A crack in my frame

[SierraHawk]

Yikes... Just for the fun of it, contact a shop that repairs semi-truck and trailer frames. I've broken the frame on my travel trailer twice (two different locations). Did some research and found that the welders use three odd shaped pieces of steel to strengthen the primary weld. Drilling a hole at the end(s) of the crack seems to be a common practice. Its supposed to stop the crack from crawling any further. There was a place down the road that builds and repairs utility, horse, travel trailers, etc. I had them do the first repair as instructed. Its held for the past 10 years. To repair the second crack, I drilled a hole at the end of the crack and then bolted a 14" piece of heavy channel over the crack. Used Grade 8 bolts and turned a torque wrench loose on them. That was 6 months ago and it seems to be holding up.

[beaker]

I've been out for a while. I went down the pickup route while van prices went bonkers. Still have my E-350 though.


carringb has excellent advice about a deep groove and a full penetration weld. In my industry, we drill-stop cracks that we don't want to propagate, but if we have crack that we want to remove for good, we grind it out, and verify that the crack is fully removed with dye-penetrant testing (magnaflux is a common automotive PT brand) before attempting to weld-repair.


As an aside, an angle grinder is handy, but it puts a lot of heat into the weld and can cause it to run. A conical burr-bit on a die-grinder will vastly improve your odds of success.


Regarding the weld, the photo you posted shows rust on the inside of the indication. You may have better luck with 7018, assuming you have removed the rust. If you still have rust as shown, I would grind it out, or stick with 6011. One thing that might improve your success is preheating the surrounding metal prior to attempting a weld.

[Vanimal]

Many unibodies have these issues. Jeep XJ's forexample have frame stiffner kits. My 2cents after you do exactly what Carringb sugested plate the frame. Drill or cut holes in the plate and weld fill the holes in.. Commercial trucks get the frames cut all the time for bodies they either dbl the frame at the spot or fish plate it!

[TomsBeast]

I've have really good success with the above drill hole at the ends of the cracks, vee out the crack and weld, grind flush. Then add a patch, 'sister' or 'doubler plate' that extends a couple inches either side repaired crack, weld it in place.



If you think about it, your frame cracked because of a stress concentration (or maybe flaw in the formed tube, but we can't know that, so let's assume overstressed). Often a simple vee out and weld will just lead to another crack... I proved that with a Chevy Vega V8 conversion I build when I was 17, I chased all sorts of overstressed areas. Anyhow, the doubler plate helps reinforce the area of concentrated stress, and spread that load over a wider area. Often double plates are diamond shaped, as to not abruptly create a new line of stress concentration a couple inches away, rather, gradually introduce the force over a larger area. You can find examples of rectangular tube being sliced together with a butt joint, then the seam reinforced with a diamond shaped doubler plate on top of the seam.


skip to 8 minutes in:

https://www.youtube.com/watch?v=a17ghKf_-Kc

[Orv]

Originally Posted by SierraHawk

Drilling a hole at the end(s) of the crack seems to be a common practice. Its supposed to stop the crack from crawling any further.

Cracks propagate because stresses concentrate at the sharp tip of the crack. The idea of stop-drilling is when the crack reaches the hole, you have a nice round surface to spread out the stress. It's routine on aircraft for non-critical cracks, especially in things like wing fairings and engine cowlings that aren't structural. I used to fly sailplanes and they'd fix cracks in the plexiglass canopies by stop-drilling and sometimes gluing on a doubler.


Of course, if the stress is high enough, you miss the tip of the crack, or the hole is too small, the crack may keep going anyway.

[posplayr]

Originally Posted by Orv

Cracks propagate because stresses concentrate at the sharp tip of the crack. The idea of stop-drilling is when the crack reaches the hole, you have a nice round surface to spread out the stress. It's routine on aircraft for non-critical cracks, especially in things like wing fairings and engine cowlings that aren't structural. I used to fly sailplanes and they'd fix cracks in the plexiglass canopies by stop-drilling and sometimes gluing on a doubler.


Of course, if the stress is high enough, you miss the tip of the crack, or the hole is too small, the crack may keep going anyway.

I have drilled out the end of cracks as well but I have also had the crack propagate right through as well. I have a 1987 Klein mountain bike frame where the seat tube has an extension above the top tube and it flexes and causes a crack that drilling did not stop.

By the time you end up V grooving the crack to get good weld penetration, the drilling is pretty much irrelevant. Depending upon how much metal plate you backup the original frame with, again this drilling will have little if any effect especially since that drill hole will get welded up with a backing plate.

As many are echoing here the part is cracked because of overstresses and unlikely because of a manufacturing defect. Therefore the frame needs to be made stronger here else the crack will simply re appear.

[Lilnuts2]

Does anybody else consider the possibility that the frame cracked due to the leaf spring 4x4 modification to it? A modification the Van was not designed for from the factory .
I'm not exactly clear where the crack is on the frame. But it seems to me a leaf Spring with a moving rear shackle design puts more of an upward force on a frame where a trailing arm style like a coil Spring design puts more of a rearword pressure on the frame. Either 4z4 design puts more stress on the frame then the stock twin I-beam design. Just tossing this out there for conversation.

[arctictraveller]

The original crack was welded up using larger MIG wire to get better penetration, then primed and painted, but I'll keep a close watch on it just in case. Then, I found another crack, this time in the drivers side frame horn where the front bumper attaches. I'm guessing it could have something to do with a lot of overhanging weight with a heavy bumper and winch combination and / or some heavy winch stalling pulling on a tree stump I was pulling out of the ground. Anyway, it wasn't as big as the first one, it was in the factory welded on bumper attachment plate and I just ground it out and welded it. I'll keep an eye on it, but I'm sure it's fine. Both of these cracks were found by accident, but I do make an under body inspection after every trip, but from now on, I'll look a lot closer.

[QUOTE=Lilnuts2;310403]Does anybody else consider the possibility that the frame cracked due to the leaf spring 4x4 modification to it? A modification the Van was not designed for from the factory .[QUOTE]

I suppose that's possible, but there are plenty of leaf spring conversions out there and I haven't heard of any other cracked frame issues, but certainly something put a lot of stress on that spot. I've had some seriously hard hits to the front suspension, so that force had to be absorbed somewhere (besides my back)

Thanks for all the feedback................

[Vanimal]

This is why I believe one of the reasons Quigley chose to do link arms. The second being simplicity. The third, trying to follow existing design and frame strength design. Ford vans have krinckle front horns for accident absorption, which means the frame may also be thinner in this front area. With leaf type conversions a large % of the load carrying combined with now twisting of the frame without additional front stiffening is what can cause these cracks. I've done both types of conversions and seen the stress it can cause first hand. My 2 cents again, I'm in at 4 cents now.

[arctictraveller]

Originally Posted by Vanimal

This is why I believe one of the reasons Quigley chose to do link arms. My 2 cents again, I'm in at 4 cents now.

That’s likely and probably worth at least .25 cents, thanks.