Welding firewall holes before finishing rewiring, Advice?

Well the rewiring is going well and i have decided to to some firewall cleanup while it is clear of wires. I have a series of holes, not sure from what that are filled with silicon. Two of them are near the heater holes, almost as if there was another heater.

Any advice on welding these up? I plan to strip the interior of the firewall and clean that up first. Denis

 

How big are the holes?

For small ones I'd weld them shut with gas and use baling wire as filler. It is very soft, grinds easy and can be planished quickly. Fill the hole, grind the excess off then planish with a hammer and dolly until flat and it doesn't oil can.

For anything more than about 3/8 inch, I'd make a plug out of some scrap automotive sheet metal, hold it in place with a magnet and butt weld it in. You might consider using EZ Grind wire in your MIG and grinding/planishing as you go.

There's a good tutorial on garagejournal.com forums in the "Fabrication and Techniques". Search "MP&C" and you'll find Robert's excellent tutorial on welding automotive sheet metal with a MIG

Whatever you do, make sure all that silicone sealer is 100% gone before welding anything. Keep a fire extinguisher handy.

 

Just to make sure I'm clear, you want black annealed iron wire for filler for the small holes - not galvanized wire. (You can buy low carbon steel welding rod if you want, but for non-structural applications, the black baling wire works fine.)

 

Thanks, I have about 5 holes slightly bigger than a quarter, I have some sheet metal plugs. I also have copper magnets to help hold pieces in place until tacted. I will be using mig and co2. I have compressed air in my garage to keep cool and a fire extinguisher! I will look into ez grind wire. I have a nephew who is a body guy and he will help get me started. Thanks for the tips.

 

They had me weld in washers that just fit the hole and then weld the small hole up when done.

 

You could also use a step bit to enlarge the hole and buy some blanks to fit the hole. I searched '18ga steel disc' on ebay and found these -

1" Dia. x .035" 18ga Steel Sheet Circle Disc Plate (Lot of 10) | eBay

A washer would work too. The key is a tight fitup of the plug to the hole

 

Thanks all here is the plan.

1. clean firewall
2. welding blanket to protect
3. using blanks, copper magnet prefit holes
4. practice with mig prior to real work
5. tact weld and cool,
6. grind flush
7. preserve

 

or you could go this route ..material of your choice

 

sorry photo didn't go thru

 

44 holes later

 

Very nice! Here is the passenger side view. The large hole is heater motor, the two to the right and below are the hoses for coolant. No idea what the rest are for? The oval one looks factory?

I am a novice welder and need to go slow and thoughtful. Denis

 

We don't weld firewall holes at all anymore. Grind around hole on inside, cut patch bigger than hole, butter patch with 3M Panel Bond and push into place. While one hole is welded you can do 20 with panel bond, be as strong (or stronger) and get zero warping and splatter. Chevy has panel bonded their door hinges on since the 90's and I don't see doors laying along the road. Picture of a 49 done 20 years ago.

 

Coilover is that an epoxy type material?

 

That sounds great. So you put a patch (temporary?) on the inside and then spread the material on the other side? DO you then sand it smooth? Denis

 

Ok I have watched numerous youtube videos and am still foggy on how to use the 3m patch, I really like the idea. I think the process is as follows, please confirm

1. clean
2. patch is slightly larger than hole.
3. Apply adhesive to patch and mount patch on the cab side of the hole


So no more hole but there is a recess on the engine side? what do you use to fill it ?

 

If you are a glutton for work you can rough up the engine side of the firewall and use all panel bond but it is HARD sanding. We use 36 grit on the whole patch so when it's in place you can just use regular filler. The firewall is just 0.062 thick so the filler is kept very thin. It is a two part epoxy type bonding agent. Also great to patch unwanted holes in dash or butchered radio holes.

 

Thanks Evan

 

I have many small, but important jobs awaiting my GMC. Filling the radio knockout is just one. Filling firewall holes as Evan has stated is another. Fastening a new tailgate stake pocket to the bedside is another. Can't wait. The stuff is pretty pricey, but as good (or better than) welding? Priceless!