4 Wheel Drive/SUVs: Thump Noise on Newly Lifted Jeep, adjustable track bars, pin eliminators

Question
Dear Expert,

I have recently gotten the Jeep Bug, I have had many off road vehicles in the past and was brought up in a very out-door rural area. The brand new 2004 Jeep Wrangler by far out performs all my previous recreational vehicles with out any modifications. However I had to modify it even more! I wanted a little more lift and was told that Fabtech had the best. So I put 31" BFG All-KTOs, a 2.5" adjustable coil springs with 10-stage Fabtech shocks, adjustable track bars, Bar Pin Eliminators. The height ended up being all most 3.25" and it looks assume. The overall ride is great, I am getting no vibration and the steering is excellent.

However I am getting a bump sound coming from the rear, it is driving me crazy, the folks who put the lift on say they can't feel it. If the wrangler in smoothly knocking around the trails, it is a nice ride, if I go over sharp bumps (pot hole type) I hear a knocking. Everything I have done has been professionally installed and appears to be tight. I even rode in the way back of the beast today while my wife drove it, do I need a shrink or what. Tonight I even had he on the back bumper jumping while while I was underneath it trying to see if I could tell where it was coming from.

I thought the bar Pin Eliminators would have cured it but it only helped a little or it's in my head. I have been trying to look at every web site and can't seam to find an answers. I honestly do not remember the sound or bump before the lift kit.  I have spent a fortune and have all new kits and modifications. Please help!

Any ideas anyone can though my way please do...

MTJeep...  

Answer
Michael,

This can be anything from a faulty shock mount, to a loose body bushing.  If the bar pin eliminators seemed to help, I would start there, and look to see if you can see any obvious rub marks on any of the components.  Check all of the bolts, and connectors that you can to make sure there are no loose components.  Look your springs over very carefully, and see if one of them might show some marks from hitting the frame, or other components when they are flexing.  You may have a rubber or neoprene bushing that is worn, and allowing some movement in a suspension component.  A bushing, can, also be too tight, and creating a bind, unloading under a sharp movement such as a pot hole.  I have seen the slip yokes in drive lines get in a slight bind, and make this type of noise when they unbind.  Since the sound is occurring during a sharp bump, I doubt if you could find the noise by jumping on the bumper.

This type of noise can be very deceiving, as it may be projected along a component such as the frame, or drive lines.  If this is the case, it may not be coming from the area that you seem to hear it from.  

Carl