another possible drive line vibe question

desertrunner

Active Member
so after my axle swap and re gear i have been trying to think of things that might be causing a small vibration i have been feeling, just looking for confirmation on what i think is going on.

background i have a PR44 Unlimited with 4.88 and all stock front control arms. pinion angle is 2.5* caster 7.5* and the drive shaft is at 4.5* (2* difference from pinion angle).

I am getting a very high frequency deep bass vibration starting at about 45MPH that is consistent through 70, that has a resonance about once/2 sec. nothing violent but enough to tickle the feet a little on the floor and to buz an empty can in my cup holder.

I pulled the front shaft and took it for a drive. the vibe at 45 MPH went away but starting at 60 consistent to 70 im still getting a very similar vibe as described above just enough to buz a can in my cup holder.

first thought is the 2* difference in pinion and driveshaft angle. If i get adjustable uppers i can get them the same leaving me with 4.5* pinion and 5.5* caster but that still wouldnt change the vibe i have with the front shaft out.

second thought was maybe im just feeling vibrations from the tread on the coopers on the pavement so i dropped the pressure 5PSI lower and that didnt change a thing.

my next thought is to pull the rear shaft next and check that too but i suspect im going to end up with the same vibe at 45MHP that i had before.

so before i go spending money on front uppers, could that 2* difference in the drive shaft and pinion cause that vibe im feeling? Or am i worrying about something that isnt that big of a deal and its just a product of driving a jeep with MTs and 4.88s?
Last thing i want to do is grenade my Rubi T-Case due to a vibration i failed to address. :icon_crazy:
 

WJCO

Meme King
Does the higher speed vibration change tone slightly during accel/decel? If so, it's powertrain related. If you were to have the vibration and put the vehicle in neutral and the vibration was still there, it's likely a tire/wheel or wheel bearing issue.
 

jorgelrod

Hooked
How high is your lift? PR44U with 3.5 inches or lower will most definitely need adj upper control arms to adjust the angle.
 

desertrunner

Active Member
Does the higher speed vibration change tone slightly during accel/decel? If so, it's powertrain related. If you were to have the vibration and put the vehicle in neutral and the vibration was still there, it's likely a tire/wheel or wheel bearing issue.
You know I didn't try that and I can't remember when I got off the freeway last night if it was still there off the gas.
How high is your lift? PR44U with 3.5 inches or lower will most definitely need adj upper control arms to adjust the angle.
I'm at like 2" maybe a hair more. I know it was a long shot that it would set up right, but don't know until you try. I know for sure if I get adjustable uppers that I can get the driveshaft parallel to pinion but I just wanted to see if only 2* really might make that vibe

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JMFK

New member
I had/have this same problem. I have a 4in lift with a PR44. I adjusted caster to align pinion and shaft and my vibration (exactly as you described it) went from being the worst at like 65mph up to 75mph. Guess I need to adjust more. Also I’ve noticed it’s more prominent when I go up hill, not accelerating up hill, just maintaining speed up hill.

I should also say that since the vibration changes when I adjusted the front I’ve never investigated if the rear shaft and pinion alignment is to blame.

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desertrunner

Active Member
I had/have this same problem. I have a 4in lift with a PR44. I adjusted caster to align pinion and shaft and my vibration (exactly as you described it) went from being the worst at like 65mph up to 75mph. Guess I need to adjust more. Also I’ve noticed it’s more prominent when I go up hill, not accelerating up hill, just maintaining speed up hill.


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Well at least the upper front arms are the cheaper of set to buy haha. I guess I'll start there see if it help. I don't drive faster than 70 in this thing I just really don't want to blow up a transfer case

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JMFK

New member
Well at least the upper front arms are the cheaper of set to buy haha. I guess I'll start there see if it help. I don't drive faster than 70 in this thing I just really don't want to blow up a transfer case

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The thing I hate the most is that sometimes the vibration is so subtle I convince myself that I’m making it all up. But then I had to change my pinion seal after only 20k miles and am thinking maybe I’m not imagining it.


