Engelwood

Hello to all. Just to be clear, I have used the search option on this site and many others. I have scoured the entirety of the interwebs, forums, youtube videos etc etc.

Details - 1999 XJ, AW4, NP242, 4.5'' RC full Leaf kit, 1'' TC drop, 265/70r17 tires,JK wheels, 146k on the ODO.

Installed lift 2 weeks ago. I get a rumble/growl noise ONLY ON DECELERATION from 20+mph! You can feel it in the seat, floor and not really the steering wheel.

Started with the back

Popped Diff open, gears looks good, no metal flakes, rear axle bearings had no play, fluid was very thin, changed it with that primo lucas 75w140. Still, same noise.
Put the rear on jack stands and chalked the front while a friend sloooowly accelerated, noise comes from the middle..somewhere..

Read somewhere to take rear DS off and go FWD and see if that solved it, sure did! no more noise going down the road. U joints right? Ya put 2 Precision joints on front and back of DS, TODAY, installed DS back on...Same Noise...

Read somewhere that my TC chain could be loose/skipping teeth, makes sense. Under a load, no noise. When its in neutral/ no acceleration something is not happy. But everything feels tight and have never had it pop out of said mode, or anything funky.

I checked pinion angle, TC side is 4 degrees, rear is 10 degrees. I drained TC fluid today, it was black... Before I fill it back up Im going to see if that chain is good to go. ANYONE PLEASE HELP! I have become an alcoholic because of this jeep... But thanks in advance for the Tips

Radi

No noise before you installed the lift? What did you do with the slip yoke?

XJRed96

you driveshaft is the likely culprit. that's a big lift to install on a factory driveshaft with no modification. the fact that you only hear on deccel is almost a gurantee that it's the driveshaft. at that height you will need to install an SYE and possibly even shim the rear diff up a little bit. The vibration is likely being caused because the drive shaft isn't seated all the way back on the slip portion, instead it's probably sitting half way or less. If that doesn't make sense then you haven't searched enough. try searching "drive line vibrations after lift" and "SYE"

Engelwood

I want to hope it's the DS and me needing an SYE. That is the next step. Everything you said makes sense.
Saying I haven't used the search well enough is completely false. Litterally hours on it. Thanks for the replies, will update after I can actually find a front DS to use!