Clunking (transfer case?) noise when the jeep is moving

[ghst32]

I have searched and there are a lot of transfer case noise threads but I didn't find one exactly like the issue I'm having.

What I have is:

•2000 XJ

•6.5" Iron Rock Offroad lift

•Rugged Ridge Slip Yoke Eliminator on NP231 transfer case

•Custom drive shaft from Iron Rock

•Rear end rebuilt less than 20,000 miles ago


This set up has been on the Jeep for almost 2 years without problems. A week ago I started getting a noise from what seems to be coming from the transfer case.

I can only describe it as a repeating clunk/thump from what sounds and feels like it is coming from directly under my seat (transfer case area). The sound is very consistent and:

•happens only when the Jeep is moving/frequency follows the speed of the Jeep

•happens only in 2wd/seems to go away when in 4wd

•speeds up/clunks faster the faster the Jeep is rolling/slows down as the Jeep slows down

•is worse the more the Jeep is under load/accelerating

•completely goes away when the Jeep is driving and is popped into neutral

•at higher speeds makes for a very loud humming/vibration sound all through the inside of the cabin


The 3 U-joints (double cardan) on the rear drive shaft don't have any play when we unhooked it and inspected it. The Shaft coming out of the transfer case also has no play. We opened up the rear axle diff just to make sure there was nothing lodged in the gears and everything looks clean. It is now at transmission/driveline shop where they have opened up the transfer case and to everyones surprise cannot find anything wrong. At this point I have no idea what this could be. Any ideas would be greatly appreciated.

 

[clean4drxj]

Don't rule out loose crossmember bolts or control arm joints.

 

[Flyfisher]

Also check transmission mount at cross member...especially since it does it upon acceleration.

 

[ghst32]

Don't rule out loose crossmember bolts or control arm joints.

I will definitely check those. I'm not sure if that would be the issue though since it will do it at a 2mph roll.

The guy at Iron Rock Offroad just called me back and he is suggesting that maybe it is in the pivot ball/spring in the center of the double cardan.

 

[ghst32]

Also check transmission mount at cross member...especially since it does it upon acceleration.

I will double check that too. It does do it when I'm rolling to stop with no engine load on it though. It just clunks slower and slower as I slow down.

 

[clean4drxj]

Also if the transmount is bad it will allow movement in the drivetrain

 

[KingIce]

You can rule out the driveshaft easily by swapping the front ds to the rear and see if anything changes.

 

[ghst32]

Ok guys, it ended up being the ball/socket in the double cardan in the rear drive shaft. the bearings had fallen apart inside. How the driveline/transmission shop didn't figure this out is beyond me. I really appreciate all the input though guys.