Drive Line Vibration and Pinion Angles Post 2.5 Inch Lift

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BJeepTJ

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Joined
Aug 22, 2022
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Fort Collins, CO
New to this community with my New to me Jeep that is 24 years old.
I recently added a 2.5 Inch suspension lift with tier 2 Core 4x4 adjustable control arms and adjustable track bar to make sure everything was done correctly and within tolerance in hopes that post lift I would avoid the pitfalls discussed in this forum such as bad alignment, death wobble, crab walk, driveline vibration etc. We’ll to my dismay everything is perfect except the vibration around 40-50, or while accelerating between 2,3 and 4. Ironically at 65-70 smooth.
I thought I would share my findings in hopes to provide data for others and hopefully find a cure without a SYE kit and transfer case drop. Might be naive, but was hoping to avoid the normal corrections by using the adjustable control arms and get everything dialed in.
Rear
Pre lift
TC 6 degrees
Drive Line 7 Degrees
Pinion 7 Degrees
rear axle flat spot 82.5 Degrees

Post lift
TC 6 degrees
DL 26.9 (pre adjustment of control arms, the axle was 78, and the pinion was 12, and the drive shaft was 15. By lowering the pinion to achieve parallel, significantly increased the angle of the drive shaft. )
Pinion 6.9
I hoped that would balance DL, I realize the DL at 26.9 is steep but it was only a 2.5” Lift.

What has worked with others, read a lot of reviews that a 2.5 wouldn’t need any MML, TC Drop or SYE. The vibration is not extreme at all, just trying to get it as smooth as it was pre lift.

everything is check out, front caster is 6 degrees, axles are re centered, wheel base is back to OEM, track bars enabled the horizontal and vertical alignment of the axles and the track bar and

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Your rear driveshaft angles are too extreme which will cause driveline vibrations and premature U joint wear.
Last year I installed a 2" coil spring lift which created rear driveshaft vibrations due to the rear driveshaft angles.
I have heard that some Jeeps with a only a 2" lift DO NOT get driveshaft vibrations, but every Jeep is different.
In the interim I installed a transfercase drop of 1" to change the rear driveshaft angles enough to alleviate the vibrations.
In January I installed a G2 SYE and several weeks later installed a Tom Woods DC driveshaft.
Measured the difference in driveshaft to pinion angles at 3* and with two occupants the angle differences went to 1*.
After 9 months the angle differences between the driveshaft and pinion angles were the same and the driveshaft vibrations have remained gone.
 
I lifted my TJ by 2.5". I also did a 1" BL and a 1" motor mount lift. I am no expert, but I believe the latter may have helped me a little as I have not had any vibration issues. But as said above, this seems to be variable between Jeeps, so maybe I just got lucky.
 
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CharlesHS said:
Your rear driveshaft angles are too extreme which will cause driveline vibrations and premature U joint wear.
Last year I installed a 2" coil spring lift which created rear driveshaft vibrations due to the rear driveshaft angles.
I have heard that some Jeeps with a only a 2" lift DO NOT get driveshaft vibrations, but every Jeep is different.
In the interim I installed a transfercase drop of 1" to change the rear driveshaft angles enough to alleviate the vibrations.
In January I installed a G2 SYE and several weeks later installed a Tom Woods DC driveshaft.
Measured the difference in driveshaft to pinion angles at 3* and with two occupants the angle differences went to 1*.
After 9 months the angle differences between the driveshaft and pinion angles were the same and the driveshaft vibrations have remained gone.
Click to expand...

So you feel like it was worth cost? Did you do the work yourself?
 
I had a 2" bb lift and had to drop the skid 1/2"
Later did a 4" and had to do a SYE. My point is go ahead with the SYE and if and when you do a larger lift your already prepared.
 
taylormade73 said:
Those look like some old crusty original DS u-joints. The lift probably is exposing the fact they should be replaced.
Click to expand...

As @taylormade73 pointed out, your old U-joints might be part of the problem. Have you isolated it to which DS is vibrating? Some TJ’s with 2.5” lifts do well with a Motor mount lift and adjusting the rear control arms to get the pinion angle and output angle closer to matching each other.
 
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