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Discussion Starter #1
I was recently laying under my Jeep and looked up and noticed that my rear cross member at the 3-link cradle had cracked in the HAZ of the weld. Time for a double-triangulated 4-link!

Figured I'd share some pics of this failure as it's pretty scary. I'm really lucky I noticed this when I did as I was getting pretty close to losing my upper frame mount.

I will fully disclose that technically the only RK products here are the cradle and rod-ends, I made my own links in slightly different geometry than theirs. I also mounted a transfer case skid to the front cross member. None the less, I'm 99% sure this most if not all of this is caused by the 3-link.

I'm not bashing RK here as I honestly don't care, been wanting to strip this suspension out for a while anyways. I'm just posting this as a warning to inspect your 3-links frequently and be really careful. I beat on my vehicle extremely hard so maybe this wouldn't happen to everyone (60MPH through big dune whoops, small jumps, and trail wheeling faster than anyone I go out with).

Rear cross member where I first noticed the problem, this crack most likely started in the HAZ of the weld:



Upon removal and further investigation, it was found that this crack had propagated around about 300 degrees of the cross member and there was just an inch of metal still holding it together:



Moving along to the other cross member, I noticed that fatigue cracks had started to form but had not yet propagated quite as severely. In this location, the cracks are not in the HAZ of my weld:



And finally, during front cross member removal, I noticed that one frame side had cracks propagating from both sides on the top end, of course I hadn't welded in this location at all, and it is not forming in the HAZ of a factory weld, so this is just a structural deficiency:

 

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Wow. That is pretty insane. Haven't seen anything like that in 13 years. The cross member crack is nuts. What is with the rest of plasma/slag stuff on the sides where the cross members appear to be going to the frame. If anyone else has any experience like this we would love to see it.
 

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Soooo...is it safe to say you've been taking that thing off some sweet jumps? :drinking-42:
Hold my beer indeed. :lol:

Not laughin' at you, just a thought of potential causality.
 

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Are you saying you have seen another one or are you still talking about this one which is the first one we have ever seen. Not trying to dismiss it at all. It is worth looking into for sure but just trying to stick with facts and not spread rumors.
 

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The photo is from 2013. I removed the upper bracket after noticing the cracks in the frame. I am sure it was user error, or not installed right, or an RK product used with other manufacturers parts. You guys should have nothing to worry about, it's not your fault.
 

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The photo is from 2013. I removed the upper bracket after noticing the cracks in the frame. I am sure it was user error, or not installed right, or an RK product used with other manufacturers parts. You guys should have nothing to worry about, it's not your fault.
Is that what we said? Let's be clear!
 

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Discussion Starter #11 (Edited)
Wow. That is pretty insane. Haven't seen anything like that in 13 years. The cross member crack is nuts. What is with the rest of plasma/slag stuff on the sides where the cross members appear to be going to the frame. If anyone else has any experience like this we would love to see it.
This was just discovered a week ago for me, so anything from thedirtman is a second case.

The slag is because I was actively plasma cutting the cross member out when I took this pic. I cut the bottom half off, then the cracks became visible. There's no way to inspect the top without body removal so I hadn't even discovered those cracks until it was already being removed. Fortunately, the cracks made removing the rest quick and easy!

Edit: technically, it's not impossible to inspect the top without body removal, but you'd have to really try and probably wouldn't simply notice.
 

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You will like the double triangulated set up better. How high are you going to mount the frame uppers? Have your lower mount cross member designed yet?


It's something to think about, that upper bracket breaking loose at speed, the carnage would be impressive. Maybe RK should review their product liability coverage for those thousands of kits out there that have the potential to fail.

I had a currie tie rod fail on me and glad that didn't happen at speed but if I would have taken it out one more time it would have. Broke it in two with my hands. They didn't get the tube drilled in the center and it broke out where the threads bottomed out. They half ass replaced it for me.
 

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Discussion Starter #14
You will like the double triangulated set up better. How high are you going to mount the frame uppers? Have your lower mount cross member designed yet?
The frame uppers will be about at the middle of the frame rails, and the lowers about an inch below. That gets me around 4.25" of separation at the frame, which isn't fantastic but not too bad. It comes out to an anti-squat in the high 70's, I'd rather be a bit closer to the 60's or low 70's but I think it'll be good enough.

What's really the problem for me on the uppers is the body reinforcement rails highlighted in red below. In order for the uppers to clear those during full stuff (where the upper axle link mounts are right up to the tub), the frame side has to be no higher than the middle of the frame rail. If you know any good tricks to get them higher while keeping the body panels intact, I'd be interested to hear. I assume I shouldn't just go cutting those reinforcement rails out of the body without beefing it up on the inside, which I don't want to do (spare sits on the floor and slides right under my rear strut bar, no room for the tire to be higher).



Lowers will mount onto a structure much like what I had before, except it will be strong, and made of 2x3 1/4 wall instead of mounting onto the factory crossmember which has been removed.

 

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I removed those tub supports (before I cut the entire rear off and tubed it). You could add a body lift to get some more clearance. When you are planning out the new cross member make sure you plan for the exhaust routing.
Last cross member for a double triangulated on a JKU was made from a piece of 3"x8" tube. I boxed out the area for the driveshaft and recessed the lower mounts into the tube. I don't seem to have a photo of it. Next time he is here I will shoot some photos.
 

