2004 KJ Rear End Thump

Lilngineer · Nov 15, 2010

Hi-

I recently purchased my 04 KJ with 97K on it and have discovered a problem that I could use some opinions on. I have noticed when I accelerate quickly off a slow roll (ie punch), I get a loud thump, thud, slam kind of noise and feel from what appears to be the rear end. I also seem to notice it mostly when doing so starting to turn.

For example, I am leaving our condo complex to the main road rolling slowly, I see no traffic and hit the gas to turn out and get the thud.

It however only happens under this condition. Slow accelerations are fine.

Any ideas on what it could be? I am concerned it might be an issue with the rear axle. A local shop suggested control arm bushings. I also saw reference to a "boomerang" ball joint on the rear end in the forums. Thoughts?

I have just had a 4WD/transmission fluid service and have removed the front driveshaft for a cracked CV boot with no change.

Any help is much appreciated.

osufans · Nov 15, 2010

do you know anything about the history of it? aside from u-joints, you may have an aftermarket locker in the rear-diff which causes a similar noise. you can find out if you have one of those just by finding a gravel road or parking lot....if you only peel one wheel you don't have one.

ridenby · Nov 16, 2010

Check the "boomerang" balljoint among other things.

ericautopart · Nov 16, 2010

Check the rear drive shaft for play. It does sound like u joints..

Lilngineer · Nov 16, 2010

I just bought it so I don't have much history. It seems pretty stock to me. I had it to a shop over the weekend who thought it was the front drive shaft cracking. I did remove the shaft but the problem remains.

Next it's going to a driveline shop for a look. I'll be sure to have them check u-joints, boomerang, lockers etc

Lilngineer · Nov 18, 2010

Well I took my front driveshaft to a local driveline expert and asked them about the noise. They took a look at the rear driveshaft, u-joints etc and said everything seems normal.

The owner went for a ride with me and of course I couldn't quickly reproduce it. However, when I described the condition when it happens, he believes it is the transmission timing dropping from 2-3 down to first. He says it's briefly going into neutral and then catching while spinning into first.

He suggested I manually shift down when I anticipate it happening and see if it goes away.

They weren't very familiar with the tri-link suspension so I'm not convinced it might not be that.

Anyone have thoughts on this?

osufans · Nov 18, 2010

I do sometimes get a "bump" when the ****** downshifts on deceleration, but I don't notice it being anything too abnormal. Then again, I'm no expert in the operation of the 42RLE.

The only quirkiness that resembles what you are asking about in the first post, is sometimes when rolling to a stop, if I take off before I come to a complete stop, it hesitates to find the right gear, and will sometimes slam into gear once it finally gets there. But I definitely notice that from the transmission, not from the rear.

diyman · Nov 18, 2010

I'm beginning to think this is a KJ's common issue. If everything seems ok, I'd not loose sleep...
If nothing is known about maintenance history, I'd drop the ******, change transfer and diffs fluids, just in case...
Also, stock U/joints are non-greasable, I don't like them... Anyway, just IMHO

.

KornyBrad · Nov 18, 2010

LOL mine does the same thing and I was going to ask the same question. Glad I looked first. Sounds like it is a common issue. I think I'm still going to get the ****** fluid changed soon.

randrson · Mar 19, 2011

I'd still take a look at the upper ball joint on the tri-link. My 05 had on 76k when I bought it, the the ball joint was toast.

with it sitting on the ground, if you pry up carefully on the upper tri-link arm avoiding the brake line, you can see how much play is in the ball joint. there is a bit of rubber that isolates the ball joint center from the portion pressed into the arm, and when this rots away, it will thump on hard acceleration. \

A quick and dirty way to figure out if it the culprit is to put it in neutral on a slight incline and coast backwards, then pull the parking brake. If you get a good thump, that's the axle wrapping and banging the ball joint against the outer housing. (It was harder to tell that was my problem initially since mine is stick, and I had driven stick on almost four years.) if you find this is the problem, I got the complete new upper arm from autopartswarehouse.com for $130. It is from Crown, is made domestically, and aside from not having the Chrysler ID stamping, is exactly identical down to where the welds are located. I put it in last week and it made a huge difference.

tommudd · Mar 20, 2011

What some say is normal is not
Mine doesn't do it nor does several that I have driven after lifting them
Check the rear tri link, I have seen them bad enough that the ball joint was almost ready to come out.
Also some of the cheaper ones do not last as long, I tried one and also 02CDKJ we both ran them about 15000 miles before they were toast

randrson · Aug 10, 2011

I gotta agree, there.
I got a new crown UCA,and its now doing the exact same thing, at only about 15,000 miles. I'd really have to say that this is one part that you may want to stick with OE, unless Moog or Dana has the ball joint to fit it.

streetglideok · Aug 11, 2011

randrson said:
I'd still take a look at the upper ball joint on the tri-link. My 05 had on 76k when I bought it, the the ball joint was toast.

with it sitting on the ground, if you pry up carefully on the upper tri-link arm avoiding the brake line, you can see how much play is in the ball joint. there is a bit of rubber that isolates the ball joint center from the portion pressed into the arm, and when this rots away, it will thump on hard acceleration. \

A quick and dirty way to figure out if it the culprit is to put it in neutral on a slight incline and coast backwards, then pull the parking brake. If you get a good thump, that's the axle wrapping and banging the ball joint against the outer housing. (It was harder to tell that was my problem initially since mine is stick, and I had driven stick on almost four years.) if you find this is the problem, I got the complete new upper arm from autopartswarehouse.com for $130. It is from Crown, is made domestically, and aside from not having the Chrysler ID stamping, is exactly identical down to where the welds are located. I put it in last week and it made a huge difference.

Just what this guy said. May need to take it to a shop with a drive on lift. The suspension needs to remain loaded on a surface, aka on the ground to check the balljoint in back. Its well known on chrysler vehicles to go bad, making popping noises. Its a joint you dont want to break.

rockymountain · Aug 11, 2011

ok so further resurrecting this thread I think a person who lives in Spain replaced the balljoint years ago on his own. So would this work if you could get someone to press it in for you?

http://www.rockauto.com/catalog/moreinfo.php?pk=3249855

Would also want to replace bushings also on the two ends that go to the body. Can't determine if rockauto has those or not. I've seen them somewhere.

I'm thinking of getting the shop I go to to squeeze the balljoint out and put one in the next time I go in. I think it would still be cheaper than getting a whole new one as long as they give me a good rate on labor, which they usually do. Shouldn't take long with the right equipment which they have.

rockymountain · Aug 11, 2011

Ha! everything you would need is right here:

http://www.jeep4x4center.com/jeep-steering-parts/liberty-kj.htm

RedKJ04 · Aug 17, 2011

rockymountain said:
Ha! everything you would need is right here:

http://www.jeep4x4center.com/jeep-steering-parts/liberty-kj.htm

This is where I got the parts for mine! Great prices and super fast shipping!

Bulli · Aug 18, 2011

Have you checked out the mounting on the transfer case? The cross member holding the mounting that holds the transmission hides the mounting so check carefully. Mine did the same thing and after replacing all the ball joints and bushings on the rear I started going mad.
by accident noticed the mounting collapsed, replaced it and the thump was gone.

2004 KJ Rear End Thump

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