.
From other posts, AAL seems to cause this but haven't read anywhere about
shackles causing this.

I can't say for certain but at times there seems to be one. It's not a strong one.. kind of faint.
That's why I'm not sure if it's the driveline. I'm thinking
it could also be from the tires or the aftermarket exhaust (Ultraflo).

Funny how after you do a mod, you can't remember how it was in stock
form.
 

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I've had shackles on my truck since they have been out and haven't had any vibrations. Maybe you got some tires that are out of balance. Also check to see if you have mud caked onto the rear driveshaft. That has known to cause vibrations as well.
 

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noticed it too...

I have experienced the same thing after doing my shackle mod as well. I also have shrock sliders, so the small weights came off to put them on.

A few weeks later I started noticing the vibration. Real slight, kinda like a humm rather than a shake...

I did notice one other thing - it is inversely proportional to the amount of gas in the tank. I know, I know - WTF right? A full tank of gas = no vibration. Empty tank = maximum vibration.

Anyone else? Any thoughts?
 

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Looks like you are getting some bad vibes from your avatar. It sounds like due to the weight of fuel changing the vibes it is probably rear axle pinion angle.
 

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I knew I wasn't losing my mind... After installing my Daystar lift, I've got a pretty annoying vibration shudder when applying the gas at lower RPM's/speeds. I checked my propeller shaft and it's pulled out of the transfer case quite a bit.

I'm working with a shop to have a new, longer, lighter weight (aluminum) propeller shaft made that will also replace the rear flange pinion yoke with a more standard U-bolt configuration. By getting the slip shaft back into the transfer case like it was stock(or better) and adding some more flexibility via the two U-joints, I'm hoping that the shudder will disappear.

I've checked everything over multiple times to be sure it was all tight and to Nissan torque specs. The one thing that keeps coming to the forefront of the possible causes is the propeller shaft. When I loaded the Xterra down this weekend with a few small refrigerators, the vibration disappeared.

I'll of course provide an update once I get this new shaft installed.

Terry
 

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At the rear of the transfer case is a conical shaped casing which holds the slip shaft (maybe 1.5" diameter) connected to the propeller shaft via a universal joint. This shaft's outer surface is smooth and the inside is hollow with grooves. When the rear axle is pushed farther from the truck frame, something has to give in this linkage. To accomodate this movement (also when the suspension cycles up and down) a slip shaft is used.

In my case, it is clear by looking at the grease/oil build up on the smooth outside surface of the slip shaft how far in it used to sit in the transfer case. Now (with the lift) it is around 3/4+" further out. My hypothesis on this issue is that having the slip shaft out further (less bearing support) and the additional angle on the U-joint, a rotational imbalance has been created. This idea seems to have some merit since some of us have reported the vibration/shudder disappearing when the vehicle is loaded down in the rear (bring the height of the vehicle closer to if not back to the factory height - most likely where the Ujoint and slip shaft were designed to operate ideally on a continuous basis)
 

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I completely understand what you're saying. However, I cannot picture in my head how it could be causing a rotational imbalance since the rotating components involved are all still cylindrical.
 

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I got an interesting question...

Those of you with this problem. Did you get the truck aligned after the install was complete?
 

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Has anyone tried degree shims on the rear axle?
 

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I've had my truck aligned two times. It is now completely within spec. The caster is definitely at the high end due to the TC UCA's but still within spec.
 

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My shop says they fixed the vibration. They would not tell me what they did but it did not require a new propeller shaft, nor spacer. Must be something really "groundbreaking" cuz he said he didn't want the fix spread all over the internet (whatever that's about...)

Guess we'll see when I pick it up. Of course if it's some half-baked/unreliable remedy, I'll definitely be pursuing alternative avenues.
 

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Discussion Starter #16
HOpefully it's a cheap and easy fix... assuming the shop will tell you what
was done. My vibration is still there but it's been so long, I pretty much
have gotten used to it b/c it's not constant and is not really strong. Tho
every now and then it shakes a bit stronger.

speedy_parker said:
I did notice one other thing - it is inversely proportional to the amount of gas in the tank. I know, I know - WTF right? A full tank of gas = no vibration. Empty tank = maximum vibration.
I've got to test out your theory. :bounce: I never have more than half
a tank of gas at most at any time. With the price of gas, a fill up and I'm
broke. Better to spread out the gas money. :cheers:
 

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2006x,
You need to, diplomatically, insist that he reveils the miracle fix.
 

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2006x said:
My shop says they fixed the vibration. They would not tell me what they did but it did not require a new propeller shaft, nor spacer. Must be something really "groundbreaking" cuz he said he didn't want the fix spread all over the internet (whatever that's about...)

Guess we'll see when I pick it up. Of course if it's some half-baked/unreliable remedy, I'll definitely be pursuing alternative avenues.
When i used to manage a bicycle shop would had these secret remedies... it's called BFH... big freakin' hammer, in case you don't know!
 

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well, it's not completely fixed but quite a bit better...

they checked over everything but finally determined that with the soft leaf springs, the pinion angle in the rear diff changes just enough under certain loads to exceed the ideal conditions for the funky CV joint Nissan put at the rear end of the propeller shaft. with that said, the partial fix involved improving the functionality of the CV joint itself. the job was done while I was at work so I can't really provide any solid details other than the vibration is now only occasional and significantly reduced.

the next step is to machine a spacer out of T6-6160 aluminum(I think that's what he mentioned) to fit in between the companion flange and the propeller shaft. after further discussion, I believe that this will help reduce some of the angle on the joint(s) and will definitely push the slip shaft back into the transfer case where it should be

The expense wasn't that bad but was comprised mostly of R&D (trying to fitgure out where the weakest link was and how to tackle the odd setup).

Unfortunately, the idea of changing the propeller shaft completely was scrapped because the pinion yoke on my 06 OR model has a spline count and some other dimensions that do not match any existing ubolt yoke's on the market that we were thinking of replacing mine with. If this was possible, it would have allowed us to have U-joints on both ends of the propeller shaft (hopefully elimating the vibration) and with the lengthened new shaft, could have pushed the slip shaft back into the transfer case the proper distance.
 

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