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virtuoso 07-01-2010 09:31 PM

Clunk in driveline when accelerating
I would love to get to the bottom of this.

I have the popular clunk in my '06 LJ Rubicon Auto, RE 3.5" short arm with 1.25" BL & 1" MML, adjustable uppers front and rear. It is almost reproducible when accelerating in first from idle. Sometimes you can hear it when letting off the gas only in first, high RPM's. With several speed bumps in my neighborhood I hear it very often and it's driving me up a wall.

So far I have checked engine and tranny mounts, flipped rear shocks, tightened exhaust mounts, and found no loose parts floating around in back :)

It does not occur when turning, which made me think it was the control arm bushings - especially after I read a post about RE bushings failing. I have poly at frame and SF at axle. Tightening to spec this evening did nothing for the noise.

Under no load the rear driveshaft has some play and I have heard conflicting information about how much backlash should exist in a driveshaft under zero load. Some say a slight turn and others say none at all. If I rotate the rear shaft under no load it makes a strikingly similar sound. Could it be internal to the tranny or TC? A chain that needs adjustment? Rear-end? Hard to believe the issue would be internal on a daily driver with under 40K.

I have yet take off my rear shaft and test only front to isolate, but I am willing to bet the noise doesn't occur as there will be no rotational torque to the rear, the place on the vehicle producing the sound (as far as I know).

Any comments/questions provided would be greatly appreciated.

virtuoso 07-06-2010 09:04 PM

I was sure someone would have some thoughts on this topic.

Side note, while getting my tires rotated at the shop today I noticed some "play" in my rear wheels. By this I mean by turning one side, the other took some time before it caught up and turned the opposite way. I realize the hubs should take some amount of turn to sync up but not as much as I experienced. Later, I had my wife's Commander up on the lift and noticed significantly less turn before the other side "caught".

Again, my clunk does not occur when turning. I am not sure if this vehicle (2006 Rubicon with factory lockers) has limited slip but it seems to me that the noise could be a result of the drive wheel and shaft engaging.

I have not put the vehicle in 4lo and locked the rear lately but last I recall when I did the noise was still present.


drivebytruckerz 07-06-2010 09:08 PM

Put it on 4 jack stands and have someone give it a look see while you are inside giving it gas. You might have a broken mount that doesn't necessarily look broken.

virtuoso 07-06-2010 09:19 PM

Thanks for the addition. Any specific mount you have in mind?

drivebytruckerz 07-06-2010 09:27 PM

No, it really could be anything. My buddy had a mount that was there, but he saw it move using this method, and it didn't have a bolt in it.

Just get someone to stare straight down the engine with the hood open and look for movement when you rev it up. Then do the same from below looking up at the drive-line...

Ken Steele 07-06-2010 10:55 PM

Did you do any mods to the Jeep immediately before this started? Do you have a gas tank skid installed? Can you feel the "clunk"? If so, where do you feel it (seat, floor board, steering wheel, shifter, etc...)?

Wench 07-07-2010 07:24 AM

shot in the dark here but check your driveshaft. could be out of balance...

virtuoso 07-07-2010 07:49 AM

Thanks for the input DBT, Ken and Wench.

rtread 07-07-2010 09:17 AM

I had something similiar, the guys at the Jeep dealership finally found it. The transfer case mount was loose.....both nuts were very loose, they tightened them and noise ceased. It was driving ME crazy!

adkjoe 07-07-2010 09:45 AM

If your drive shaft has play check the u-joint. I had the same problem, cluncking when accelerating and over bumps. My DS had some play, tracked it down to the front u joint. $20 and a 30 min later no more clunking.

virtuoso 07-07-2010 09:45 PM

Thanks for the additions. I have checked the u-joints but not thoroughly by taking the rear shaft off. I have checked the tranny mounts.

I had it in 4Lo and locked today and in F and R, as soon as it was placed in gear and torque was applied, both front and rear clicked into place. This makes me think the control arm bushings need servicing as well, but they produce more of a click than the hard clunk I feel in the rear of the vehicle. This is really pissing me off.

virtuoso 07-09-2010 09:31 PM

YouTube - Driver's side control arms

Around 40 seconds you can see the upper arm at the frame almost coming out of the socket. There must be at least a 1/4" of movement. My lower arm bushings on both sides are cracked - Rubicon Express is sending out 4 new bushings for the lower arms - so I am not sure if the noise is coming from the uppers or lowers, but I may have tracked it down. Thanks for everyone's input.

06TJinVA 07-10-2010 08:44 AM

I have to exact same clunk when I get on it hard from 1st to 2nd. It feels like its in the driveline right under the middle console. It hasnt really cause any problems, just worries me when I do it which I try not to if I can help it.

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