Best way to repair stress crack in frame?

i would grind them out and weld them up. then weld plates over them for extra support. im no expert but thats how id do it.

tigerShark said:

i would grind them out and weld them up. then weld plates over them for extra support. im no expert but thats how id do it.

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The book says to drill a hole at the end of the crack, weld up the crack and then add supporting material as necessary.

8Mud said:

The book says to drill a hole at the end of the crack, weld up the crack and then add supporting material as necessary.

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guess im not too far off then.

"Stop-drill" the crack - 1/16" at the each very end usually serves for sheet (larger holes for thicker sections.)

Grind a slight "gouge" along the crack. This not only makes it easier to get good penetration on the weld, but also gives you good base metal for the weld to dig into.

Weld, including the "stop-drill" holes.

Grind flat.

Typically, you'll want to make the "stop-drill" holes about the same size as the thickness of the material, but usually 1/16" is a minimum (for sheet) and you can go up to about 3/16" - maybe 1/4" - for heavier sections (castings and the like.)

One more little hint. Lightly sand the crack and make sure you stop drill at the end of the crack. If you don't it's gonna start growing on ya.

Personally, in my experiences with repairing frames/unitbody, the stop-drill and weld is a standard great fix. but i also would brace the frame with diamond shaped plates, the shape of the plate really does matter, center punched to plug weld for strength. i would probaly make the plate about 2 inchs past the crack on both sides about 3/4 in away from the top and bottom of the frame.

Make sure to keep heat to a minimum. the rails are made from hsla steel. Mig is your best bet to control heat.

bfred said:

Make sure to keep heat to a minimum. the rails are made from hsla steel. Mig is your best bet to control heat.

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You want good heat control use a window cleaner pump sprayer filled with water, wet it down, weld it up. The water doesn't affect the weld a bit, but does control the heat leech and possible annealing of surrounding material.

thanks for all the great tips! I plan on using a heavier duty hitch with four mounting points after the repair, could a guy drill some holes in the frame and plug weld angle iron on the inside of the frame box to strengthen it up??

just in the area of the hitch maybe two 16 inch chunks? or not so good idea?

I've used wet rags close to the area that's being welded, or heat control compound (putty-like substance available at welding supply). Would spraying water (especially after welding) make it cool too fast, making the weld brittle?

bfred said:

I've used wet rags close to the area that's being welded, or heat control compound (putty-like substance available at welding supply). Would spraying water (especially after welding) make it cool too fast, making the weld brittle?

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Yes, it would. If you want to retain ductility and minimise hardness/brittleness in the HAZ, go with a post-weld slow cooling by using a torch to slowly cool it off.

Water is going to be too much... Air-cooling will give you more ductility than water cooling, since it's slower.

5-90 said:

Yes, it would. If you want to retain ductility and minimise hardness/brittleness in the HAZ, go with a post-weld slow cooling by using a torch to slowly cool it off.

Water is going to be too much... Air-cooling will give you more ductility than water cooling, since it's slower.

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I don't use water to cool, which hardens, I use it before, so the steam/evaporation leeches some of the heat away from the surrounding metal. So you lessen the possibility of leaving a rather large ring of very unequal tempers. Wetting it down before welding and letting the water steam off helps eliminate warping, it's quicker and cheaper than heat gel or newspaper soaked in water and corn starch. Wetting before welding is all thats often necessary for many welds to control warping and stepped temper (hard to soft) in the surrounding material..
Slow cooling with a torch is the way to go for many welds, MIG welds are hard, some carbon is added during the welding from the shield gas breaking down (depends on the shield gas and wire type) and the material itself.
The frame seems to be true steel or nearly so, harder than standard sheet metal. The problems start an inch or so away from the weld when the surrounding material is heated to 600 degrees or so and left to cool slowly, it can get really soft.
Where the harder weld meets the softer (annealed) sheet steel is often where the next crack starts.

Grind a slight "gouge" along the crack.
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It also make it easer to keep the crack in the center of your bead.

I had this same problem with stress cracks. I've got two cherokees, one that I use as a daily driver and to tow a boat, the other that I just use for wheeling.

I noticed a lot of squeaking while towing and when I investigated there was some pretty serious damage that had been done to the unibody on the driver's side. I pulled the hitches off of both of my jeeps and even though they were rated for exactly the same amount 3500 / 5000 weigh carrying vs. weight distributing, the design was radically different.

The one I'd been using to tow my boat mounted to the body with just a 1.5" x 6" flange on each side, while my other hitch had a 2" by 18" flange on each side, plus a mounting bracket directly in the center. The whole thing was just massively stronger and designed to spread the load over much more of the unibody. If you're having this problem I would strongly recommend looking into a different hitch. I don't know what brand the beefy one I have is, I got it from a parts jeep that I had - pretty sure it was made in the 80s though. The wimpy one that I had was a North Star, which I think is a Northern Tool brand.

Towing a trailer is too serious of business to trust to a poorly engineered hitch.