cracks in unibody

[TigerXJ]

Hey guys, I'm an alum, joined the club shortly after it formed when I was a sophomore. Anyhow, after a brief 4-year exhile in Chapel Hill for med school, I'm back in Anderson working at the Family Medicine Residency.

I've had a bumper built by Brooks on my jeep for about 5 years now. It was a great bumper for the tire carrier and as a recovery point. However, it was not great as a tow point because it was too high and too much leverage, especially when you account for the 7.5" drop hitch I had to use to tow any trailers. Well, after my move towing my trailer, I started to get concerned about the stock bumper mounts (the bumper used the stock ones and the hitch mounts), especially after towing my dad's boat one weekend. I found cracks around the stock bumper mounts, so I pulled the bumper, and found this:

on the passenger side


on the driver's side


on the rear




And several more like that above. Basically hairline cracks spreading from the mounting points. This came from heavy tongue loads with a lot of leverage on a long and high hitch point, that caused a lot of torque on those mounts. The flat bar that tied into the hitch points was great for straight on pulls, but not for weight on the hitch, and didnt resist the torque.

The cracks didn't stop at the mounts. The first set of pictures are looking back at the rear crossmember. The rails basically split where they meet the rear crossmember.

I have since stop-drilled the cracks so they wont spread further. On the inside, I cut the remainder of the rail that welds to the rear crossmember and removed it since it was already weakened. My plan was to get angle or flat plate (welded into angle) to tie the framerails back into the rear crossmember. This would overlap the mounting holes, which I would drill out and add nuts for the mounting bolts.

The problem is I don't weld.

I am looking for ideas to repair this before my new Rigid rear bumper gets here, and how to make it strong enough so I don't have to worry about it again. Also trying to find someone who has a little experience welding thicker metal to sheet metal. I'm willing to grease a few hands, booze or cash or both, take your pick.

So, how should I fix this crap?

kenny

Oh, and a gratuitious jeep shot. If you see me around clemson, wave. We drive it to the games to tailgate:

 

[97TJGUZZY]

Hey kenny, hate to hear that the bumper didnt work as planned, its hard to make something high clearance that can still tow a ski boat.... well actually i guess the bumper held but the unibody wasnt up to the task. To fix this I would do the cutout for 2x3 box steel that goes inside the unibody rails. I'll see if I can find the write-up I read on naxja. There were people have trouble with the same cracks you are describing from other bumpers and they fixed it with the frame sleeve.

 

[Steve97tj]

David or Ronnie could help you for sure as they both have welders up here in Clemson and Ron just did some repair on his unibody so i'm sure he could help you with advice too. I understand metal/welding but none of that unibody crap.

Hijack: Just wondering what doctors/practice your working with? My dad did his residency there years ago. He's a family prac. in Abbeville now, bout an hour away.

 

[TigerXJ]

AnMed Family medicine residency.

Brooks, the bumper was fine, the unibody wasn't up to the task. In fact I sold the bumper to a guy on Naxja with full disclosure. Angle instead of flat plate for the frame tie-ins probably would have done it, but hindsight is 20/20. I have seen the naxja thread with the 2x3 box slid into the rails, but I already have a rigid rear bumper being built, and since I can't fab, it limits my ability to design my own mounts/bumper. Even if I did that, I'd still have to tie the rails back to the rear bulkhead, which will require some patching of that joint. Also, when tht part cracked, I lost the two inside stock mounts on both sides. Thus I still neeed to add material to have something to bolt to.

 

[TigerXJ]

Steve what are ron's and david's names on here?

 

[Steve97tj]

clemson5.9zj is ron and david d i think is davids.

 

[David D]

Yup that's me. Anyone have a link to the write up that brooks is talking about? To repair the cracks you currently have would be a ton of work. You basically have to drill a hole at the end of all the cracks, grind a bevel, weld them up, and then grind the weld smooth. I would probably be easier to just replace it with the box tubing.

 

[David D]

This what you were talking about brooks?

http://www.naxja.org/forum/showthread.php?t=993533

 

[Ghost]

This what you were talking about brooks?

http://www.naxja.org/forum/showthread.php?t=993533

You might could cap the 2x4 with .25 plate and weld nuts to the back where the 4 holes are on each side. Then drill out the old nutserts big enough for the new nuts to sit in recessed. Then rosette weld the tube to the unibody frame rail and fully weld the plate to the back cross member.

 

[TigerXJ]

So apparently Joe Meaders lives 15 minutes from me in Anderson. I took it by his place last night and we looked at it together. At this point, our plan is to bevel out the cracks so that when we weld them up and grind flat, there will still be actual weld there.

