Frame cracks in rear

lynn · Oct 18, 2004

About halfway to the Tioga campout, we stopped for gas. My buddy following me said something didn't look right. We looked under, saw on the driver's side a big crack on the frame just along the shackle hanger. On the passenger side, the same crack, but bad enough that the shackle hanger mount has pivoted upward in the front, into the frame channel. Essentially the shackle hanger on the passenger side appears to have broken free of the frame, or nearly so, the front of the shackle hanger is pointed up to the top of the frame rain at about a 45* angle, and of course the rear portion is angled down below the bottom of the frame rail. This in turn changes the position of the shackle, but still allows the Jeep to drive and track straight.
With the weight on the spring, it didn't give me any problems for highway driving, so I drove it the rest of the way to camp and got set up. I left the Jeep sit for the weekend, the only offroading I did was as a passenger in a '04 Rubicon (what an awesome Jeep!! Comfortable too!!)

I discussed the needed repair with a bunch of the guys there, who have more fab experience than me. The recommended fix is to first drop the fuel tank. Then I'll have to remove the rear bumper/tire carrier.
Next,remove the shackle hangers, then drill out the ends of the cracks, clean them with a grinder, weld them up, grind them smooth. Next, either fabricate U-shaped pieces of appropriate length, or cut the top off of some square tube, and slip the U over the C channel, welding the U to the top rail of the frame, essentially boxing the open channel. Then weld and bolt the shackle hangers back in place, as well as drilling out holes for the bumper brackets.

This approach sounds reasonable to me. I gave some thought to doing this job up there at a buddy's Dad's place nearby, but I decided to wait and do it at home.

What do you think of this aproach? Other ideas, recommendations, things to keep in mind?

My wife suggested we sell the CJ as well as her ZJ and just get a new Rubicon...

DanStew · Oct 18, 2004

Welcome to the wonderful world of the frame crack, i almost had that same problem but i caught it just befoe it could do that. I am eventually gonna do that, i ended up just welding up th ecracks and let it be, i know they will come back, but eventually i will either sleeve it or maybe just get a new frame alltogether. The tube over the frame is a very good idea, but i am not sure there is tubing the size just over the frame width. Hope you get it figured out!!

Project71-5 · Oct 18, 2004

Lynn, it sounds like you have more damage than just a frame crack that can be welded up. Is the frame rusted through, which in turn caused the shackle hanger to break free and rotate up?

I think the u-channel over the frame is the best option other than cutting the rear portion of the frame totally off and then fabricating a new one.

plunkinberry · Oct 18, 2004

As much as I'd love a new Rubicon, you seem to have a lot of personal investment in yours... so I think I'd pass on the Rub...

James P. Enderwies · Oct 18, 2004

Lynn: In talking to Gerry, a local hot rod builder and restorer, he sugested the following procedure that he uses.

First drill out the end of the crack like you mentioned and weld it up.
Second, weld a piece of "strap iron" of the approiate thickness in the INSIDE of the C channel. Welding lengthwise on the inside of the channel and on the outside edge. Do not weld across the frame.

This should be sufficent. But at the shackle mounts, you might want to box it. You can then weld a piece of steel across the inside edges of the channel at the shackles. If you weld on the outside of the frame at all, make sure that the steel is in the shape of a parallelogram and weld on the top and bottom edges only and not across the frame.

Ledge · Oct 18, 2004

James P. Enderwies said:

First drill out the end of the crack like you mentioned and weld it up.
Second, weld a piece of "strap iron" of the approiate thickness in the INSIDE of the C channel. Welding lengthwise on the inside of the channel and on the outside edge. Do not weld across the frame.
Click to expand...

Can you clarify this a little more? I'm a little confused. Excuse my picture below, but is this what you mean? Drill and weld up your crack, and then, assuming the picture is of an inside view of the frame, put a piece of strap over the welded crack?

_________________________

weld
| s |
| t |
| r |
| a |
| p |
weld
_________________________

James P. Enderwies · Oct 18, 2004

Ledge: Your diagram is what the outside would look like if you welded a plate there. But it should be "pushed over" so to speak to form a parallelogram.

On the inside strap, the best way to describe it is to take your hand and form a C with your fingers and thumb. This would be a cross section of your frame. Now where your thumb is on the bottom, lay 2-3 fingers of ther other hand across your thumb. You would then weld where your fingers touch your palm and where your fingers touch the tip of your thumb. These welds would be parallel with the frame and not across it. This strap would bridge the crack.

