Hi all. I just bought a 1986 3/4 ton GMC High Sierra 4X4 and there is a small split on the outside face of the right rear frame rail. I figured out a way to weld holes the other day and would like to try it with a MIG welder. Can you tell me what kind of steel the frame is made out of (I'm thinking carbon steel) and whether or not I can fix it with a MIG welder? Thanks!
Theoretically, yes you could weld it. Practically, not really a good idea. The weld will reduce the strength of the frame, possibly by as much as 80%. Better to through bolt a metal brace, IMO, if you can, but if a frame is bad, it generally can't be economically correctly repaired.
1. any heat treated alloy is annealed thereafter, or it will crack; too hard; taking welder to it overhardens alloys, as they harden at room temperature.
2. any long objects will warp, if a local high heat is applied. that;s why they normally do this in jigs, under longitudinal stretch, to prevent warp.
i second Big on this. drill and brace. basically, shackle it. or even better off, rid of it. donate and write off on taxes. one way or the other you mend it, it will only get weaker.
I really must disagree with the rest of the posters, in general. There is generally no problem with welding a frame but the twist is, it does require somebody that knows what they are doing and understands how to repair it and why you repair it as you do. As well, you need to figure out why it cracked and consider that when considering a repair. If the metal is degraded (it is 25 years old after all), the frame may have rusted enough to make it unrepairable.
The comparison to a semi tractors frame is not a proper comparison. A semi uses different metal and it is much different in the loads placed on it. It is high tensile strength metal that is quite prone to damage by improper heating. You truck is very different and not subject to the same stresses.
Now, you do not just go willy nilly welding a crack and think it is repaired though. Depending where the crack is and the condition of the abutting metal, you generally need to apply a fish plate. This is something that unless you are the pro at the welding shop that repairs frames, you take it to the pro at the welding shop that repairs frames. It is a very serious matter and shouldn't be taken on by a novice.
So, if you want to keep the truck, find a weld shop that does frame repairs and let them inspect the thing to determine if it really is repairable.
Ok. I'll post a picture later on when I get home. It's on the right rear frame rail just in front of the rear bumper brace for that side. Can frames be welded without a fish plate? I'd like the repair job to look like it was never cracked in the first place. Nice and smooth. Thanks!
A flitch beam (or flitched beam) is a compound beam used in the construction of houses, decks, and other primarily wood-frame structures. Typically, the flitch beam is made up of a steel plate sandwiched between two wood beams, the three layers being held together with bolts. In that common form it is sometimes referenced as a steel flitch beam. Further alternating layers of wood and steel can be used to produce an even stronger beam. The metal plate(s) within the beam are known as flitch plates.
Ultimately, it doesn't matter what you call it as long as people understand what you mean. From my experience, a fish plate is simply plate which is used as a reinforcing member in a limited area such as a joint or a crack repair. A flitch plate or beam would be a complete construction of a multi-layered beam. The plate I suppose would be the steel plate in the center of the two wood members.
I can make it look like it was never cracked but the problem is; it will not be an adequate repair. If your thought is to do this in an attempt to hide the problem and sell the vehicle: don't do it. It could cause you to not only be liable for the deception when it came time to look at rescinding the contract, it could also put you in a position of liability should that crack and subsequent repair fail and be the cause of an accident. God forbid a person would be injured. If that were to happen, there could be criminal as well as civil penalties involved.
I can't imagine an 86 vehicle looking all that sweet anyway so why a invisible repair is so important makes the intent a bit suspicious.
I'm not trying to hide anything. I just bought the truck actually. I'm using it as a work truck and I'm passionate about 73-87 Chevy and GMC trucks. I'm planning on restoring it, but I'm trying to figure out a way to restore it in a quality way. I have to repair the frame for this to happen.
Ayuh,... Short of replacing the frame rail, it might work Ok...
Btw,... Cut the fishplate in a diamond pattern, 'n do NOT weld the ends completely....
It'll keep the rails from crackin' at the ends of the fishplate...
When you say the ends of the fish plate, you mean the points? Like the top, left, bottom and right sides of the diamond shape?
Jesse
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