BoulderXJ

Installed a set of JKS lower control arms last year. Recently started getting a really bad clunk at the drivers footwell when hitting potholes or backing up then hitting the brakes. Then I started getting mild death wobble. I knew that my front upper control arm bushings were shot so I had a shop replace those. They tried to diagnoise the clunk and think that my JKS adjustable arm is giong bad. They drove it back and forth on the rack and the guy underneath thinks he felt the arm shift at the adjustable joint in his hand. (Yea, kind of a crazy thing to do..) They added a bunch of grease to the arm and the clunk got a lot quieter. JKS says that there is NO WAY that their arm could go bad, it is always the control arm bolts being loose, never the arm. I can guarantee the bolts are not loose, I tried to pull the arm this weekend and used a 5' breaker bar on the bolts, after flexing the breaker bar 2' to the floor I gave up, I didn't have time to get the Jeep up on jack stands to give myself more working room underneath, but the darn bolts are TIGHT, I'd guess way above the 135 ft-lb torque spec.

Drives much better with the new busings and the clunk is quieter (effect of new bushings or added grease in control arm...) but still get mild death wobble.

Anyone had any problems with JKS arms? I'm planning on pulling the arm this weekend and probably completely disassembling to clean out the grease and then check for slop in the arm. Thoughts?

xjmarc

Check the rubber bushings in the arms.

madmike283

My brand new RC lower arm was doing the same thing on Sunday while running Kelly Flats, the day after we installed them. Mine ended up being that the jam nut came loose allowing the slightest bit of play between the threaded inner arm and the outter DOM tubing. Make sure that the jam nut is tight.

BoulderXJ

madmike283: The JKS arms don't have jam nuts, they are supposed to be able to rotate. Take a look at: http://store.jksmfg.com/merchant2/me...de=Coil_Spring

xjmarc: Since the arms are only 1.5 years old I have a hard time believing that the bushings are worn out, I haven't worked them that hard. I'll check though.

OHHNOES

Might be a dumb question but have you checked your motor mounts? I say that because if the motor mount is bad it will feel like it is coming from the control arm. Mine did anyway. Good luck

BoulderXJ

So I think I've eliminated the control arm as the problem. I created a little tool to look for a shift in the control arm, and didn't see anything at all. I checked the control arm joints and the bolted joints at each end. Didn't look like anything moved at all. I just can't find this clunk. After driving it for a few days the clunk is definitely just as loud as ever. Headed back to the shop this week to see if they can find it. I'm out of ideas...

Here's a picture of my "tool". I took an 8" long piece of wooden molding and drilled a hole in the end of it, then stuck a pencil through the hole and taped it in place. You then take this and tape it to something that might be moving, say the control arm, and then put a piece of tape on something stationary like the arm mount. I used masking tape, you probably need to wipe down the surface first to get the grime off for the tape to stick. Look for the pencil drawing on the tape to indicate somethingis moving. Since my clunk happens by just putting it in reverse, starting to roll backwards and hitting the brakes, that's all I did, but I'd imagine that you could drive around a little like this. Hope this idea is useful for someone else.

gpXJ

You check your track bar upper mount? Mine was lose and I got this clunk right under my foot on the driver's side floorboard. Usually when putting it in reverse. I could hear it if I had the window down and radio off, as well.

BoulderXJ

gpXJ: Yes, I have checked it, but maybe I didn't check the right thing. I checked the bolts from the black bracket into the frame, and I checked the bolt that holds the rod end joint to the bracket. All seem good and tight. The one thing that I did notice is that the rod end joint seems slightly crooked (adjustable track bar, but the rod end joint wasn't turned for optimum travel). I thougth it might be bottoming out, but I looked at it really carefully and based on the where it is shiny it doesn't appear to be bottoming out at all.

Thanks for letting me know that caused a similar problem, I'll do an other check tomorrow.

xjmarc

Have you checked your drive shaft u-joints. If they get worn you will get a clunk and sometimes a jarring feeling when you put it in gear. Pinion bearing will do this as well.

BoulderXJ

XJmarc: I haven't been into the U joints, but I don't get the clunk putting it in gear, just when I hit the brakes when going backwards. Doesn't even have to be in gear for that, if I roll backwards on an incline and hit the brakes it does it. Also on flat ground it will clunk back and forth as the suspension rocks forward and back. Since the wheels aren't turning at that point it doesnt seem like a U joint. Never does it when going forward.

