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I've got the "post-lift thump"...has anyone figure
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Author:  LibertyCRD [ Mon Dec 05, 2005 11:40 am ]
Post subject:  I've got the "post-lift thump"...has anyone figure
I lifted my '05 KJ with the 1.5" front/2.0" rear Daystar lift. After putting about 1,500 miles on it that way I have developed a "thump" coming from the rear of the vehicle when I hit small bumps in the road. It sounds as though something is loose. But I checked the lug nuts on my spare tire, checked my shock bolts, inspected the undercarriage for leaks and loose bolts, etc. And I can't find anything wrong.

Today I read on another forums that many people are having this same thumping noise after lifting their KJs. Seems to be mostly 2004s, but maybe that's just because only 2004 owners are reporting it. Mine is '05 and I have it.

So anyway, does anyone have a clue what is causing this unusual thump?? It's not very loud, but loud enough to be noticeable. It's a little scary sometimes because it sounds like something is loose...but it has only started since putting on the lift. Anybody know?? :?
Author:  JJsTJ [ Mon Dec 05, 2005 12:03 pm ]
Post subject: 
Does your 05 CRD have the vibration dampner on the rear diff? Check that out, the rubber portion of it can shrink or move around allowing the metal pieces to move causing noise. Also, if you have gone wheeling and bent the bracket for the dampner, it can contact the rear sway bar and make noise. (speaking from experience here, mine has been removed for a while now due to being bent)
Author:  Calvin56 [ Mon Dec 05, 2005 1:06 pm ]
Post subject: 
I know you allready did this, but check your shock mounts again. I had the same problem, told everyone I checked the mounts multiple times. Out of frustration I tried tightening the shock mounts again- I torqued down a little harder, and no more thunks.
Author:  LibertyCRD [ Mon Dec 05, 2005 2:13 pm ]
Post subject: 
OK, well it's 29 degrees here right now and I hate working on the Jeep in the cold, but I'm worried that if it is the shock mounts that they could work themselves totally loose over time. So I guess when I get home from work today I'll jerk the rear tires off the KJ and torque these shock mount bolts down real good. See how that goes for a while...

Does anyone know what the bolts should be torqued to?? 65 ft/lbs??
Author:  W3CSX [ Mon Dec 05, 2005 6:57 pm ]
Post subject: 
[quote="Does anyone know what the bolts should be torqued to?? 65 ft/lbs??[/quote]

Directions with my Frankenlift:

80 lb-ft Upper mounts
85 ib-ft Lower mounts
Author:  Skyjump136 [ Mon Dec 05, 2005 7:29 pm ]
Post subject: 
I actually bent a shock bolt once. No matter how much I torqued them down the thump wouldn't go away. I finally removed it and there was a very slight curve to one of the bolts. I replaced all 4 bolts with grade 10 bolts and I've never had a problem since.

Also, what type of shocks to you have?
Author:  LibertyCRD [ Mon Dec 05, 2005 9:36 pm ]
Post subject: 
Well it could be my bolts then too. Because I'm running Rancho shocks, and all my bolts were tight. So who knows?? :(
Author:  LibertyCRD [ Tue Dec 06, 2005 3:33 pm ]
Post subject: 
Well I tightened up all my shock bolts. None of them appear to be bent or damaged. Actually they were all still pretty tight. Thumping noise is still there. Any other ideas?? :( I just don't know what else it could be...
Author:  JJsTJ [ Tue Dec 06, 2005 4:09 pm ]
Post subject: 
JJsKJ wrote:
Does your 05 CRD have the vibration dampner on the rear diff? Check that out, the rubber portion of it can shrink or move around allowing the metal pieces to move causing noise. Also, if you have gone wheeling and bent the bracket for the dampner, it can contact the rear sway bar and make noise. (speaking from experience here, mine has been removed for a while now due to being bent)

:roll:
Author:  LibertyCRD [ Tue Dec 06, 2005 4:29 pm ]
Post subject: 
Sorry...forgot to mention that. Mine was fine...not damaged at all. Doesn't hit the sway bar. All looks well there. I'm clueless here....
Author:  Skyjump136 [ Tue Dec 06, 2005 7:54 pm ]
Post subject: 
Take off one shock at a time and drive around the block. If the noise disappears there's your problem...
Author:  LibertyCRD [ Fri Dec 16, 2005 9:15 am ]
Post subject: 
OK well I've pretty much eliminated the shocks as the source. I'm really starting to think it's my rear gate. Seems like I read a thread somewhere and a guy had some trouble with his rear gate getting loose or out of adjustment and then it made noise when it was jarred around. Do you guys know if there have been any reports of that happening other than that one guy? I guess I'll have to check all the bolts on my rear gate and inspect the latching mechanism. Maybe I'll find the source of the "thump" there... This is getting annoying..
Author:  Skyjump136 [ Fri Dec 16, 2005 3:19 pm ]
Post subject: 
My rear gate definitely makes some noise. I think you'll find that on most KJs once they have a few miles on them.
Author:  ManicMechanicJoe [ Fri Dec 16, 2005 11:38 pm ]
Post subject: 
When I put a larger tire and CB antenna and spotlight on my reargate I got a thumping noise. No rear lift yet (rusty's is on the way!!!). My rear bolts were fairly loose so i tightened them and the problem dissapeared. BTW it took about 3000 miles with the larger tire and everything on there to make the noise.
Author:  greiswig [ Sat Dec 17, 2005 12:06 am ]
Post subject: 
I have it, too. I got a Rockfather II lift, torqued to spec, and immediately got more noise from the rear. Thumps and bumps when going over minor bumps at lower speeds.

This wasn't happening before, and the only change is the lift. I suspect the Doetsch tech shocks as being the source of the problem, and may disconnect them to prove it. But...given that the urethane bushings will transmit more noise to the chassis, and given also that the shims inside the bushings were too large for the bolts, I wouldn't be surprised to find that those two problems together are creating the noises.

Anyone find shims that are the RIGHT size?
Author:  greiswig [ Sun Dec 18, 2005 4:24 pm ]
Post subject: 
greiswig wrote:
I have it, too. I got a Rockfather II lift, torqued to spec, and immediately got more noise from the rear. Thumps and bumps when going over minor bumps at lower speeds.

This wasn't happening before, and the only change is the lift. I suspect the Doetsch tech shocks as being the source of the problem, and may disconnect them to prove it. But...given that the urethane bushings will transmit more noise to the chassis, and given also that the shims inside the bushings were too large for the bolts, I wouldn't be surprised to find that those two problems together are creating the noises.

Anyone find shims that are the RIGHT size?


Suspicions confirmed: I went to my hardware store, bought some rubber stoppers and made two new bushings for the upper shock mounts on the Doetsch Tech shocks by drilling out the centers to be a tight fit on the 12mm bolts. All the suspension noises disappeared.

I think the noises are a combination of factors: too-hard urethane, too large a steel sleeves so there isn't a tight fit against the bolts. I'd like to find a softer urethane that has the right inner diameter, since a steel sleeve isn't very good isolation even if it IS the right size. Better to have a thicker layer of urethane. Don't know if anyone makes such an animal, though, and I have no idea how long rubber stoppers can be expected to last...but I bet it won't be long.
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