Hi all,

I recently installed a RE 3.5 lift, and did the SYE conversion with tom woods rear shaft.

Recently took jeep on a road trip and noticed that around 60 mph a noticeable rhythmic vibration started and got worse around 70-75. I found it bothersome enough that I chose to drive 55 mph in the right hand lane with the intention of troubleshooting the issue when I got back.

Rear shaft is obviously new, with new joints. I also replaced front axle u joints. I didn't change the front shaft joins however, which is interesting because when I remove the front D/S 90% of the vibration goes away. So I'm thinking that it's either the drive angles with the front shaft, or the front shaft needs a rebuild.

I am unfamiliar with measuring pinion angles and drive angles, but before buying a new driveshaft I'd like to check them to make sure that they're acceptable.

I will be taking this car on several 1000+ mile road trips so absolutely zero vibrations is the goal.

The lift surely affected the drive angles, and I did not install any sort of shim on the rear axle, so potentially there is a slight amount of vibration originating from the rear shaft.

The front shaft, I feel like will be more tricky because i can't change pinon angles without also affecting caster.

Just looking for advice/help

Thank you

 

Get another front driveshaft

 

Went out to measure angles this afternoon, and while it may not be entirely the cause, I do think that these angles will cause vibrations, correct?

My understanding is that you needed/wanted 2° downward pinion tilt, relative to the driveshaft for two reasons, one when the rear loads the pinion will tilt up, and the 2° will bring it into alignment. The other reason that you don't want it completely flush, is that you need the needle bearings to move/spin to keep greased.

Using that understanding, the rear pinion needs to raise 8° to keep vibrations at a min, is this right?

How about the front?

I do intend to purchasing a new front D/S but it appears that my angles are incorrect, so I'd like to correct that as well.

Forgive the crude diagram.

 

Redbird , is your front diff an open or LSD or locked? you might try removing your front DS and run down the road at speed and see what you feel, this might eliminate the front axle as vibration source. The rear pinion and the rear DS should be 0 degrees (parallel to each other) with a tolerance of 3 degrees down, on the pinion side. closest to zero works best for me. Do you have access to a digital inclinometer? under 25 bucks at home depot. Much better than angle finder. very easy to use.

 

boy oh boy I need to read slower or understand better !! I missed that you did remove your front DS. Still check your rear pinion angle against your rear DS anyway. I would leave the front DS out until you checked and possibly corrected your rear DS angle.