We are gonna use some angle stock, like 1/8" on the inside framerails (fuel tank side) and stitch/spot weld them on to tie the framerail back into the rear cross member. We will then drill them out and weld on the nuts for the bumper mount.

The rigid rear bumper mounts use the stock mounting points (and the hitch points). We gonna try to copy the NAXJA thread, and cut open the access point in the rear of the framerail, insert 2x4 tube with nutserts. That will be welded to the back of the rigid mount that uses the stock bumper mounts. That will give a sandwich of the framerail, with two mounts that have a strong vertical component that will resist deflection from towing that caused the demise of my last bumper.

Don't know if I can explain it any better than that, but in short, we will try to do the NAXJA thing to further beef up the already beefy rigid mounting system.

Below is a link to the pictures from Terry at rigid for basically all his products, but the rear bumper mounting system specifically.
http://www.flickr.com/photos/rigid/sets/72157601539411607/

when looking at the photos, take the part labeled "B" in the first photo, and weld the 2x4 tube to the back of that, and insert the 2x4 into the framerails with a nutsert welded inside just like the naxja thread posted above.

 

[97TJGUZZY]

sounds like a solid plan

 

[TigerXJ]

Here is the rigid subframe, with the 2x4 frame inserts bolted to it. The brackets on the floor will be welded to the 2x4

 

[TigerXJ]

Here is how the stock bumper mounts from rigid will be welded to the 2x4

 

[TigerXJ]

Here is the main subframe mounted. There is a bracket that makes use of the two center holes in the rear x-member


Had to enlarge those holes a bit to get everything to line up


Here are the subframe extensions that catch the 4th bolt on the unirail. Also the center mounting bracket


And lastly the main bumper body. Getting a couple coats of POR-15, and topcoated with rust oleum hammered that is on the rest of the jeep. I've had really good results with POR-15 on my rails and front bumper. Even when some of the rustoleum chips, the POR is still well adhered underneath.


Will get the brackets welded up by Joe Meaders sometime in december. I'll probably go ahead an mount it as is until then.

 

[TigerXJ]

I realized I never showed the new mount extensions. This is the driver side with a cutout for the fuel filler hose


Here is inside the driver frame rail. You can see the cutout in the rail for the hoses. That's the old nutstrip brooks made for the old bumper. You can also see the shackle bolt that I trimmed down by about 3/4"


And here is the pass rail with the 2x4 box tube in place with the factory nutsert. I have replaced it with 2 JCR strips. I had to trim them down to fit inside the tube. The tube is 1/8" wall thickness.

 

[TigerXJ]

Here is the subframe extensions that catches the last hole in the frame/nutsert.


This is the center mount bracket bolted up. You can also see the bracket at the stock location that will eventually be welded to the box tube


Here is a shot underneath getting the bumper main body bolted on


Here is another nice touch. The bolt on the top left (silver) is an anti-rattle set screw for the hitch tube. I like it cus when I tow my utility trailer that bitch rattles like a couple monkeys with hammers inside a steel drum

 

[TigerXJ]

And an here is some more of the prep for the crack repair. Reporting from this thread, I found this under my jeep in August:

This is the rear bulkhead on the drivers side. The main rail is supposed to fold over onto the bulkhead and is spot welded there, with 10mm nuts welded on for the stock bumper mounts.

It will be patched/repaired with these:

They are from scrap left from the 2x4 box tube.

They will fit like this on the frame rail to bulkhead:

Hopefully it will eventually be welded to the unirails and the bulkhead. Those bolts are the replacements for the stock nuts I lost when it cracked.

 

[TigerXJ]

And finally here is the finished product:

There are 20 bolts holding the subframe to the uniframe, and an additional 2 holding each end cap to the body, with 5 holding each endcap to the bumper main body.

There are 9 grade 8 bolts holding the bumper main body to the jeep.

The nice thing is that the endcaps are modular, so when I have the cash and need for it, I can send them back and pay the difference for the swingout tire carrier endcap and swingarm for about $250 I believe. The bumper I have shipped bare metal was $590.


All that is left as above was to get the last bits welded for the cracks and for the tube to the bumper brackets. I may add frame tie-ins from the endcaps to the rail like AJ's offroad bumper

 

[Steve97tj]

That looks really good.

 

[TigerXJ]

I'm really happy with it. Can't wait to get the swingarm on it in a year or two when I step up tire size and I can afford it - baby on the way kinda takes the jeep money.