1996 2DR XJ with 242/8.25

Hi guys, I just finished installing a 3" RC lift (F coils/shocks and R leaf packs and shocks, Iron Rock DS track bar) and it rides great *except* for a 25-30 Hz "rumble" once I hit 25 mph. At 27 mph, the rumble is gone. It sounds like I have bass in my car, it's pretty loud. It doesn't make noise from 0-24 mph and from 27-65 mph.

Here's my rig: https://i.imgur.com/Wa18KsY.jpg

I have a 3 deg shim on the rear leaf pack. No transfer case drop. My pinion angle looks OK, it's maybe off by a tad.

Would a TC drop solve the rumble? Honestly, it's not that bad. I just like everything perfect!

 

Lets see the pinion angle, that shim could be the issue. It's usually recommended to not put anything that will change driveline/pinion angles on until you know you'll need them

 

With the 3* shim I wouldn't think that a TC drop kit would be required either but a cheap try if you can not find the reason. The 3" lift isn't that high was everything in your front end ball joints, tie rods, ca bushings in good shape before the lift. Any weak points there will show more after a lift than before very quickly, these may cause your problem or not, the just 25mph doesn't tell much.

BTW it helps if you will fill out the info on your XJ at least the year then eng./trans helps others when ask questions.

 

Updated my original post to include: 1996 2DR XJ with 242/8.25

The 3 deg shims came with the Rough Country leaf pack.

Here are pics of my driveline:

 

Yup, shims are causing the issue. Here's a picture of a proper pinion angle. The pinions should be parallel to each other, not trying to straighten one out.

 

So would it be better to:

1. Drop transfer case 1" to make the pinion angles more parallel. I believe this drops the pinion and would make the front and rear more parallel.

2. Take off the 3 deg shims on the rear leafs

Obviously 2. is more work at this point.

 

Take the shims out, it shouldn't be too hard since the u bolts are new. It'll actually be less work than possibly breaking the crossmember bolts to install the drop. You need to have the pinions parallel, dropping the crossmember won't make much of a difference