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desertrunner

Active Member
I will say for sure though that the vibration wasn't there before the re gear. And I drove it hwy speeds with the front shaft out plenty before I got the gears done. So I figured the vibe at 45 was the front shaft. Conformed that. But that vibe at 60 has to be something in the rear after the re gear. Which sucks considering the shop I went to is 5 hours away and their labor ain't cheap

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desertrunner

Active Member
ok did another test drive, front shaft still out and got some better info.

small buz in the floor i can start feeling around 50, consistent to 80, audible deep bass buz that buzzes the can in my cup colder starts around 60 and actually kinda goes away at 80. when driving at 75 gas applied i have the audible buz. when i let off the gas it goes away but i can still feel it in the floor coasting all the way until 60. as soon as i get back on the gas the audible bass buz comes back.

So what i decided im going to do is go ahead and buy adjustable uppers and get the pinion and driveshaft nice and straight. That should at least take care of the vibe at 45 that i was feeling before i pulled the front shaft.

As long as that works then ill go ahead and pull the rear shaft and see if maybe something in the rear is causing the vibe at higher speeds. if im still getting that vibe at high speeds ill start messing with the tires, rotate them see if it changes, maybe get them re balanced, mess with the pressure a little bit more and see where that gets me.
 

desertrunner

Active Member
For what it's worth, I had a vibration after my regear that I could've sworn was from the front driveshaft or, possibly the transfer case because of how things felt. Turned out it was the new bearings in the rear were eating themselves up.

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Build Thread - Adventures of Fiona - https://wayalife.com/showthread.php?t=47407

that is quite possible in my situation too with all the new bearings that were put in during the re-gear,

how did you end up finding out the bearings were eating themselves up? was it all 3 or just pinion or carrier?
i really dont want to go back to the same shop that did the work to be honest so if it does come down to it i may try to do the bearings myself.

i am pretty convinced the vibe at 45 was the front shaft so i am going to at least fix that one with control arms, if it turns out im still getting the vibes at high speeds when i pull the rear shaft i may have to look into the bearings. I just pulled the cover after gear break in and i didnt see anything concerning but maybe i overlooked something
 

BaddestCross

Active Member
The shop finally pulled the rear apart after not finding problems anywhere else. It really was a weird noise and vibration. I first thought it was the front diff so I pulled the shafts and it was still there. As it got progressively worse, it felt like it was the t-case because I felt it in the console. Even the installer thought it was something in the front or t-case so he went crazy tearing down everything before going to the rear.

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Build Thread - Adventures of Fiona - https://wayalife.com/showthread.php?t=47407
 

desertrunner

Active Member
The shop finally pulled the rear apart after not finding problems anywhere else. It really was a weird noise and vibration. I first thought it was the front diff so I pulled the shafts and it was still there. As it got progressively worse, it felt like it was the t-case because I felt it in the console. Even the installer thought it was something in the front or t-case so he went crazy tearing down everything before going to the rear.

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Build Thread - Adventures of Fiona - https://wayalife.com/showthread.php?t=47407
Hummm ok well the shop I went to is 5 hours away and there were a few things that came up during the instal that doesn't give me confidence that I want to take it back to them.

I'm going to start with the getting the front all squared away (front uppers already ordered) and pull the rear shaft and see what it does. I'll report back with what I find in a week or so

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MSJKU11

Caught the Bug
From what it's worth I had a vibration after my regear that turned out to be my toe-in not being setup correctly. Not sure why it didn't cause any vibrations before my regear but perhaps it was amplified after. Just in case nothing else works.
 

desertrunner

Active Member
From what it's worth I had a vibration after my regear that turned out to be my toe-in not being setup correctly. Not sure why it didn't cause any vibrations before my regear but perhaps it was amplified after. Just in case nothing else works.
I will definitely keep that in mind too thanks!

I would suspect a toe in or out issue would manifest more off the gas since the weight would shift forward instead of worse on the gas like I'm feeling. But if I still can't track it down I'll check that as well.

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BaddestCross

Active Member
Hummm ok well the shop I went to is 5 hours away and there were a few things that came up during the instal that doesn't give me confidence that I want to take it back to them.

I'm going to start with the getting the front all squared away (front uppers already ordered) and pull the rear shaft and see what it does. I'll report back with what I find in a week or so

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Good luck. Hope you get it figured out. Oh, to answer your original question, I believe it was the pinion bearing that went first which caused the pinion to start eating itself.

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Build Thread - Adventures of Fiona - https://wayalife.com/showthread.php?t=47407
 
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