Need to know what gauge metal to use to repair a few small sections of subframe. As I put my new pans in, I'm fixing things I did wrong many years ago. I had gotten into the subframe in a few areas on the flats with the arc welder and "fixed" them.....which of course meant more arc welding. My skills back then were rudimentary to say the least. I found some lumps and bumps underneath. I'd rather not get into the ugliness of the repairs. Suffice it so say I plan to fix it right.

I could grind and weld but some slag may remain and I'd rather have my frame solid metal. Maybe its just me but I prefer it that way.
Safest best is to cut those areas out and replace them.

Question is....what gauge metal should I use? Looks like 14 gauge maybe? Also does it need to be hardened or heat treaded or something? Or is it just mild steel? I need to fix this right before proceeding.

Areas I want to cut and replace are circled.

Thanks
Dave


(PS...pretty photo huh? The only way to get my "homemade pans" out was to cut around my original welds. I'm going to hit the boneyard and look for an entire tunnel. If I can't find one....it's fabrication time)

Aftermarket frame rail patches are made of 13 guage, but for repair and/or replacing the areas of the tranny cross member in your pics, I wouldn't be afraid of going one step thicker and using 12 guage.

I have bought the ART frame caps and they are 13 gauge. I have seen in several sources that factory was 14 gauge.

Speaking as a former welder, (24+ years), it never hurts to go a little heavier with frame repairs. But you can get into over kill where the fix won't flex where the original did and cause new stress cracks. Heat treating makes no difference unles you're heat treating again after welding and you really can't make mild steel much harder. It doesn't have enough carbon content. Thats what makes tool steel hardenable. MIG or Stick?? -- No more that 2 ga heavier with mild steel and good solid welds and you should be good to go.

Thanks for all the suggestions.

Scott...do u think I might end up with stress cracking at the welds even If I use the same thickness metal?

If so....is there any way to avoid them? It's in a bad spot right in the middle where left right body twist might occur.

I'm going to bevel both sides of the frame and repair piece for full penetration. I have both a MIG (argon/co2) and AC arc welder. I'm much better at arc welding now even though I don't do it much...but I'd rather use the MIG on a frame to reduce any chance of slag in it.

After the repair on the flats...Do you think I should weld a flat piece on the inside as a gusset to prevent any flex in those areas so the flats won't be able to flex there and crack?? OR...should I maybe put a piece across the tops?

Would extra support in those areas be good or perhaps lead to additional stress that might crack the welds...or the frame in other areas?

NEW photo shows possible supports. 1= small wedge on the inside of frame. 2= same wedge but with a 90 that extends to the base of the frame. 3= piece across the entire top that extends over the welded repairs. I'd apply this to front and back. Will any of this help? Or should I just cut and weld in new metal and forget it?

Dave,
I think you'd be ok to just put a strip across your weld like a band aid then weld all the way around it. Make it about twice the lenghth as the crack. I'm surprised that frame material is that light though. 14 gauge is just over 1/16" thick (.07" -.08") depending on the mill's specs. I would have expected it to be more like 12 gauge or .10" - .11" But if it is that light, you shouldn't need to bevel the frame pieces. Just don't grind the welds down flat before you weld on the "band aid" unless your using wire that is less than .030". If it is heavier than 14 ga or your using smaller than .030" wire then do bevel it. If you are using a 110 volt MIG machine, I personally wouldn't use it on structural members like a car frame. They're better suited to body metal and exhaust pipes. However, if you have a good 220 volt that puts out 130 or better amps then it should be plenty hot as long as you don't get in a hurry.

hey dave-what scott said.practice 10/12 gauge with your welder.also grind off your old weld.[do it slow,watch the color-cherry red o.k.-blue bad]fabricate your replacement parts so they overlap your old welds.a good vice,anvil,ballpen hammer channel locks get you started.your patches will be easier to file thinner or drill weld holes while they are flat before you shape or bend them.use cardboard to mock them up.you will be shocked [not by your welder hopefully] of what you can create to fit over your old welds and burn into virgin metal.NOTE:before welding -clean surface[denatured alcohol or windex]treat metal with anti-rust and let cure awhile

Thanks guys. Great tips! I'll have to look at my MIG and the wire size. It is a 110v but if I recall...it is 130 amps. I could be wrong but I think I'm using .023 wire. I find the best results on this welder are to set the speed to 0 ....so I'm always working slow whether it's sheet metal or thicker. Maybe when I cut and put the new metal in I'll MIG it and then use the arc welder on my band aids for best penetration. I'll decide when I get there.

Let you know how I make out.
Thanks again!

I guess maybe I have miss-interpreted what you guys are calling "sub-frame" Your talking about the supports that are welded to the underside of the floor pans and such right? I was doing most of my posting from my laptop and wasn't seeing a very good picture of Dave's repair area. I can see why that might be lighter material than what I was thinking. I was thinking of sub frame as in the sections that support the rear end and front suspension. This doesn't change any of my welding advice though, and I agree with all that plumkraz1 said too