Drive Line Vibrations - Transfer Case Angle / MML?

The_Heep

The_Heep

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OK fellas…I need a little help.

Over the years I’ve updated my 97 TJ, and this last update has me chasing my tail. I’m getting drive line vibrations at low speeds, 20-30mph, also it reoccurs again at higher speeds, 60-70mph, with subtle pulsating vibration. It started after a belly-up skid install. I installed a UCF skid plate, and a SYE, with a new Tom Woods rear drive shaft.

I’ve adjusted my rear control arms and drive shaft angles to try to eliminate the vibes, but no luck. I finally had time to take it to a local 4wd shop, and they thought, that my angle from the transfer case to the rear drive shaft might be too steep?

So…if my angle from the transfer case to the rear drive shaft is too steep, will increasing the MML help with that angle? Years ago I installed a JKS 1.25” Body Lift, with a 1” JKS spacer MML, with the OME Lift from Dirk @ DPG. I don’t know much a MML affects the angle out of the transfer case, would a M.O.R.E. 1.5” or a massive 2” MML help!? In the mean-time I was going to add some spacers to my skid plate to see if dropping it back down eliminates the vibes. My concern is that’s not a long term solution. I see UCF makes a Low-pro transfer case mount…but there seems to be some design issues with that, with a 97-Auto? Will upgrading MML from the current 1” to a 1.5” M.O.R.E. lift be enough, to change the angle or 2"?

Any other ideas?

’97 TJ
4.0L
32RH
4.56 Gears
Dana 30 – Lunch Box Locker Chromaly Shafts, Black Magic Breaks
Dana 44 – ECGS Rear with Detroit Locker,with the Rear Disc Brake upgrade
OME lift 2.5”
1.25” JKS Body Lift
1” JKS MML Spacer
Metal Cloak Adjustable control arms
UFC Ultra High Clearance Skid
SYE – With Tom Woods Rear drive shaft…and front Tom Woods Drive Shaft
Currie Currenctlync
Currie Anti-Rock
35"x12” Micky Thompsons
 
Does this help?

20240312_154239.jpg


20240312_154234.jpg
 
Figure out if it's the front or rear first. You're rear angles don't look way too much. Mine look worse (Savvy TT = very tucked) with no vibes, but it took a long time to dial it in. I also have a SS SYE though.
 
How long have you played with the angle? If vibes only happen under load, at least you know the direction you have to go. I also have a 1.5" MML btw but I'm not convinced it did much. My SS SYE did fix all my vibes, but I have an 8.8 which has a longer pinion mounting have and it's also offset more than a Dana 44 so those count against me.
 
Thanks. So are you saying since I only get vibes under load, I should pitch my pinion up more?

Help me understand. I haven't adjusted the pinion angle since before I put the jeep away for the winter. Last fall, if I remember correctly I adjusted up to 4 degrees both positive and negative to see if I could find happiness. I'm certainly up for adjusting it again.

But I was curious about if the transfer case to drive shaft angle could be the issue.

Thanks again...vibes! Argh.
 
The_Heep said:
OK fellas…I need a little help.

Over the years I’ve updated my 97 TJ, and this last update has me chasing my tail. I’m getting drive line vibrations at low speeds, 20-30mph, also it reoccurs again at higher speeds, 60-70mph, with subtle pulsating vibration. It started after a belly-up skid install. I installed a UCF skid plate, and a SYE, with a new Tom Woods rear drive shaft.

I’ve adjusted my rear control arms and drive shaft angles to try to eliminate the vibes, but no luck. I finally had time to take it to a local 4wd shop, and they thought, that my angle from the transfer case to the rear drive shaft might be too steep?

So…if my angle from the transfer case to the rear drive shaft is too steep, will increasing the MML help with that angle? Years ago I installed a JKS 1.25” Body Lift, with a 1” JKS spacer MML, with the OME Lift from Dirk @ DPG. I don’t know much a MML affects the angle out of the transfer case, would a M.O.R.E. 1.5” or a massive 2” MML help!? In the mean-time I was going to add some spacers to my skid plate to see if dropping it back down eliminates the vibes. My concern is that’s not a long term solution. I see UCF makes a Low-pro transfer case mount…but there seems to be some design issues with that, with a 97-Auto? Will upgrading MML from the current 1” to a 1.5” M.O.R.E. lift be enough, to change the angle or 2"?

Any other ideas?

’97 TJ
4.0L
32RH
4.56 Gears
Dana 30 – Lunch Box Locker Chromaly Shafts, Black Magic Breaks
Dana 44 – ECGS Rear with Detroit Locker,with the Rear Disc Brake upgrade
OME lift 2.5”
1.25” JKS Body Lift
1” JKS MML Spacer
Metal Cloak Adjustable control arms
UFC Ultra High Clearance Skid
SYE – With Tom Woods Rear drive shaft…and front Tom Woods Drive Shaft
Currie Currenctlync
Currie Anti-Rock
35"x12” Micky Thompsons
Click to expand...

How long is your rear driveshaft?
What’s your rear pinion angle?
What’s your rear driveshaft angle?
 
Thanks fellas. I'll get measurements this weekend.

Skylines...I have a similar angle gauge..yes works good, just not good enough for me to figure this out...I guess! 😀😃🙂
 
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Let me know if these pics help.
Rear Axle 16.2 degrees at ride, measuredbat the flat area behind the axle.
Then I zeroed it out. Then measured the drive shaft at 2.5 degrees...compared to the zeroed out rear axle.

Measured the drive shaft at approximately 17.5".

20240313_201751.jpg


20240313_201803.jpg


20240313_201820.jpg


20240313_202131.jpg
 
Should I have set my axle 2.5 degrees "above" my drive shaft? Right now as you can see in my pics it's "under" 2.5 degrees...if that make sense.
 
The_Heep said:
Should I have set my axle 2.5 degrees "above" my drive shaft? Right now as you can see in my pics it's "under" 2.5 degrees...if that make sense.
Click to expand...

Makes sense. First, from the length of your rear driveshaft you should be able to dial out these vibes. Those angles are not excessive. 25* or more is excessive. You’re at 16*. Second, you should raise your pinion 1.5* so that the driveshaft measures only 1* lower than the axle (pinion). You can do this by lengthening the uppers, shortening the lowers, or a little of both.
 
Last edited:
I cam make that adjustment...I'll be honest, I'm pretty sure last fall I when from 0* to 5* trying to eliminate the vibes, with no luck...but it's easy to adjust.

Which is why I was questioning the angle from the transfer case, and axle angle should be 1* "under" or maybe "over" the drive shaft.
 
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