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Discussion Starter #1 (Edited)
Hey guys, So I've tried googling and not come up with much regarding the transfer cases. That said, truck used to be lifted, angles were bad, I pulled the lift, got the angles right and had some still, turned out the 2 Piece was out of round, opted and installed last week a new 1 piece drive shaft, my driveline angles are dead on, 2.4 degrees transfer case then driveshaft is 1.4, diff 2.2. I noticed right away a good bit of vibration gone but something still lingers!.

It used to be damn near constant, no longer is it. when I hit 70-80Km/hr It's like a harmonic hum type of vibration, as I speed up from 70-80 it increases, it's like the sound tires make as the road noise/harmonics come in then go away as you speed up.


I noticed it was like a "rolling" vibration, at highway speed with cruise on and flat ground it came and went constantly, When I let off it was there slightly, When I touched throttle lightly to not propel but its also not coasting, It was the worst, As I laid into the throttle it seemed to get smoother.

The transfer case output shaft I can wiggle up and down a bit but not excessively, I'd assume it should be held fairly snug otherwise that could "whip" around in there? truck has over 400k km on it so I'm sure the bushings had a ton abuse.... I did drain the oil out of it and there was fine shavings on the drain plug for sure, no big chunks, I'd estimate the drain interval was about 30k km before I did that recently., so I'd say probably abnormally high metallics.

had the rear diff locker mechanism break so I had replaced it out of it probably ~40k km ago, I'm a certified mechanic and had replaced that setup in there, there is no whine and bearings were new, so knock on wood there.


Does the front driveshaft rotate while driving in 2wd? I know my U joints on it are bad, In the drive way It free spins, I moved the truck ahead a foot and the drive shaft never spun... I was thinking if it somewhat started to spin down the highway it could cause a vibration I'm sure?.
 

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The front driveshaft shouldn't rotate much, if at all, as the gear driving the chain in the TC is free to spin in 2wd mode, and the front differential is unlocked, and it's much easier to spin the spider gears and the stub axle vs driving the ring gear to spin the pinion.


You might want to replace the rear output shaft bushing to reduce that play in the yoke. You can do it without removing the TC from the truck, if you have a puller that can slip in there to pull it out.


As for the vibration, maybe the driveshaft isn't balanced, or one of the u-joints didn't quite get installed right (say, a pin fell over so it's not centered).
 

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Discussion Starter #3
The front driveshaft shouldn't rotate much, if at all, as the gear driving the chain in the TC is free to spin in 2wd mode, and the front differential is unlocked, and it's much easier to spin the spider gears and the stub axle vs driving the ring gear to spin the pinion.


You might want to replace the rear output shaft bushing to reduce that play in the yoke. You can do it without removing the TC from the truck, if you have a puller that can slip in there to pull it out.


As for the vibration, maybe the driveshaft isn't balanced, or one of the u-joints didn't quite get installed right (say, a pin fell over so it's not centered).
Thanks for reply,yeah I got thinking afterwards that the fact the vibration changes with throttles/pull weight that yeah it wouldn't be the front even if it did somehow spin when it shouldn't.

And yeah next thing to do would be the bushing In a series of elimination. we do have some pullers at work but I'm unsure of anything that may work for that bushing.

Driveshaft wise you never know but I'd think I'd have a constant vbration again from out of balance lie my last shaft, u joints seem fine, the only thing I can think of is that my rear diff input yoke, the u joints didn't fit snug, she would move Side to side by approx 1/8" or so, so I had centered it as best I could within that, maybe that's even an issue. I was thinking to jack stand it and run it up to speed to see if I can feel anything resonating.
 

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Well, what you say about the rear yoke sounds like a problem. If it's like mine (with the bolt on straps to the yoke), there should be 2 tangs that the u-joint just fits between, with not much movement possible by the u-joint, then it's strapped in place.


You may have installed the wrong u-joint (as the spacing between the tangs doesn't normally change short of a direct high with something solid while driving).


I would suggest starting with figuring out why the u-joint has that side to side movement.
 

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Discussion Starter #5
Well, what you say about the rear yoke sounds like a problem. If it's like mine (with the bolt on straps to the yoke), there should be 2 tangs that the u-joint just fits between, with not much movement possible by the u-joint, then it's strapped in place.


You may have installed the wrong u-joint (as the spacing between the tangs doesn't normally change short of a direct high with something solid while driving).


I would suggest starting with figuring out why the u-joint has that side to side movement.

Yeah Its not exactly normal like, I want to say between rust and before I had the truck there was a loose cap.... that somehow it may have pounded it around. the U-Joints used on the shaft are Identical to stock, in fact they are supposed to be IIRC, 0.008 thou wider which is very little. probably just my yokes worn. But one would think, and maybe I'm wrong, that it would create all the time vibration there as it wouldn't be centered, I'll check it on the blocks to see as well.
 

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Discussion Starter #6
Today I had put it on jack stands, Ran it up to highway speed, did not need to load it with the brakes as the vibration was felt, Went under the truck and also used a stethoscope to listen to the diff and transfer case, no noise from the diff but transfer case has some, However the vibration felt is certainly from the rear diff transfering it through the leaf springs to the frame. The wheels had some "out of roundness" So I removed them and re-ran the test, Vibration did not change. Afterwards I checked my U joint to find that the cups pushed out and the U joint now has 1/8 ish or under of play in it. So yeah next I'll have to source a new pinion yoke and continue from that, The driveshaft did show its self as being slightly un-true however that could be again due to the yoke.
 

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Discussion Starter #7 (Edited)
Well In my case it appears to of been the pinion yoke. I replaced it with a new one, nice snug fit, Ran it up on the stands again, I'd say ~80% of the vibration is gone, now the other 20% could be tires, It could still be the drive shaft a bit? I noticed it was not 100% round but It is a new one from gm... so knock on wood? I test drove at highway speed and felt no vibration at all anymore so I'm happy. I should of marked my pinion nut to the shaft for torque/orientation, I guess these diffs use a crush sleeve as to a spacer so there isn't a "torque" You go based on rotational effort of the pinion through tightening the nut against the sleeve. If anybody else reads on this, You set the pinion to a specified rotational torque then add the diff after, like a 1+1 = 2. I could not do that of course. I had hammered the shaft a tad to get the bearing to back out, then I used the impact and wiggled the pinion and used the impact, It went from some free play wiggling the pinion up and down to nothing, I then gave it 1 more ugga lugga :huh: and hopefully that'll do. Of course If I had thought to mark the nut to shaft I'd be able to be back to where it was before. As long as I did not over tighten it, It will be fine. I will keep an eye on it, I may opt to take it back 1 ugga lugga lol.
 
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