67cj5 · Oct 19, 2004

As an aviation welder who has done quite alot of fabrication in heavy equiptment as well.My recommendation would be.. Stop drill the crack, make sure the drill bit diameter is large enough to drill out the end of the crack as well as any unseen cracking beneth the surface. Assuming there is no substantial rust. You then weld the crack down the sides. After this you grind the existing weld flush and using flat steel make a fish plate for both sides. the plate should extend at least 4 inches on both sides of the crack and be the same shape as the frams rail sides. Drill a 1/2 inch ho;e on both ends. Weld the plate on and then plug weld the holes to the origional frame. Using channel to lap over the frame is not a bad ideal, but the strength of a repair like this comes from flat steel running lengthwise with welds to the existing rail. If you need moreinfo. on this kind of repair email me directly and I will call you and offer any help I can.

lynn · Oct 19, 2004

Thanks for the input guys
Looks like I have a few options.
I'm not really going to get a Rubi. And a new aftermarket frame isn't in the plan right now.
This particular problem appears to be more the result of some incorrectly placed attachment welds than the result of exceeding the capability of a sound frame.
So I will carry on with a plan to fix the frame.

Can someone clarify the term "fish plates" ? I've heard this many times... I have an idea of what it means as far as shape but I'm not sure if I'm right. Can someone give a good explanation?

Jim, I understand your description of the strap. On one side, that should work, drilling out and finishing the welds as Chris described. However, on the other side, it's more than a crack. It appears that the lower portion of the C-channel where the shackle mount was riveted has broken free of the channel, so that's maybe a 2" piece. Removing the shackle mount then laying in a strap will result in only the strap bridging this 2" gap, then I'd have to bolt/weld the shackle hanger to the strap to get it back into original location. That doesn't sound good to me.

That's why I was thinking of using a piece of square tubing with one side removed to form a U, then slipped over the C. That would bridge the gap without putting any undue stress on the area where the section is missing. I'd weld along the top edge of each leg of the U, welding it to the top inner and outer edge of the C channel. With a tight slip fit the stress shouldn't be focused in any one area. The only welds would be along the top, parallel with the length of the frame, no welds 90* across the upper, lower or side of the C.
Chris, If I do it this way are you recommending that I also do a plug weld on each end of each U, to the side of the C? Like right here:
--> |[|
If my square tube was a foot long, would this plug weld be centered and about an inch in from each end?

Boy it's not easy describing this without pics or examples, is it

Again, thanks for your continued input!

blevisay · Oct 19, 2004

lynn · Oct 19, 2004

Oh YEAH!!! THAT"LL fix it!!! R) R) LOL!!! R) R)

blevisay · Oct 19, 2004

I was looking for a pic for you and couldn't help myself........

blevisay · Oct 19, 2004

timgr · Oct 19, 2004

I assume that this is a C-channel part of the frame, and not boxed.

A fishplate is applied to the outside vertical surface of the frame rail. Typically the longer the better, since that distributes the stress along a longer weld. The picture that billy posted shows a fishplate with a righ-angle bend, which would work well if the frame rail doesn't have any curvature up-and-down. An important point in both Jim's strapping method and in the fishplate drawing that Billy posted is not to weld across the frame rail. Only weld parallel to the long axis of the frame.

I've seen reinforcements with strapping, and with plates. Sometimes the ends of plates are cut into a V or fish-mouth, and the entire edge is welded. I don't know if this is more to increase the length of the weld across the frame rail, or to make the weld more parallel with the long axis (in tension along the weld instead of across) or both.

Re the question to Jim, I'd think that you'd weld the broken-out hanger back to the frame, then weld the strap in. Doing it the way you describe would require welds across the short axis of the plate, which would be bad. If you have to drill a hole in the middle of the strap to get it to fit over the attaching bolts/rivets, so be it. Just make the strap thicker to compensate.

Caveat - haven't actually done this stuff - only seen it done at the dealership.

hth

blevisay · Oct 19, 2004

The V is usually to add more welded area.........

blevisay · Oct 19, 2004

http://www.tpub.com/content/hummer/TM-9-2320-387-24-2/css/TM-9-2320-387-24-2_1221.htm

FWIW

blevisay · Oct 19, 2004

http://www.4x4wire.com/jeep/projects/pieces/frame2/

blevisay · Oct 19, 2004

http://www.jeeptech.com/body/frame.html

lynn · Oct 19, 2004

Billy, Tim, thanks for that additional input. Lots of good info to consider.

blevisay · Oct 19, 2004

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