BoulderXJ

I swapped lower control arms out and the clunk is gone when backing up and hitting the brakes. Put the JKS control arms back in and the clunk is still gone. WTF? Vibration still there at 55 MPH. BTW - none of this effected the clunk I get when hitting bumps, still perplexed on that one.

I know it sounds like the bolts were loose, they definitely were NOT loose, but maybe something wasn't seating correctly. Too wierd.

I also spent some time dialing in my caster. It was pretty far out at 9 degrees. I shortened the LCAs 1/2" and lengthened the UCAs 1/2" and am now at 6 degrees. The vibes at 55 MPH have gone down a little since the caster adjustment, maybe.

SBG

I joined this site because my JKS UPPER arm IS lose at the point of rotation. JKS is full of **** if they say it CAN'T go bad there. It's a mechanical devices which rotates, and since it's mechanical, it CAN and WILL go bad. I think they should at least be honest, because the way the arm is constructed, it would seem that they would make replacable bushings behind the C clip. So, don't take JKS's word for it. Remove the arm, and check for yourself.

I have been having the same symptoms. Thought it was the trackbar, bought a Currie HEAVY duty. It helped a lot, however, it wasn't till I decided to start replacing my 5 year old JKS clevite bushings that I noticed the issue. I normally grab the arms and look for play, but it wasn't till I removed the passenger lower that the upper showed it's weakness.

Thought it was the bushings, but nope, right where the rotation is is where it was moving up and down. Now, do I ask JKS for replacement internals, buy a new arm, or buy Currie with Johnny joints?

BoulderXJ

SBG:
So in the end my problem was definitely not in the control arms. I spent a while on the phone with JKS and they were helpful but definitely skeptical about wear on the control arms. Basically they said that lots of folks blame their control arms and they used to get them shipped back to repair and never found anything wrong with them, so they would ship them back and the problem would magically go away. Got a bit frustraing for them. Anyway, after convincing them that I wasn't a complete idiot they were willing to ship me a set of new arms to try to see if that got rid of the problem. In the end I did some more troubleshooting and that wasn't my problem, see my posts above.


BTW - fixed the vibes by ... balancing the tires again. I'd recently had them balanced and hadn't lost any wheel weights, but they were out of balance again.


The clunk from hitting bumps was from bad shock mounts. The previous owner did really poor work and totally jurry rigged the shock installation. Fixed the front shock mounts and that clunk is gone.


After all those fixes the jeep drives awesome, I'm really pleased.


I ended up convinced that the JKS arms are really tough. I spent a lot of time talking about design details with them and was impressed. As you say, there are moving parts, it is possible for them to wear out, but they are pretty darn robust and the guys at JKS just haven't seen it.

The smaller shaft rides on a bronze bushing pressed into the larger shaft. They match machine the ID of the bronze bushing for each control arm and control tolernaces very well (I feel like I shouldn't quote the exact numbers, but as an aerospace engineer I can say that they know what they are doing). Additionally they maintain really good thread engagement on very tight tolerance threads even at max extension. The threads are cut directly into the arms. Basically there are only 3 pieces, the two pieces of the arms and the bronze bushing.

I'm sure that it is possible that you could have worn out that bronze bushing and torn up the threads to where there is play in the arm, but if so you are either working that jeep really hard off road, or there is something else in your suspension that is way overloading the upper control arms to get that kind of wear.

Have you taken the arm off yet to evaluate the play, or are you doing it still installed? You might feel something very different if you completely remove the arm.


There aren't any pieces inside the arm that can be replaced, but if you really have a bunch of play in the control arm I'd work with the guys at JKS, talk to Jim Nollette. I'm sure he can help you out. Good luck!

brian0128

I have this exact same problem with my Jeep. The problem is identical. I hear it when hitting bumps, backing up and hitting the brakes or even going around a left turn and unloading the driver's side wheel and hitting bumps.

I started getting the clunk right after I put on my OME lift. I've got OME springs, shocks, JKS Lower Control arms and JKS trackbar. Trying to track down this sound I've replaced my ball joints, hubs, bought new JKS upper control arms, and even swapped my lower control arms side to side trying to find it. Torque has been checked on everything including the trackbar at both ends and the mounts.

I tried disconnecting my JKS disconnects and also drove without the front driveshaft to rule out those possible issues.

The other day I decided to put the Jeep on a lift and hit the surface of the tire with a 3lb sledge. If I hit the tire I could hear a clunk on the driver's side. It's crazy, but the sound seems to be coming from the caliper area. It's almost like the pads or caliper are moving around but I checked all the bolts and they are tight.

Anyone have any ideas?