How to fix a cracked frame?

[Brian L]

I have found some cracks in the frame on my 88, 1500. The small diagonal crossmember next to the spare tire is cracked almost all the way through, and then the curvy crossmember that holds the tire is cracked about two inches on the bottom where the two meet.
Also there is a crack at least 6 inches long on the bottom of the frame under the driver side door, and another one maybe 4 inches long on the side above it. It is right before the frame starts to curve up towards the engine. There is a big dent on the bottom of the frame that almost looks like this corner of the truck was driven off a brick wall or something. But the guy I bought this truck from was a drunk so I wouldn't be surprised.
I asked my welding instuctor about maybe welding these cracks up. He said not to weld a frame because it would change the temper of the metal, and possibly sag it making it even weaker than it was before. He also said with the amount of scale and rust on the frame that you would have to grind a lot of it down to make it clean enough to get a weld to stick on also making it thinner and weaker than before. This frame is very rusty, and there is lots of scale peeling off. Instead of welding he recommended drilling some holes in the frame and bolting in a piece of angle iron over the cracks. I think what he said makes a lot of sense, but I just want a second opinion. What do you guys think about this?

[bagged69c10]

I think if the frame is rusted then grinding off the rust isnt going to hurt anything. Rust typically isnt very strong and I doubt the strength of your frame will weaken by grinding it off. I would weld it and put some 1/4" plate over the weld and it up too. Sounds like the guy was a stunt driver or something.

[cdowns]

from the sounds of the condition of the frame i'd drill holes at the ends of the cracks use a cutoff wheel to V the crack and use a stick welder for max penetration also adding a reinforcing fish plate or even boxing sections of it wouldn't hurt

[67Fleet]

Sounds like a candidate for a donor frame. I would also agree with boxing in the sections where it's cracked. That will give it some good reinforcement. I'd also carefully inspect the rest of the frame as well. Are you the original owner? Could be a vehicle that has been wrecked by a previous owner and a shoddy repair done without proper inspection.

[PBFAB.COM]

Originally Posted by 67Fleet

Sounds like a candidate for a donor frame.

I would agree with that! Sounds like the frame is in pretty rough condition. Have you thought about looking for a replacement frame? Make a few calls to some wrecking yards and see what kinda prices you find. You may be time and money ahead scrapping the frame you have and starting with one in better condition.

[TravisH]

Toss the frame. Theres probably a lot of hairline cracks that you can't see underneath rust and grime. With that much damage I would be surprised if the frame wasn't tweaked as well.

As for your welding instructor, hes mostly correct. When you weld a piece of metal the rapid heating and cooling changes the properties of it (eg. brittle vs ductile). To get different properties involves preheating, postheating and submersion cooling, all of which is out of the scope of the course you're taking right now. You'll probably touch on it but won't do any work with it. Now its possible to weld that frame and have it returned to the original state, but you would need to find out the exact process and temperatures you are dealing with. Its not something I'd recommend to a journeyman welder.
That being said you might wonder why a lot of people (including myself) are welding on these frames. You've got basically two types of frame, light passenger and heavy truck. Light passenger vehicles such as our trucks don't see a whole lot of stress in comparison to heavy trucks and therefore any change of temper is pretty much negligable on a solid frame, if the weld is allowed to cool naturally or with post heat. Different story on a heavy truck and thats where the properties from heat treating really come into play, so much so that on semi-tractor you are not allowed to have a weld within the axles. The frames go through enough repeated flex under heavy loads that it will crack period. DOTs see that and your off the road, big fine, and I wouldn't be surprised with criminal charges. However other heavy trucks that don't carry trailers can be welded on.

Sorry if I got a little off topic on your question but hopefully now you understand what your teacher was talking about. The reinforcement methods talked about above all work but in your case scrap the frame. It shouldn't be much more than a couple hundred bucks for a roller and I guarantee theres more wrong with your frame than you think

[72CSTC5]

Replace the frame

[cowboy33713]

Howdy:
I'm not an expert, but have to think this can be fixed. Have seen on this site a very detailed procedure, with photos of the work being performed (so this was not just a "what if" exercise) wherein a lwb truck had the bed removed, the frame cut, a section removed, then the shortened back end welded back to the front, to make a SWB truck. Race car and Rod guys weld on their frames all the time. Just my observation.
cowboy33713

[Brian L]

Yeah he was saying something about how he used to work on tractor trailers with heat treated frames. I don't think this frame is bad enough to replace at the moment though. Believe me, I don't think there is much of a stress issue with the way it is cracked. All the cracks run length wise along the frame. If I found a crack that ran vertically though then that would be a big problem because it would be peeling in two. As far as I know, no such thing exists because I looked it over pretty damn good. As for that crossmember I spoke of that was cracked almost all the way though, that thing is more of a brace for the spare tire than any thing else. It is too small to be considered an actual crossmember. I could easily realace that anyhow. And I know that the junkyards around here would want more than a couple hundred dollars for another frame, considering I couldn't even find a rebuildable 350 small block for less than $450. The cracks by the spare tire I just found the other day, but the 2 big ones under the door I have known about since I bought the truck, and I don't think they have gotten any bigger with over 10,000 miles of driving. I think they are repairable so I am just going to bolt some angle iron in over them. I should probably drill a hole at the end of the cracks to prevent them from getting bigger right?

[67Fleet]

yes, that will prevent the crack from spreading further.