Mystery front end clunk - no it's not TRE's.

98 XJ, wj knuckles, 1 ton x-over, RC long arms
Been chasing a clunk in the front end on/off for years unsuccessfully.

Everything in the front end has been replaced several times over the years. Problem remains. All the TRE's are solid, steering box tight, track bar tight, new SKF unis just installed, new calipers/rotors. Lower CA joints have both been disassembled many times and always look good. Uppers I haven't actually pulled apart, but they feel very tight.

Driving over hard bumps at any speed results in horrible clunk (happens on every speed bump). Occurs while wheeling as well, but only on really choppy stuff. Doesn't clunk on anything big, or anything very small. It's just speed bump sized stuff that kills me.
For years, I've noticed that it doesn't happen nearly as often, or is muffled, when wheeling down a steep incline, but only recently realized that it's because I'm on the brakes. Any time I'm on the brakes, the clunk is gone, or very muted, which makes me suspect the upper CA joints are blown internally, or maybe something real silly like the front/axle side bolts aren't large enough diameter and the axle is rolling. Never notice anything suspect on video. Had a camera under the Jeep several times and never see anything.

I'm about to go lay in the mud/rain soaked driveway to pull apart my front end for the 30th time or so. Anyone have a brilliant answer to save me some time?

Check the joints in the arms?

well have you had anyone turn the wheel as you watch the front and look for slack? maybe start looking for fresh metal rubbing/striking marks. check the bumpstops also, check oil pan, possibly the track bar is hitting it. how far does the frame side track mount hang? might be hitting the coil spring pad

Did so a few minutes ago. They're solid. Even took them all apart for inspection. I'm still at a loss.

Demonoid369 said:

well have you had anyone turn the wheel as you watch the front and look for slack? maybe start looking for fresh metal rubbing/striking marks. check the bumpstops also, check oil pan, possibly the track bar is hitting it. how far does the frame side track mount hang? might be hitting the coil spring pad

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Don't this a hundred times. My front end is the tightest front end you'll ever find, as I've been trying to figure this out for years. There is zero play in anything as far as I can tell. I diagnose this shit easily for everyone else's Rigs, but can't find it on my own

And its not the coils hitting. That does happen, but only on serious compression, and it sounds obviously like a spring. This problem sounds like something shifting and clunking. I'm almost convinced at this point that it's not steering or suspension. I've gone through EVERYTHING a hundred times. It sounds like my motor is just bouncing off the frame or i've got a big wrench somewhere under the hood bouncing around. BUT, I've also swapped a V8 in since, and it's still doing it . I really expect it'll end up being a chunk of metal bouncing around inside the frame rail or something (except that I've also had all the rails opened up and never found anything).

The strange part is that when the brakes are engaged, the noise goes away and Jeepy sounds like a brand new vehicle. It's the quietest biggest Jeep I've ever ridden in, except for this one clunk.

I have encountered something similar in diagnosing may XJ's over the years. I have repeatedly found egged out holes in the control arm mounting brackets. No matter how tight you get things, the bolt shifts within the wallowed out holes.

Try putting a thick coat of paint over the nuts and bolt heads. Let it dry. Go out and make it do the same noise. Then go back and look real close at each one. I bet you will see that the paint has been broken.

I would guess it's the calipers shifting on the mounting bolts, or the pads shifting in the calipers. I had that problem and it was amazing loud for such a small movement.

old_man said:

I have encountered something similar in diagnosing may XJ's over the years. I have repeatedly found egged out holes in the control arm mounting brackets. No matter how tight you get things, the bolt shifts within the wallowed out holes.

Try putting a thick coat of paint over the nuts and bolt heads. Let it dry. Go out and make it do the same noise. Then go back and look real close at each one. I bet you will see that the paint has been broken.

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I've found the same in tonnes of Jeep, but unfortunately it's not the case with mine. All mounts are 3/8" thick steel. Pulled the bolts lots of times to double check. Bolts barely fit through the mount holes.

x-jay vision said:

I would guess it's the calipers shifting on the mounting bolts, or the pads shifting in the calipers. I had that problem and it was amazing loud for such a small movement.

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I've hoped it was that many times, but the way the Akebono WJ calipers go together, there is no way for them to shift around. You can beat on them with a Jeep hammer and they won't budge.
Keep the idea's coming.

Just an Idea, Wheel Bearing? when you apply the brakes they take some of the loading of the Bearings eliminating the noise.

Brand new SKF bearings. Made no difference swapping them. Everything in the front end is brand new, and has been replaced several times over the past few years that this clunk has been here. It's survived a complete suspension swap, engine swap, frame/uni stiffening/bracing.

Front Drive shaft?

Brand new. I do have a very slightly loose pinion on the front. That's sorta next on my list. Just been avoiding it as I'm sure it'll need a new bearing, in which case I gotta do another setup. Just time consuming.

Did you ever get your track bar sorted out? I remember you having issues with that.

The upper or lower control arms would be my guess. Make sure the bolts are actually putting enough tension on the joints. I've had to shim joints before because the gusseting of the mounts prevented the bolt from putting enough tension on the joint itself. It would be tight enough not to move by hand but not enough tension to keep it from popping under load.

Yea, track bar I built a 2" poly bushing and threw on a new heim on the other side. I thought so many times that it was the source of the clunk, but ... nope.
Control arm bolts are VERY tight. I stripped a 5/8" today just to make sure I knew they were going to be tight enough . Control arms are always my first suspect, and I fix so many goddamn peoples clunks after they insisted everything was tight (and it wasn't), so I'm PROBABLY not going to be that guy, but ya never know I suppose. I'll try to get it on video/audio. Maybe that'll shed some light.

I had a similar clunk...turns out it was driverside motor mount it was totally seperated from rubber,and the passenger side was good..i thought it was control arms or exhaust manifold or even calipers...but it was motor mounts...put some brown dogs in and no more clunk

Motor mounts was my original suspect years ago when I first got the Jeep. Replaced them with some MORE Bomb Proof mounts. Didn't help. Like seriously, I've had this issue since the day I bought this Jeep, and through years of wheeling and fabbing, it's the only problem remaining. I may have solved several problems that created the exact same sound, or maybe I didn't. It's not even a big deal as I know nothing is falling apart. Just losing my mind over the mystery, and it makes me ****ing crazy that my Jeep is otherwise ninja stealth. The V8 is barely audible at idle (much quieter than the 4.0L), there are no squeaks despite folding the uni in half in several directions (subsequently repaired, braced, and plated). It's strange watching wheeling videos of it because it sounds like I've stalled out every time I let off the gas, and when I idle by up the rocks, it's like someone hit mute. The clunk is the bane of my existence.

my shot in the dark guess would be shocks or springs. what do your spring isolators look like? what do your bumps look like.

are you sure its in the front end? check your trans mount, your rear bushings your exhaust hangars, etc.

Spring isolators are something I've never looked into. It's something I know nothing about. What are they SUPPOSED to look like? How can they clunk?
Shocks are all new and all on beef fabricated mounts. Definitely no play there. Bump stops aren't anywhere near being engaged when I hear the clunk. We're talking about bumps from 1/4" to 1.5". Any larger or smaller and the clunk doesn't seem to occur.
Trans mount is 3/8 steel with a 6" long, 1.5" thick poly bushing, also almost brand new, and it's been replaced and upgraded at least twice in the past few years (I just swapped the V8 in the past year, so I'm running a 4l65e/231c/j/241 case with a trans mount big enough to support 1000hp .

Coil isolators are really the only thing I've never looked at, but I don't really see how they can cause a clunk.