Slight Vibration in Manual Trans after installing rear adams driveshaft

bdubnit

New member
Hey guys, just trying to pinpoint what's going on with my jeep... 2012 2dr JK man trans

My jeeps currently on a 3.5" rough country springs and fixed rough country front lowers, synergy rear uppers. front and rear adams driveshafts.

Replaced the front driveshaft a few years back and didn't seem to have any issues. Then had to replace the rear driveshaft this year. I didn't notice any sort of vibration or anything until i replaced the rear driveshaft. Added the rear adjustable uppers to fix the pinion angle like Adams suggested on a two door, but hasn't seemed to help.

The vibration is not persistent, but really only when i let off the gas in 3rd or 4th gear. It's a quick vibration i can feel in the stick shift and in the steering wheel. I can also feel it as I release the clutch into gear.

Could it be that I just don't have the pinion angle right still on the rear? Could it be the front pinion angle? Could the driveshaft be unbalanced? or maybe it's just a transmission/transfercase issue?

TIA
 

wayoflife

Administrator
Staff member
Sounds like your pinion might not be set just right. Might be a bit too low still. I would try to really work on this and get it on. If you're sure it is, could be you have an unbalanced shaft.
 

A.J.

Active Member
X2 When you accelerate at all rotational force tries to push the pinion up. Deceleration down. With a double cardian typical starting point driveline angle should be about 1deg < pinion yolk angle. You would want to lengthen the upper control arms.


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Whitarmy

New member
View attachment 338047

Would you say this is too low still?



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I put an angle finder on mine (drive shaft and pumpkin) to dial mine in. Bowed my springs quite a bit to get the angle that the drive shaft wanted. Added coil wedges to get the spring bow to not hit the track bar. Yours looks pretty close but a angle finder like the one Eddie uses in the DIY alignment write up will let you know for sure.


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bdubnit

New member
Just looking at the pic, yeah, I'd say it might look just a hair low but it's difficult to see 1° and that can make a big difference. You really need to use an angle finder to verify things.

I think that other pic is actually pre adjustable uppers. I just took a pic where it currently is. The rear uppers are brought in as much as possible but to the eye it looks like it’s a little high in this pic? Maybe i need to get some adjustable lowers to really dial it in.

IMG_0394.jpg

If the driveline is to be 1degree<pinion angle, does that mean the pinion angle should point up just a tad? For example, Drive shaft at 11 degrees and pinion at 12 degrees?





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wayoflife

Administrator
Staff member
I think that other pic is actually pre adjustable uppers. I just took a pic where it currently is. The rear uppers are brought in as much as possible but to the eye it looks like it’s a little high in this pic? Maybe i need to get some adjustable lowers to really dial it in.

View attachment 338048

If the driveline is to be 1degree<pinion angle, does that mean the pinion angle should point up just a tad? For example, Drive shaft at 11 degrees and pinion at 12 degrees?

Yeah, that looks pretty much on but an angle finder will verify as much. I personally have always had better luck setting both pinion and driveshaft at the same angle. For the same reason why you'd get vibes on decel, you can get them on acceleration if you're up too high too.

With that said, you might want to pull your front shaft for testing purposes just to make sure the problem is with the rear shaft.
 

A.J.

Active Member
There is an angle finder app for your phone. I have used mine a few times. As Eddie said you might need to remove the front to take it out of the equation if adjusting the rear doesn’t work.

Of course there’s still a chance it’s not balanced quite right also. Drivetrain vibes can be a pain in the ass.

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Last edited:

wayoflife

Administrator
Staff member
Thank you guys for the replies! I will definitely remove the front driveshaft and tweak it some more to try and figure it out.


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No problem. Just so that we're clear, it could still be a shaft that's out of balance. Just trying to make sure before you start throwing money at a problem :)
 

bdubnit

New member
So quick update...

Now that i understand pinion angle a lot more i realized the front driveshaft was likely the main culprit. Disconnected it and the majority of the vibrations went away. Am now getting just a small vibration in second on decel but i think i can attribute that to the rear drive shaft pinion angle.

The crazy part is I’ve had the front on for a few years but the stock rear driveshaft must have been masking any vibrations.

Here’s a couple pics showing the rear angles. Just want to double check that this is a good spot to check the pinion’s angle?

IMG_0463.jpg IMG_0465.jpg




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A.J.

Active Member
No the casting is not flat. You need to measure it on the pinion yolk. It looks a bit high to me but pictures are hard to tell sometimes.


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wayoflife

Administrator
Staff member
As mentioned, you cannot measure pinion from the base of the housing like that. Looking at your pic, your pinion looks high. Rotate your pinion until the top of the u-joint is pointing up. Place a socket on top of it to give you more more room to work with and then place your angle finder on top of it.
 

Samuelh3

Caught the Bug
As mentioned, you cannot measure pinion from the base of the housing like that. Looking at your pic, your pinion looks high. Rotate your pinion until the top of the u-joint is pointing up. Place a socket on top of it to give you more more room to work with and then place your angle finder on top of it.

Tips like this is why I love this forum. Using a socket as a base for my angle finder...genius!


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