I have a serious thump (like a rubber muffled thump) when I accelerate in full time 4wd. It's only one thump and it does it again if I decelerate and accelerate again. I don't have that in 2wd. My rear lower control arms were changed last fall. I installed an OME lift about a month ago. Any idea anyone?

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2006 CRD KJ, 245/70R16 A/T KO, GDE eco tune, ARB bull bar, OME lift, AVIC-N4, turbo timer, pulsetech solargizer, Racor CCV3500, Racor 245R122 fuel head, Caterpillar battery, oem light bar, KC lights, HID fog lts, cb, ...

I have a similar problem currently and I'm thinking motor-mounts:
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=49882
The 4Wheel-only thing might be a red herring. Mine was like that at first, too, but eventually got more frequent and now sounds like a loud rattling in the engine bay any time the transmission is in gear and I'm stopped.

Check around that thread any others for ways to troubleshoot the motor mounts (pry-bar and a buddy or visual inspection, etc.) Also, it wouldn't hurt to inspect all the CV boots. The front drive-shaft has a tendency to tear its boot where it leaves the transfer case for no good reason and get dirt/debris in the joint and wear it prematurely.

Dan

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2005 Silver CRD Limited
245/75R16 GoodYear Duratracs
Fumoto drain | ProVent CCV Filter
Stanadyne FM100 filter | Cummins fuel pump
GDE Eco | SEGR | BoulderBars | FrankenLift | Frankenskids

That is a common u-joint/cv joint failure symptom, too.

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LOST # 633
'05 KJ 3.7L/6spd/241 245/75/16 MT's
'88 MJ 4.0L/AW4/231 SWB HPD30 & trac-loc D44 w/3.73's
A dirty Jeep is a happy Jeep

Same thing here when I'm stopped. I hear some rattlling. Also, when I'm accelerating at WOT, I feel something shudder around 3000 rpm. Make sense for the engine mounts. How do you check those?

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2006 CRD KJ, 245/70R16 A/T KO, GDE eco tune, ARB bull bar, OME lift, AVIC-N4, turbo timer, pulsetech solargizer, Racor CCV3500, Racor 245R122 fuel head, Caterpillar battery, oem light bar, KC lights, HID fog lts, cb, ...

There's one test I've done that make me think it might not be the engine mounts. I put the truck in drive and hold the brake with one foot and press on the accelerator with the other foot and no thumping. I release the brake and get the wheels turning and then I get the thump!!! I'm thinking around the frond diff. No thump whatsoever in 2wd. I do get a vibration when I stop and I'm in gear.

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2006 CRD KJ, 245/70R16 A/T KO, GDE eco tune, ARB bull bar, OME lift, AVIC-N4, turbo timer, pulsetech solargizer, Racor CCV3500, Racor 245R122 fuel head, Caterpillar battery, oem light bar, KC lights, HID fog lts, cb, ...

mine did me same thing turned out to be the front driveshaft

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2002 KJ 2.4L, 5 speed, tint,home-brew frankenlift, 31/10.50/15 Duratracs on soft 8s, Detours Backbone, Smittybilt XRC8, Homebuilt Lightbar w/ 4 100w lights
2004 TJ Rubicon 2 in bb genright hyline tube fenders 35 inch goodyear duratracs
2003 Chevy Suburban stock