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For once in our lifetime we owe dirtman an apology for missing his post back in 2012. No, we have never seen this before (truth). We take all things seriously. Out of the 4000 plus long arm kits we ship a year for the JK these are the only two we have seen. Does it make sense? Nope. If one of the cross members was to show signs of fatigue cracking, it should be the front one the cross link is attached to. The bending and forming is under much higher stresses naturally and the arm attaches much closer to the front member, than the rearward member.

You have all seen many many long arm mount failures out there and we feel very comfortable saying RK is among the very least. All mounts have the potential to fatigue and fail at some point. That is why race car chassis go in the garbage after 3-5 seasons. They are done and beyond the point of repair.

Is it possible that someone or two have piss pounded their JK for longer and harder than we have or anyone else, sure, anything is possible.

If there are pre-existing stresses in the mount from being formed or material being stretched by the factory or even if someone welds improperly and cuts deep into the base metal causing extra stress the below will be available to everyone as soon as our suppliers come back up to speed after this corona virus stuff is all behind us. The part number will be RK07764. It will be free to anyone that has a stress crack and we will post it as available publicly on all social channels. This is something we take serious! This bracket will gusset the material where the aforementioned fatigue cracks are show ensuring no failure would be possible. One on each side of the cross member will be the suggestion.

The JK long arm lineup was refreshed this year to match what we did on the JL applications. We feel so extremely comfortable with this mounting system that the rear upper components carried forward with all the new stuff. I would not call 2 out of 13 years a shit storm.
But again, it is something we take serious here.

At RK we could never put someone on payroll who thinks rubber to steel is a good bearing surface. That person would fail the ienginerring interviewing process right away. Rubber is a high coefficient of friction material. To use it on a steel surface for a bearing is not a good idea.

To this very second at RK we feel the independent 3 link with a track bar is still the best suspension design for JK and JL owners looking for the ultimate in bind free suspension movement not wanting to replace their gas tanks. Keep in mind, DOT law states all gas tanks must be located between the axles for any vehicle to be DOT approved as of Jan 1 2007! You can thank the Crown Vic for that.
 

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If you look close, those tub stiffeners seem to line up with where seat/seat belt mounts are. That's really the only reason I could see for them.

I cut through them for my upper links, just filled in the open ends.

Here's a shot of what your dealing with:

DSC08778.JPG
 

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For once in our lifetime we owe dirtman an apology for missing his post back in 2012. No, we have never seen this before (truth). We take all things seriously. Out of the 4000 plus long arm kits we ship a year for the JK these are the only two we have seen. Does it make sense? Nope. If one of the cross members was to show signs of fatigue cracking, it should be the front one the cross link is attached to. The bending and forming is under much higher stresses naturally and the arm attaches much closer to the front member, than the rearward member.

You have all seen many many long arm mount failures out there and we feel very comfortable saying RK is among the very least. All mounts have the potential to fatigue and fail at some point. That is why race car chassis go in the garbage after 3-5 seasons. They are done and beyond the point of repair.

Is it possible that someone or two have piss pounded their JK for longer and harder than we have or anyone else, sure, anything is possible.

If there are pre-existing stresses in the mount from being formed or material being stretched by the factory or even if someone welds improperly and cuts deep into the base metal causing extra stress the below will be available to everyone as soon as our suppliers come back up to speed after this corona virus stuff is all behind us. The part number will be RK07764. It will be free to anyone that has a stress crack and we will post it as available publicly on all social channels. This is something we take serious! This bracket will gusset the material where the aforementioned fatigue cracks are show ensuring no failure would be possible. One on each side of the cross member will be the suggestion.

The JK long arm lineup was refreshed this year to match what we did on the JL applications. We feel so extremely comfortable with this mounting system that the rear upper components carried forward with all the new stuff. I would not call 2 out of 13 years a shit storm.
But again, it is something we take serious here.

At RK we could never put someone on payroll who thinks rubber to steel is a good bearing surface. That person would fail the ienginerring interviewing process right away. Rubber is a high coefficient of friction material. To use it on a steel surface for a bearing is not a good idea.

To this very second at RK we feel the independent 3 link with a track bar is still the best suspension design for JK and JL owners looking for the ultimate in bind free suspension movement not wanting to replace their gas tanks. Keep in mind, DOT law states all gas tanks must be located between the axles for any vehicle to be DOT approved as of Jan 1 2007! You can thank the Crown Vic for that.

Looks like a half assed bandaid fix, put it out there and see if it works. I would expect a redesigned wrap around bracket is in the works? Noticed nothing on your website or instagram about maybe checking that mount for cracks, I doubt a lot of RK users are just going to stumble onto this thread.
 

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You are a fucking douchebag. Give it up. Dirt only points out how shitty your products are. You provide the proof every time you post.
Dirtman did not respond to it because that was not the response. It is pretty easy to say what you want to say on forums with no recourse. But hey, guess you are pretty hard core calling us a fucking douchebag. My feelings are hurt!
 
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